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National Astronomy and Ionosphere Center Arecibo Observatory

N AT I O N A L A ST

Y AND IO NO OM ON S R

AR EC RY IB O TO O B S E R VA

Space and Atmospheric Sciences u r i n g J u n e 11 - 1 5 N A I C s t a f f Qihou Zhou, Craig Tepley, Shikha Raizada, and Jonathan Friedman, aided by REU summer students Ingrid Pla (UPR-MayagÝez) and Daniel Kao (Penn State) carried out an observing run that focused on simultaneous lidar and radar observations of E-region layers. This marks what may be the first successful simultaneous observations of a specific ion, Ca+ in this case, and electron density (Ne). Temperature using the K lidar and winds, from the ISR, were also measured in the mesopause region. Dave Hysell (Cornell) was operating a VHF radar on St. Croix during this period in preparation for a study of quasi-periodic

ENTER EC ER PH

NEWSLETTER
(QP) echoes carried out later in the month. Also, Michael Mendillo, Steve Smith, and Joei Wroten (all Boston University) have installed an all-sky camera at Arecibo that recorded images during this period of lower thermospheric emissions from OH (rotational lines from 695 to 950 nm), Na D2 (589.3 nm), O(1S) (557.7 nm), and, from the F-region, O(1D) (630.0 nm). On June 14-15 they observed the unusual phenomenon of a broad nighttime E-region electron layer. This layer persisted from dusk to after 0300 local time, and had a particularly large extent from 2300 to 0230. A Ca+ layer was observed that corresponded closely in extent and structure to the E layer. These overlapped the normal K layer, which, in turn, expe-

November 2002, Number 35
Photo: Jonathan Friedman and John Toohey, 2002

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rienced a very strong enhancement as the E and Ca+ layers subsided. Figure 1 shows cuts from these layers, corresponding to one hour averages between 0000 and 0100 local time. Also shown is the mean temperature profile from 81 to 108 km recorded by the K lidar at the same time. An initial report on this observation has already been submitted for publication in Geophysical Research Letters (Tepley et al., in press). The June 14-15 data set, because of the unusual E-region as well as the broad suite of instruments observing it, is of special interest. Examples of the VHF radar and imager results

INDEX
Space and Atmospheric Sciences..... 1 Paul Goldsmith Steps Down ............ 3 A New User's Experience ................. 4 Radio Astronomy Highlights ........... 6 Solar System Studies ...................... 19 Receivers and Related .................... 21 ALFA Extragalactic HI Meeting ... 22 From the Electronics Department. 22 Education and Outreach ................ 24 New North VSQ done ..................... 25 Computer Department News ......... 26 Comings and Goings ...................... 26 "Children of the Stars" Review ..... 27 Job Opening at AO ......................... 28 Recent Colloquia............................. 30 "Single Dish Techniques" Proceedings Available ...................................... 30

Mean MLT Region electron layer, Ca+ layer, K layer, and temperature between 0000 and 0100 for 15 June 2002
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Mean E-Layer

Mean Ca+ layer

Mean K Layer

Temperature Profile

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Figure 1: (a) Electron, (b) calcium ion, (c) potassium and (d) temperature profiles in the mesosphere-lower thermosphere region recorded between 0000 and 0100 local time on the night of June 14-15, 2002. (Courtesy: Jonathan Friedman)

The NAIC is operated by Cornell University under a Cooperative Agreement with the National Science Foundation.


320 300 Range (km) 280 260 240 220 200 0:00 0:30 1:00 1:30 2:00 Local Time 2002/06/14-15 30 2:30 3:00

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Figure 2: Range time intensity plot from June 14-15, 2002. Grayscales represent signal-to-noise ratios in dB. Range corresponds to distance from the radar, not vertical height. The E-region above the Arecibo telescope lies in a range of about 240 km from the radar as can be seen in Figure 4. (Courtesy: Dave Hysell)

Bishop (Clemson University), and Dave Hysell and Lynette Gelinas (Cornell University) in June and July of this year. The investigation focused on socalled quasiperiodic (QP) echoes which were first observed at the MU radar in Japan over a decade ago (Yamamoto et al., 1991, JGR 96 and 1992, JATP 54) and have since been observed at other locations in the Pacific, American, and European sectors. Detected principally by VHF coherent scatter radars, QP echoes signify the presence of field aligned plasma irregularities, colocated with sporadic E layers and thought to be generated by complex interac tions between the neutral atmosphere and ionization in the mesosphere and lower thermosphere (MLT) region. The investigation sought to answer three fundamental questions: First, what are the processes responsible for generating the QP structures? Several primary mechanisms have been proposed for initiating QP. Some of these rely on various unstable sporadic E layer configurations including tilted layers, multiple layers, and deeply modulated layers. Others stress the roles of the background neutral motion, gravity waves, or Kelvin-Helmholtz billows that develop within the neutral wind shear that generates the sporadic E layer. The small-scale structure that ultimately produces the coherent scatter observed at VHF is assumed to be the gradient drift instability in all three mechanisms, although the Q P initiation mechanis m will obviously influence how and where the instability condition is satisfied. Second, what is the range/altitude extent of the QP structures? The simple and commonly used assumption that the VHF backscatter is highly aspect sensitive and maximizes within a fraction of a degree of the direction perpendicular to the magnetic field, B, leads to a direct proportionality relationship between range and altitude. The measurements made with the MU radar and other coherent scatter radars, which have been interpreted using that simple relationship, suggest that the structures extend from

are shown in Figures 2 and 3. Figure 2 shows QP echoes, indicated by the elongated streaks in the plots, and continuous echoes in the diffuse background backscatter. Read more about the VHF radar in the "QP Echoes" section below. All-sky images of the O(1S) emission at 557.7 nm and Na emission at 589.3 nm are shown in Figure 3. These show a
O(1S) 557.7 nm 04:29:37 UT (a) North

northeast propagating wave just prior to the initiation of the strong sporadic E. QP Echoes Dave Hysell A n i n v e s t i g a t i o n o f p l a s m a i r r e g u l a r ities in midlatitude sporadic E layers was undertaken by Miguel Larsen and Rebecca
Na 589.3 nm 04:27:18 UT (b) North

Arecibo Obs

East

Arecibo Obs

East

Boston University All-sky Imaging System
Figure 3: These are images in the night time mesospheric (a) 557.7 nm and (b) 589.3 nm emissions at Arecibo Observatory obtained with the Boston University All-sky Imaging System on June 14-15, 2002. A wave event can been seen in the images propagating towards the North-east. They are time-difference images, i.e. two subsequent images subtracted from the other. They are also unwarped, i.e., the images have been mapped onto the earth's surface using star positions and assuming heights of 96 km (O(1S)) and 90 km (Na) for the emissions. A circular mask is placed on each to remove distracting trees and things like that. The 557.7 nm emission exhibited waves during most of the night but the Na emission showed waves after about 04:00 UT moving towards the north-east. These waves can also be seen in the 557.7 nm emission. (Courtesy: Steve Smith)

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Paul Goldsmith Steps Down

A

fter ten years in the position, Paul Goldsmith has decided to step down as NAIC Director to dedicate himself full time to the Cornell University Astronomy Department, where he is the James A. Weeks Professor of Physical Sciences. Paul has led the NAIC through trying times as it has reinvented itself as an observatory and national center. His contributions to the long list of upgrades and additions that Arecibo Observatory has undergone during this period have been enormous. As well as overseeing the Gregorian upgrade from beginning to end, Paul presided over NAIC during the creation of the àngel Ramos Arecibo Observatory Visitor and Education Facility and its recent add-on Learning Center, the restructuring of the Atmospheric Sciences Department into Space and Atmospheric Sciences with its own Assistant Director, the new lidar laboratory, and most recently the construction of new visiting scientist quarters. However, it is the Gregorian project that has defined Paul's years at NAIC, and to which he has made his greatest contributions. He has personally led the receiver development program for highest frequency available to users of the instrument move up from NAIC into the 21st century with a state-of-the-art research capability. health, for which we are most grateful. He will be missed by all, but at Arecibo as a regular user of the telescope.

the 305-m telescope over these ten years, seeing the 2.4 to 10 GHz. It is the Gregorian upgrade that takes Paul leaves behind an observatory that is in excellent we console ourselves that we will be seeing him often

Cornell University has set up a search committee under the leadership of Professor Joe Burns to hire the new director for NAIC. The position has been advertised in various professional journals and publications, and nominations and suggestions from the community would be most welcome. These can be sent to Prof. Joseph A. Burns, Search Committee Chair, Office of the Vice Provost for Research, 314 Day Hall, Cornell University, Ithaca, NY 14853. E-mail messages can also be sent to naicsearch@cornell.edu. 90 or 95 km altitude to altitudes of 120 to 140 km, and sometimes even 160 km in the lower E region. Sounding rocket measurements are obviously much more limited in both their spatial and temporal
19.0 Latitude (deg N)

coverage than the coherent scatter radar measurements, but the few observations that are available do not show evidence of significant electron density or electric field perturbations above heights of 115­120 km. Third what is the relationship between the motions of the ionization structures in the sporadic E layer and the range rates and Doppler shifts observed by the coherent scatter radars? The observed Doppler

18.5

18.0

shifts generally differ in magnitude from the range rates, i.e., the range vs. time slopes associated with the QP structures in the radar RTI's, and they are sometimes in opposite directions. Since coherent scatter is produced by wave structure at half the radar wavelength, the motions inferred from the coherent scatter radar observations are the phase speeds of that structure. Interpreting those results without knowing the broader context is difficult. A series of observations of sporadic E layers and QP echoes was therefore carried out above Puerto Rico using the Arecibo incoherent scatter radar and a coherent s catter radar deployed at the U . S . Vi rg i n I s l a n d s N a t i o n a l G u a r d Armory on St. Croix in order to address the three questions listed above. The

17.5 -67.5

-67.0

-66.5 -66.0 -65.5 Longitude (deg E)

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Figure 4. Map of Puerto Rico and St. Croix (lower right). The arcs denote distance from the radar on St. Croix to scatterers at 100 km altitude. Other curves represent the locus of perpendicularity from St. Croix at different E region altitudes. (Courtesy: Dave Hysell)

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A New User's Experience at Arecibo During an Investigation of Sporadic E and Quasi-Periodic Echoes
Rebecca Bishop, Research Associate, Clemson University Sporadic E (Es) are plasma layers that develop through the interaction with the neutral winds between 90 and 120 km. These layers are often observed by ionosondes and incoherent scatter radars around the world. In the past decade another phenomenon that occurs in conjunction with Es, Quasi-Periodic (QP) echoes, have been observed by VHF or HF radars. QP echoes were first observed in the early 1990's by the MU radar in Japan but since then have been observed at many locations around the world. Although observations of QP and their characteristics have increased in the last decade, many questions still remain regarding the relationship between QP echoes and Es layers. The generation of QP, the horizontal and vertical extent of QP structures, and the relationship between ion motion and structures of Es and observed QP, was the principal focus of an investigation this summer by Miguel Larsen (Clemson) and Dave Hysell (Cornell). During the experiment (June 19 to July 4), my role was to determine the radar mode and monitor the Arecibo observations each night. The nighttime E region electron density was observed at a resolution of 300 m using Arecibo's 430 MHz transmitter . Initially a single beam was used but during the second half of the experiment period the new dual beam capability was utilized. By continually scanning the azimuth with two beams, the horizontal extent and structure of the sporadic E layers were measured. Simultaneous observations were also made by a coherent scatter radar located on the island of St. Croix. The 30-MHz portable coherent radar, built and operated by Dr. Hysell, was oriented such that the beam was perpendicular to the magnetic field above Arecibo allowing backscatter observations of the same volume. Although the observation period occurred during the summer months when Es occurrence peaks, only a few nights of strong Es were observed. Coincident quasi-periodic echoes observed by the coherent radar lasted from a few minutes to over 30 minutes. Currently, analysis is underway to determine the relationship between the observed Es and QP structures. As a new user, working with the Arecibo radar was a great experience. The 430-MHz radar is a unique instrument with unrivaled capabilities for studies of the ionosphere. Walking into the control room the first time and seeing the complicated patch panel setup used for the experiment was daunting at first, but the staff took the time to explain it all until I was confident that I could set up the experiment myself. Both the science and technical staff were friendly and professional, taking time to answer questions and providing support even after the experiment had finished. Overall, I have gained a greater appreciation for the science potential of the facility and look forward to working with the observatory and staff in the future. The staff were very helpful and friendly which made the overall experiment a success. Special thanks go to Qihou Zhou, NÈstor Aponte, Sixto GonzÀlez, and Mike Sulzer, as well as the radar operators, for all of their assistance related to this investigation. observations utilized the newly devel oped dual-beam capability together with azimuth scanning to obtain information about the spatial and temporal variations of the E and F region ionization structures along with their motion. By locating the coherent scatter radar on St. Croix, common volume measurements in the E region above Arecibo were possible. (Figure 4 illustrates the geometry of the experiments.) Furthermore, the coherent scatter radar was configured for in-beam radar imaging, a technique that permits the unambiguous determination of the origin of the coherent scatter in three spatial dimensions. The experiments directly addressed the questions related to the generating mechanism, the altitude extent of the structures, and the relationship between the velocities inferred from coherent scatter measurements and the motions of the ionization. by the radar in range-time-intensity (RTI) format. As mentioned previously, examples of QP echoes (the elongated streaks) and continuous echoes (the diffuse background backscatter) are present in the plot. In this case, echoes were

Figure 5 is a photograph of the imaging coherent scatter radar deployed on St. Croix. The portable 30 MHz radar incorporates solid-state transmitters and operates with a modest peak power level of 8 kW. Sensitivity is recovered with the use of a long coded pulses, a high pulse repetition rate, and coherent integration. Coherent scatter from the plasma irregularities in question is also very strong at 30 MHz, and signal-to-noise ratios of the order of 30 dB were observed. Figure 2 (on page 2) shows a representation Figure 5. Photograph of of coherent scatter received Croix. (Courtesy: Dave

the radar site at the National Guard Base on St. Hysell)

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received without interruption for a period of almost 4 hours. The 30 MHz radar utilized five antenna arrays for interferometry and radar imaging. True images of the backscatter "brightness" distribution (the distribution of backscatter intensity versus bearing) within the radar illuminated volume can be formed from interferometry data taken with multiple baselines. It is well known that interferometry with a single baseline yields two moments of the brightness distribution. More baselines yield more moments, and a sufficient number of moments define an image in one or two dimensions. Radar range g atin g ad d s an o th er s p atial d imen s io n . An important feature of in-beam radar imaging that distinguishes it from beamswinging approaches is that the angular resolution of the technique is limited by the length of the longest interferometry baselines rather than the size of the main antenna array. It is therefore possible in practice to form very high resolution images with interferometry even using small radar systems like the 30 MHz radar which had interferometry baselines as long as 200 m. In-beam images formed from different Doppler spectral components can be combined into composite images, conveying information about the spectral characteristics of different regions of the illuminated volume. Animated sequences of images reveal how the scatterers evolve over time as they travel through the illuminated volume. Using a combination of coherent scatter radar imaging and incoherent scatter dual-beam azimuth scanning, it will be possible to identify the plasma structures in the ionospheric volume over Arecibo responsible for the QP echoes for the first time. Incoherent scatter will also make it possible to monitor the background plasma density, neutral wind, and electric field in which these structures are embedded, allowing us to quantify the instability mechanisms at work. Approximately 1 TB of data were taken between the two radars, which operated together between mid-June and early July, 2002, and the research therefore has IT overtones in

addition to implications for space sci ence. Data processing is computationally intensive, but early results are anticipated this fall Micrometeor observations Diego Janches Since January 2002 monthly radar observations of micrometeors have been perfo rmed by D iego J anches (N A I C) an d John Mathews (Penn State) in order to measure the seasonal variation of meteoric mass input in the upper atmosphere. These observations cover a period of approximately 14 hours (18:00 LT­08: 00 LT) and they are expected to continue until December of 2002. The 430 MHz dual-beam capabilities of the radar are used allowing us to study several regions of the sky simultaneously. Preliminary results show latitudinal dependency on the meteor velocity distribution, mass flux estimates and orbital studies. These observations are part of the NSF/CEDAR Postdoctoral fellowship awarded to Diego. Other observing programs Qihou Zhou From February 15­18, 2002 an experiment was carried out to observe neutral t e m p e r a t u r e , N e, a n d i o n c o m p o s i t i o n or ion-neutral collision frequency by running the K and Rayleigh lidars and the ISR 50 simultaneously. Another Vpn 40 objective of this study Vpn is to measure the diurnal 30 tide. The radar gives the 20 daytime temperature 10 measurement while the 0 lidars give the nighttime measurements. By com-10 bining the radar and lidar -20 results, we have nearly 24 -30 hr coverage of the meso-40 sphere.
Vpn (m/s)

15-17 period there was a World Day to study the penetration of storm effects into the lower thermosphere. A storm with Kp=6 occurred on the April 17 as described below. April Magnetic Storm Mike Nicolls On April 17-18, 2002, an intense electric field penetration event was captured by several incoherent scatter radars, including Jicamarca and Arecibo. Jicamarca is set up so that it probes nearly directly perpendicular to the magnetic field, which makes it the world's most sensitive electric field sensor, able to easily detect zonal fluctuations of 25 µV/m. What is particularly interesting about this event is that the Interplanetary Electric Field (IEF) correlates very well with the zonal electric field measured at Jicamarca, and the IEF is also apparent in data from the Millstone Hill, Arecibo, and Sondrestrom ISRs. This correlation is often difficult to observe because of the higher level of geophysical noise that is present in the electric field measurements of the other ISRs. (Kelley et al., submitted to GRL, 2002) Figure 6 shows the velocity perpendicular to the magnetic field line in the n o r t h w a r d d i r e c t i o n V pn m e a s u r e d a t Arecibo (solid line). The dashed line s h o w s a p r e d i c t i o n b a s e d o n t h e m e aArecibo, April 17 2002, 367km

calculated from JRO measured at AO

O was Day and

n March 26 there a o n e - d a y Wo r l d for the database, during the April

-50 0

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Figure 6: Vpn as measured at Arecibo (solid line) plotted against the predicted Vpn from Jicamarca (dashed line) for April 17, 2002. (Courtesy: Mike Nicolls)

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sured fluctuations in the zonal electric field at Jicamarca. These fluctuations are mapped along the field line to Arecibo using L3/2 (where L is the L-shell parameter from the McIlwain magnetic coordinate system). Fluctuations in Vpn for Arecibo are then calculated applying a model for the magnetic field. When added to a typical Arecibo quiet (non-perturbed) Vpn the dashed line results. The similarity between these data is striking c o n s i d e r i n g t h e d i ff e r i n g g e o p h y s i c a l conditions that these instruments see, with the Arecibo data appearing to be a "smooth" or "integrated" version of the predicted Jicamarca velocity. Similar correlation is seen in the Millstone Hill and Sondrestrom results. Researchers from Cornell University along with NÈstor Aponte from Arecibo and Jorge Chau from Jicamarca participated in the study of the electric field data, and also compared results with those of Larisa Goncharenko of Millstone Hill and Jeff Thayer of Sondrestrom. Many groups from institutions all o v er th e w o r ld ar e p ar ticip atin g in th e study of these events, and analysis still continues in many different areas, with frequent meetings to update the community. A special section at the Fall AGU Conference is also planned to further discuss the multifarious results that have come from the April 2002 storm events. Radio Astronomy Highlights Chris Salter HI in the Leo Triplet lberto Bolatto, Josh Simon, Tim Robishaw (Berkeley) & Fabian Wa l t e r ( N R A O ) h a v e c o m p l e t e d a n observational program to study HI in the Leo Triplet, one of the nearest strongly interacting groups of galaxies. They used the new GUI on-the-fly mapping routines to construct a sensitive, Nyquist-sampled map (Fig. 1) covering an area of > 3 sq. deg, and encompassing the entire Triplet (NGC3623, NGC3627, & NGC3628), plus the dramatic tidal features associated with NGC3628. Also visible are 4 small

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Figure 1: An integrated-intensity map of HI emission in the field of the Leo Triplet for the velocity range 200­1900 km s-1. The field was observed in a "boustrophedonic" pattern using the on-the-fly mode. Integration time on each point of the 1-arcmin grid was 2 sec. The raster was repeated 3 times, giving a final integration time of ~1 min per 3.3' beam; (a few rows at the top and bottom of the map have shorter integrations). The resulting sensitivity is ~25 mK in ~10 km s-1-wide channels. (Courtesy: Alberto Bolatto)

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TIDAL TAIL

NGC3628

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Figure 2: A map of the data in Fig. 1 convolved to a resolution of 4.8 arcmin to emphasize faint, extended structure. Clouds C & D correspond to peaks identified by Haynes et al., while Cloud A is probably the counterpart of UGC6387/IC2763. Cloud B appears to be a new bona-fide HI feature of the Triplet. (Courtesy: Alberto Bolatto)

clouds (labeled A-D in Fig. 2), two previously unknown, and a hint that the tidal tail containing Cloud C connects to the western side of NGC3627.

The best pre-existing HI observations of this system were made in 1976-77 by Haynes, Giovanelli & Roberts (ApJ, 229, 83), using Arecibo to observe the 3 main galaxies and the tidal tail to the east of

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NGC3628 on an irregular (~5 arcmin) grid following the emission. With the upgraded 305-m telescope, Alberto et al. were able to map a much larger area, sampled on a regular 1-arcmin grid, and with better sensitivity and velocity resolution. Cloud A is coincident in position and velocity with the galaxy pair UGC6387, probably a background source. The other new source (Cloud B) is at the systemic velocity of the Triplet, implying an HI mass of 107 M¤, and appears to have no optical counterpart. Their future plans include complementing the Arecibo data with VLA and BIMA observations, which will be used to model the Triplet interaction and the creation of tidal dwarf galaxies, and studying the formation of molecular clouds in this environment. Observations of Mini-HVCs Lyle Hoffman (Lafayette) & Ed Salpeter (Cornell) have mapped HI in the fields of 4 low column density sources at velocities appropriate to High Velocity Clouds (HVCs), identified with the Green Bank 140-ft by Lockman et al. These four fields exhibited emission only in Lockman et al.'s target fields, and not in the preceding and trailing reference beams. All were found to be quite clumpy on the scale of the Arecibo beam, much like the mini-HVCs found earlier by Lyle & Ed, which were superimposed on the outskirts of two HVCs. Each mini-HVC s ubtends 5­10 A recibo beams and has p e a k c o l u m n d e n s i t y ( N HI) b e l o w 2 â 1019 cm-2. One field, LMPU 236, is in the Galactic North with positive Vlsr. Lyle & Ed

found a single mini-HVC in this field, with NHI 2 â 1018 cm-2. LMPU 369, in the Galactic South with negative Vlsr, also has a single mini-HVC just off the edge of the 140-ft beam; this has NHI ~ 9 â 1018 cm-2. They also found a miniHVC in their reference beams for this source, 6 arcmin east in R.A. The other two fields proved more complex, with multiple mini-HVCs. The field LMPU 025 has three mini-HVCs, at Vhel = -163, -291, & -335 km s-1, with NHI = 2, 8 & 4 â 1018 cm-2, , respectively; it also has a fourth mini-HVC just outside the 140-ft beam at -389 km s-1, and yet another lies in their reference beams for this field. LMPU 387 has 3 mini-HVCs within the 140-ft beam, with Vhel = -275, -297 & -230 km s-1 and NHI = 5, 9 & 5 â 1018 cm-2, respectively, all superimposed on the northern extension of the Magellanic Stream, which they might be related to. However, the other LMPU fields are all angularly quite far from the Stream. Thus, Lyle & Ed have now indentified a grand total of 13 mini-HVCs. The implications of these low central column densities for ionization mechanisms (photo and collisional), for Ly- and other absorption lines in quasar and AGN spectra, and for the HVC distance controversy remain to be determined. An HI Search for Intergalactic Clouds with No Optical Counterparts Recently, an Arecibo HI line search was made by Chantal Balkowski, VÈronique C a y a t t e , Wi m v a n D r i e l ( P a r i s O b s , France), HÈctor HernÀndez, Karen O'Neil (NAIC), Pierre-Alain Duc (CEA, Saclay,

France), John Dickey (Minnesota), Jorge Iglesias-PÀramo (Lab. d'Astrophys. de Marseille, France), JosÈ VÌlchez (IAA, Spain) and Trinh Thuan (Virginia) of a dozen HI clouds in the Hercules Cluster (z ~11,000 km s-1) without optical counterparts on the Palomar Sky Survey. These clouds had been reported as tentative detections in the 1997 VLA HI survey of the cluster by John Dickey. Subsequent CCD photometry by this team has shown faint optical counterparts of 2 of the reported clouds, whose VLA HI detections are now reconfirmed at Arecibo. Although the Arecibo sensitivity should have permitted the detection of the other tentatively reported HI clouds, none were reconfirmed (Fig. 3), showing once again that intergalactic HI clouds without optical counterparts are very rare beasts indeed. HI in Low Luminosity, Nearby, HSelected Star-Forming Galaxies In work to be published in ApJ this Dec, a complete sample of 109 low luminosity (MB > -18.0), nearby (cz < 11,000 km s-1), H-selected star-forming galaxies from the KISS catalog have been observed at 21 cm by Janice Lee (Arizona), John Salzer (Wesleyan), Chris Impey (Arizona), Trinh Thuan (Virginia) & Caryl Gronwall (Johns Hopkins). The detection rate was 89% (97/109). Examining the KISS composite B- and V-band survey images, they find that 9% (10/109) have companions of comparable or greater optical brightness within the 3.5-arcmin Arecibo beam. They conclude that their non-detections and upper limits for confused sources do not bias the sample in

Figure 3: Arecibo HI spectra that do not reconfirm 3 of the tentative HI clouds without optical counterparts reported in a VLA HI Hercules-Cluster survey taken by John Dickey. The smoother profiles are those from the VLA. (Courtesy Wim van Driel)

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0

-1

-2

-3 Rosenberg & Schneider (2002) -4

dependent SFR is used to calculate timescales instead of a solar-metallicity SFR. Accounting for metallicity is important since the sample galaxies have low luminosities, and tend to be metal-poor. One interpretation of these statistics is that these galaxies will not deplete their gas supplies for another Hubble time if they continue to form stars at their current rate. These results also lift the requirement that BCDs have star formation histories dominated by short bursts of activity, and show that a more nearly continuous mode of star formation is possible. (v) By computing an HI mass function (HIMF) for this sample (see Fig. 4), it is shown that the low luminosity star-forming galaxies in KISS contain 1 0 - 1 5 % o f t h e o v e r a l l H I i n t h e U n iv e r s e . T h e y f i n d t h a t HI( K I S S M B > -18.0) = 7.0 â 106 M¤ Mpc-3, or HI = 4.5 â 10-5 with a ~20% statistical error. The HIMF of this sub-population does not exhibit a steeply rising slope at low masses, consistent with the result that gas richness (MHI/LB) does not increase at a significant level with decreasing galaxy luminosity. In the range 108 < MHI/M¤ < 109, they find that 25-50% of all galaxies are currently undergoing a strong episode of star formation. An HI-absorption VLBI Experiment on 3C138 Arecibo was one of 13 telescopes used by Joe Lazio (NRL), Miller Goss, Crystal Brogan (NRAO), Michael Faison ( N o r t h w e s t e r n ) , A s h l e y Z a u d e r e r, & Chris DePree (Agnes Scott) to observe 3C 138 in an HI-absorption VLBI experiment. Such experiments have been carried out numerous times toward 3C 138 (e.g., Diamond et al., ApJ, 347, 302; Faison & Goss, AJ, 121, 2706). Faison & Goss were able to map the opacity variations, which can exceed 0.8 in optical depth, across the face of the source and confirmed that structure on size scales of order 10 AU exist in the ISM. How such small-scale structure originates and is maintained in the neutral ISM is not well-understood.

Zwaan et al. (1997)

30 20 10 0 30

this work 2

1

12 3

this work

20 10 0

18

8

9

10

Figure 4: The HIMF for the low-luminosity KISS HI sample. The filled squares represent the HIMF calculated from the (1/Vmax) method for the sample, where all the upper limit HI masses have been included by using the value of the upper limit to determine bin placement. Error bars are 1-. The bins are chosen such as to maximize the number of galaxies within them while still producing a minimum of 5 evenly-spaced HIMF points. Of course, each of the upper limits may actually belong to any of the bins below that in which it was placed, and the true low-mass end slope may be steeper than implied by the filled squares. Thus, the extreme case was also investigated where all the upper-limit data points represent galaxies with HI masses which place them in the lowest mass bin present in the sample. This second HIMF is represented by the open stars. Two other HIMFs from HI blind surveys are shown for comparison; open circles are from Zwaan et al. (1997), while open squares are from Rosenberg & Schneider (2002). The lower panels show the HI mass distributions used in computing the KISS HIMFs. The upper histogram corresponds to the number of galaxies used to compute each of the points given by the filled squares, while the lower one corresponds to the open stars. The unshaded portions of these histograms represent upper-limit "detections", while shaded areas represent true detections. (Courtesy: Janice Lee)

terms of LB or MHI. The HI properties of the sample follow: (i)The sample includes true dwarf g a l a x i e s , a s w e l l a s l a rg e r, h e a v i l y extincted, edge-on spiral galaxies. This is reflected in the broad distribution of HI line widths (39 ­ 311 km s-1, mean = 139 km s-1, uncorrected for inclination). (ii) The range of HI gas richness for the sample (as defined by MHI/LB) is the same as in previous HI surveys of latetype galaxies. They report weak anti-cor-

relations between gas-richness and both metallicity and blue luminosity. This is consistent with previous results for different samples of dwarf galaxies. (iii) Using the models of Ferrara & Tolstoy (MNRAS, 313, 291), their galaxies are shown to have a wide range of dark-to-visible mass fractions (0 < Mdark/Mstars+gas < 300). (iv) The median HI gas depletion time-scale for this sample increases from ~5 to ~13 Gyr when a metallicity-

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1.6

H 109

levels result in line emission at radio frequencies.

This team measured the H125 (3.4 GHz) & H109 H137 (5.0 GHz) lines from S88 at C109 He109 He137 Arecibo. Fig. 5 shows their 0 spectrum of the H109 line, 5003 5005 5007 5009 5011 5013 plus the H137 line, He109 Frequency ( MHz ) Figure 5: The 5-GHz, H109 recombination line from S88. Also seen are , C109 , and an adjacent the H137 line, He109, C109, and an adjacent line due to heavier line due to heavier elements elements (Courtesy: Murray Lewis) (Fig. 6); singly ionized ele0.3 ments heavier than C (e.g. C109 Mg, Si, Fe and S), may 0.2 contribute to the line emisHe109 S, Mg, etc sion. The total integration 0.1 time for this spectrum was 0 only 10 minutes on-source. In the same program, recom-0.1 5011.0 5 0 1 2 . 0 bination lines were detected 5010.0 Frequency ( MHz ) from six planetary nebulae. Figure 6: A detail from Fig. 5, showing the He109 line, C109, and the The sensitivity offered foladjacent line due to heavier elements (Courtesy: Murray Lewis) lowing recent adjustment of the telescope primary surface The data of Zauderer et al. (AJ, in press) gave a hint of a detection of promises fruitful observations to come.
0.8

between the objects. The project stretches across a number of radio astronomical disciplines, including pulsar search and polarimetry, multi-frequency full-Stokes continuum mapping, and HI & OH spectral-line mapping. Several approaches to constraining the distances of PSR J1907+0918 and the SNR are being attempted, including deriving their rotation measures (RMs), and searching for HI absorption by clouds situated in front of the SNR. In respect of the OH lines, the 1720-MHz transition was recorded as well as the 1665- and 1667-MHz lines; this often shows maser emission where a SNR is interacting with a neighboring interstellar cloud. The L-band S-band continuum maps confirm that the SNR possesses well defined shell structure. All continuum maps were scanned parallel both to R.A. and Dec, and a basket-weaving algorithm used to eliminate scan-to-scan systematics, producing images such as Fig. 7. Such Stokes-I maps will be used to extend our knowledge of the SNR spectrum. The distributions of the other Stokes parameters will soon be derived. Polarimetry on PSR J1907+0918 yields an RM of +730 rad m-2.

Flux ( K )

Flux ( K )

Zeeman splitting, but with only the VLBA and phased VLA in the VLBI array at the time, this detection was marginal. The objective of the present experiment was to image the HI absorption toward 3C 138, this time with sufficient sensitivity to confirm or refute the tentative detection of Zeeman splitting in their earlier observations. The VLBI array consisted of the VLBA, the phased-VLA, the GBT, and Arecibo. High Sensitivity Recombination Line Measurements I n J u l y 2 0 0 2 , Ye r v a n t Te r z i a n ( C o rnell), Murray Lewis (NAIC) & Arecibo REU summer students, Laura Chomiuk (Wesleyan), Stephanie Morris (Chicago) & Danielle Moser (Illinois) observed recombination lines from interstellar clouds at C- and S-band. One nebula, S88, coincides with a compact red object, is associated with a thermal radio source, and is embedded in a complex molecular cloud. Several molecular species have been detected from its vicinity. The ioni z e d p l a s m a o f t h e n e b u l a u n d e rg o e s recombinations that at high quantum

Are SNR G42.8+0.6, SGR 1900+14 and PSR J1907+0918 connected? The supernova remnant (SNR), G42.8+0.6, seems a typical, faint, shelltype SNR, but has two unusual neutron The OH 1665/1667-MHz data cube stars projected just outside it. One is the soft-gamma repeater, SGR 1900+14, reveals a small-diameter absorption patch a magnetar with 5.16-s pulses in the X-ray. The other, J1907+0918, is a young pulsar discovered at Arecibo while searching for radio pulses from SGR 1900+14. It is possible that the SNR marks the birth-place of either, or both, of these neutron stars. Sadly, distances to all 3 are rather uncertain. Snezana Stanimirovic (Berkeley), Laura C h o m i u k ( We s l e y a n ) , Ramesh Bhat (Haystack), Dunc Lorimer (Jodrell Bank), Chris Salter (NAIC) & Dejan Urosevic (Belgrade) are Figure 7: The continuum emission at 1640 MHz in the field of SNR looking for connections G42.8+0.6. (Courtesy: Laura Chomiuk)

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H2O and OH in a Diffuse Cloud along the 0.0 Line of Sight to W51 David Neufeld (Johns -0.2 Hopkins), Michael Kaufman (San JosÈ -0.4 State), Paul Goldsmith (NAIC/Cornell), David -0.6 Hollenbach (NASA Ames) & RenÈ Plume -0.8 (Calgary) have com-1.0 bined the first detection 0 60 -20 20 40 of water vapor in a diffuse cloud with extensive Velocity (km/s) Arecibo OH observations Figure 8: The four OH transitions for the absorption patch against the interior of SNR G42.8+0.6; 1612 MHz ­ blue, 1665 MHz ­ green, 1667 along the same line of sight. These observaMHz ­ red, & 1720 MHz ­ black. (Courtesy: Laura Chomiuk) tions are particularly projected against the SNR interior. This valuable because the absorption lines of appears to be slightly larger than the 3both molecular species appear optically arcmin beam, has a radial velocity of +18 thin in the 6 km s-1 feature towards the km s-1, and a narrow velocity width. The bright HII Region. Although the region reality of the feature was confirmed via of massive star formation is estimated to several 5-min on-off measurements for be at 6.5 kpc, the diffuse cloud is likely all 4 OH lines (Fig. 8). The cloud exhibits relatively close to us. curious line ratios, far from the expected 1:5:9:1 for thermal equilibrium; relative The particular importance of observto that at 1667 MHz, the 1612- and 1665- ing these two species together is that they MHz lines are both significantly stronger provide a test of laboratory measurements than expected. No line was detected at of a key chemical reaction in dense inter1720 MHz, although studies at this fre- stellar clouds. This is the dissociative quency are a struggle due to RFI. The 1612-, 1665- & 1667-MHz absorption (0,0) 1.05 lines are narrow indeed, with a FWHM of 3.5 km s-1. Examining the HI distribution 1 over the same velocity range as the OH absorption, a feature is seen that matches 0.95 the structure of the SNR remarkably well. -1 The velocity frame at +19 km s shows 0.9 edge-brightened HI emission following the SNR continuum perimeter. Were the (+7.2, -11.8) gas associated with the SNR to have a 1.05 -1 VLSR of +18 km s , a simple model of 1 galactic rotation would yield a (far) distance of 11 ± 3 kpc. If this were truly to be the distance to G42.8+0.6, it would lie 0.95 far beyond SGR 1900+14 (distance ~5.7 kpc from its X-ray spectrum), although it 0.9 could be consistent with the distance of 0 5 10 PSR J1907+0918, for which the distance VLSR (km/s) estimate is 7.8 (-1.08, +0.89) kpc.
0.2
Flux/Continuum Flux Flux/Continuum Flux

recombination of the molecular ion H3O+, which has channels resulting in OH + H2, H2O + H, and finally atomic oxygen with hydrogen in a combination of atomic and molecular forms. The branching ratio of this reaction plays a critical role in determining the abundance of H2O (which can be a major cloud coolant), and of OH, which is thought to lead to O2 via neutral-neutral reaction with O. Previous SWAS observations have indicated low H2O abundances. However, suppressing this channel did not seem viable given the measured abundances of other species, including OH and O2. Laboratory measurements have yielded contradictory results for the branching ratio, with Williams et al. (MNRAS, 282, 41) indicating that 0.05 of the reactions yield H2O, while Jensen et al. (ApJ, 543, 764) and Neau et al. (J. Chem Phys., 113, 1762) measure a water branching fraction equal to ~0.2. A r ec ib o o b s e r v at io n s ( F ig . 9 ) y i el d an OH column density of 8 â 1013 cm-2, while SWAS gives 2.5 â 1013 cm-2 for H 2O . T h e o b s e r v e d a b u n d a n c e r a t i o , N ( H 2O ) / N ( O H ) 0 . 3 i n t h e 6 k m s -1 feature, is significantly larger than an upper limit derived previously from
(-4.2,+2.2)

Brightness Temperature (K)

(-11.0, +6.7)

0

5

VLSR (km/s)

10

Figure 9: Arecibo OH spectra at 4 different positions in the vicinity of W51 (offsets in arcmin). The red, green, and bluecurves show the 1612-, 1665- & 1667-MHz transitions respectively; the 1720-MHz transition (short dashes, top left) was only reliably detected towards the (0,0) position due to RFI. (Courtesy: Paul Goldsmith)

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ultraviolet observations of a similar d i ff u s e c l o u d i n f r o n t o f t h e s t a r H D 1 5 4 3 6 8 . T h e p r e s e n t r e s u l t s a rg u e against the very low branching ratio for H2O formation, but the variations suggest that there may be a contribution in one or both of these clouds from a warm gas component having temperature >400 K, which allows an enhanced rate of neutral-neutral reactions. More detailed models including photodissociation and self-shielding processes are included in a paper accepted by Ap J. "Dead" OH/IR Stars Six "dead" OH/IR stars (i.e. examples that no longer have detectable 1612-MHz masers) have been found by Murray Lewis (NAIC) while reobserving the set of Arecibo OH/IR stars following a 12yr break. However, the identification of "dying" stars would be greatly expedited if other diagnostics were known. With this end in view, Murray & Dieter Engels (Hamburg, Germany) have looked for clues in the observational record of FV Boo (15060+0947), a currently "dying" star. They find that the earliest premonition for most occurs with the presence of a strong 22-GHz maser close to the stellar velocity. This is followed in time by the development of similar OH, usually 1665-MHz features, which are rare. The 1612-MHz spectrum of FV Boo defines a stellar velocity of -9 km s-1, and an expansion velocity of 11 km s-1. Yet
FV Boo = 15060+0947 1612 MHz Flux ( mJy ) 100 1665 MHz

in 1985 it had a strong 1665-MHz line at -10.5 km s-1, whose emission stretched to -14.5 km s-1, as well as a 10.7-Jy, 22-GHz feature at -13.4 km s-1, while its 1667MHz features were in close accord with those at 1612 MHz. A 10-mJy residual of the 1667-MHz line was still present in July 1999, though this disappeared within the month. It was succeeded in March, 2000 by new 1667-MHz emission over a velocity range about the stellar velocity, a pattern that has persisted ever since. Its water feature is now at -10.9 km s-1. Water masers at velocities such as those of FV Boo would be quenched in a normal, spherically-symmetric circumstellar shell. Moreover, there should be little OH at these velocities, as water molecules would be protected from UV degradation by the outer dust shroud, and OH is quickly processed into water again. So the presence of water and 1665-MHz features in this dying OH/IR star point to it having already by 1985 passed from the phase in which dust couples photon momentum into the circumstellar shell, to the alternate state in which massloss is only supported at a much more modest rate by stellar pulsation: also, it had already passed on to the subsequent state in which the outer dust shroud has been so diluted by its ongoing expansion without replacement, that interstellar UV is degrading molecules in its new, inner shell. Further, the persistent absence over 1999-2002 of any mainline emission at velocities < -13.2 km s-1, though this was present in 1985, points to a continuing and expected decline in both the current expansion velocity and mass-loss rate, as well as to the obliteration of most of the molecules that previously existed around -14 km s-1. Fig. 10 shows the 1612-MHz spectrum from July 1999, whose peaks are now generally < 20 mJy. The 1665MHz spectrum from

July 2002 is overlaid, together with positions for the strong 22-GHz water masers seen in July 1987 & June 2002. An Arecibo Survey of Extragalactic Formaldehyde In Oct 2001 & Apr 2002, Willem Baan (ASTRON/Westerbork), Peter Hofner & Esteban Araya (UPR-RP) conducted a C-band survey of extragalactic forma l d e h y d e ( H 2C O ) a t A r e c i b o . T h e 6 c m H 2C O t r a n s i t i o n h a s b e e n r e p o r t e d toward over 15 extragalactic sources (e.g. Baan, Haschick, & Uglesich, ApJ, 415, 140) in both absorption and emission. Most of the known extragalactic absorbers present broad absorption lines reflecting the large-scale molecular disk rotation, but at least three (LMC, M31 & NGC 5128) present narrow absorption features indicating the presence of foreground molecular clouds in the outer disk of thes e galaxies . M ore interes ting are the sources exhibiting H2CO emission. Currently, only four Galactic sources are known to be 6-cm H2CO emitters; one shows quasi-thermal emission (OrionKL), while 3 present masers (NGC 7538, Sgr B2 & G29.96-0.02). In contrast, 10 extragalactic masers have been reported, their nature seeming to differ significantly from Galactic examples. E x t r a g a l a c t i c H2 C O m a s e r e m i s s i o n i s many orders of magnitude the stronger and reveals details of the molecular and excitation environment in the nuclear regions of galaxies, providing clues as to the nature of such regions on the relevant size-scales. Baan, et al. have observed the H2CO (110-111) transition (0 = 4829.67 MHz) toward 63 extragalactic objects (VHEL = - 2 3 5 t o 4 5 0 0 0 k m s- 1 ) w i t h t h e 3 0 5 - m telescope. The sample comprises, 1) earlier detected sources, particularly the tentative detections from Baan et al., 2) ultra-luminous FIR galaxies known to have OH megamasers, plus those with OH absorption, and 3) nearby FIR galaxies, in particular spiral galaxies. Also observed simultaneously was the H110 recombination line (0 = 4874.16 MHz), towards a sub-sample of 54 sources.

0 -24 -16 -8 0 LSR Velocity ( km/sec ) Figure 10: The 1612-MHz spectrum for FV Boo from July 1999. The 1665-MHz spectrum from July 2002 is overlaid (light line), together with positions for the strong 22-GHz water masers seen in July 1987 & June 2002. (Courtesy: Murray Lewis)

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Figure 11: (Left) Measured 4.86-GHz Gain versus Dome Azimuth. (Right) Measured Gain versus Zenith Angle. Filled vs. open symbols represent two different epochs. Calibrators at Dec > 25° are represented by triangles, while those at < 25° are shown by squares The relatively low gain obtained towards north-setting sources is marked with an arrow. This asymmetry was taken into account during calibration. (Courtesy: Esteban Araya)

over 30 years of effort. With the launch of the Chandra X-ray Observatory and the availability of new or significantly upgraded radio telescopes (Parkes, GBT and, of course, Arecibo), this pursuit has accelerated and in the past year several more associations have been reported (e.g. Camilo et al., ApJ, 571, L41, and references therein). Following striking recent Chandra imaging of SNR G54.1+0.3 (Fig. 13), Fernando Camilo, Eric Gotthelf, Jules Halpern, Nestor Mirabal (Columbia), Dunc Lorimer (JBO), Ramesh Bhat (Haystack), Daniel Wang, & Fangjun Lu (UMass) used Arecibo to discover pulsations from PSR J1930+1852, a young, energetic pulsar at the SNR's center with a period of 136 ms (Fig. 13). A full report is in Camilo et al. (ApJ, 574, L71). The morphological and spectral properties of SNR G54.1+0.3 revealed by Chandra (cf. Fig. 13) leave no room for doubt as to the presence of a central pulsar. However, it is vital to measure its period (which Chandra could not do) and period derivative, and thereby determine its (characteristic) age and spindown luminosity. Earlier, Gorham et al. (ApJ, 458, 257) used the pre-upgrade Arecibo to search this SNR for a pulsar, but without success. Could this be due to the pulsar "pointing the other way"? Determining the "beaming fraction" of pulsars is of great interest, for example to constrain the Galactic population of young neutron stars. A deeper search seemed in order. Fernando et al. tried this on Aug 29, 2001, but it was spoiled by RFI, so they tried again on Apr 29, 2002, this time with success. The WAPP was used in its 3-level, 16-bit mode, recording 256 lags across a 100-MHz band every 295 sec for each polarization at a center frequency of 1180 MHz. This frequency was used rather than the more standard 1475 MHz as the telescope gain is higher at the lower frequency, as are pulsar fluxes). Data was recorded for a full 2.7-hr transit, including 8 min when the source could not be tracked, being too close to the zenith. The data were reduced in standard fashion, and a signal found with a period of 136.8 ms and maximum

Figure 12. The H2CO 110-111 spectrum toward NGC 520. are marked with crosses. (Courtesy: Esteban Araya)

The observations used standard position switching. During the survey, 17 different calibrators were observed to get 29 estimates of telescope gain at different azimuths, zenith angles and epochs. Fig. 11 shows the gain versus azimuth and gain versus zenith angle curves. All data reduction was made in CLASS. The observations have resulted in a total of 10 sure or tentative detections. T h e s e c o m p r i s e 4 H 2C O a b s o r b e r s , 5 H2CO emitters, and one H110 emitter. They have not been able to confirm all t h e t e n t a t i v e H 2C O e m i t t e r s p r e s e n t i n the literature. However, some prominent sources such as the OH-MMs Arp 220 and

IRAS 15070+0727 have been confirmed. Fig. 12 shows the new detection o f H 2C O a b s o r p t i o n toward the galaxy NGC 520. While RFI was found within the H2CO bandpass, the 9-level sampling contained this within 9 channels (channel width 12 km s-1) and it did not affect the rest of the bandpass. Artifacts due to RFI Willem et al. also report the first detection of H110 from the giant HII region NGC 604 in the galaxy M33, p l u s a w e a k H 2C O a b s o r p t i o n t o w a r d this source. This work is currently being prepared for publication. Discovery of a Young, Energetic Pulsar in the Crab-Like SNR, G54.1+0.3 To understand the birth properties of neutron stars (e.g., periods, magnetic fields, velocities) and the physical conditions and evolution of SNRs, it is important to discover and study pulsars associated with SNRs. Until recently, only a handful of such associations were known, despite

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signal-to-noise ratio of 20.7 at dispersion measure (DM) = 308 pc cm-3. The pulsar was confirmed 9 days later, by which time the barycentric period had increased by 0.6 sec, providing a crude measure of the period derivative. Using this, they then reduced archival ASCA X-ray data, detecting a consistent period from the SNR center (Fig. 14). This confirms beyond doubt that the new pulsar, PSR J1930+1852, is the central point source seen by Chandra (Fig. 13). Using the pulsar position thus known t o a r c s e c a c c u r a c y, p l u s s u b s e q u e n t pulse arrival times measured at Arecibo f r o m s ev er al 4 5 - min in teg r atio n s , th ey obtained an accurate period and period derivative. From these they derive a characteristic age of 2900 yr (estimating an actual age for the pulsar and SNR in the range 1500-6000 yr), spin-down luminosity of 1.2 â 1037 erg s-1 and surface magnetic dipole field strength of 1.2 â 1013 Gauss. This places PSR J1930+1852 in the group of 10 pulsars with the highest known values of spin-down luminosity and lowest apparent ages. Curiously, it has spin parameters virtually identical to those of PSR J11245916, a pulsar recently found in SNR G292.0+1.8 (Camilo et al., ApJ, 567, L71). However, the respective SNRs are very different: G54.1+0.3 is "Crab-like" --a classic compact synchrotron nebula powered entirely by the pulsar, while G292.0+1.8 is a composite SNR--a pulsar wind nebula embedded in a large, bright shell of stellar ejecta. The discovery of the young pulsar powering G54.1+0.3 will enable a better understanding of SNR energetics. Fernando et al. have also begun radio and X-ray timing studies to characterize the rotational stability and emission mechanisms of the neutron star. However, the broader significance of this discovery lies in the realization that young pulsars can be extremely faint: with a flux density of 0.06 mJy at 1180 MHz and luminosity (for a distance of approximately 5 kpc) of about 1 mJy kpc2 at 1400 MHz, this pulsar (plus a few recently discovered

Figure 13: Chandra ACIS-S3 image of SNR G54.1+0.3, color-coded by energy: 1.0-2.0 keV (red), 2.0-3.5 keV (green) and 3.5-8.0 keV (blue). The bright central point source corresponds to the pulsar, and is surrounded by an arc and apparent jets resulting from interaction of the relativistic pulsar wind with the ambient medium (see Lu et al. ApJ, 568, L49). This image also demonstrates the trend of X-ray spectral softening from the inner to the outer regions of the nebula, likely caused by a combination of synchrotron cooling and adiabatic expansion of the shocked wind material. (Courtesy: Fernando Camilo)

Figure 14: Average pulse profiles of PSR J1930+1852. Two periods are shown in each panel for clarity. Phase zero is arbitrary in both cases. Top: 8.75 hr of Arecibo WAPP data at 1180 MHz. Note the broad emission "wings"; bottom: X-ray ASCA GIS data at 2-10 keV. (Courtesy: Fernando Camilo)

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ones) is at least an order of magnitude fainter than previously known young pulsars. Thus it is probable that several more such pulsars await detection, beaming at us below previous thresholds--in some cases likely reachable with the new radio telescopes. The lesson is clear: maximum-effort searches of wellselected pulsar candidates (in some cases indicated by new X-ray observations) should become the norm. Pulsars still being discovered by the Upgrade Drift-Scan Surveys F o l l o w i n g p r e l i m i n a r y e ff o r t s ( s e e N e w s l e t t e r N o . 3 3 ) , D u n c L o r i m e r, Maura McLaughlin (JBO), Kiriaki Xilouris (UVA), Don Backer (UCB), Jim Cordes (Cornell), Andy Fruchter (STScI), Zaven Arzoumanian (Goddard) & Andrea Lommen (Amsterdam) have been processing drift-scan data taken via the 430-MHz Carriage House towards the end of the Arecibo upgrade (199698). The data were collected by Kiriaki using the PSPM in areas allocated to the Berkeley/Cornell & NAIC/STScI groups, and have good sensitivity to nearby msec (and even sub-msec) pulsars, as well as the population of low-luminosity normal pulsars. The data are being processed on COBRA, a 180-node Beowulf cluster at Jodrell Bank, using Fourier transform procedures to search for periodic sig nals, plus algorithms designed to detect

individual pulses. So far, 850 deg2 of sky have been successfully processed, and 33 pulsars detected, 10 of which are new. H i g h l i g h t s o f t h e n e w d i s c o v e ries include a 5.79-ms pulsar at high Galactic latitude and a 55.7-ms pulsar in the Galactic anticenter. The pulse profile for the latter is shown in Fig. 15; a preliminary phase-connected timing solution suggests that it is a solitary object with an estimated spin-down age of ~2 Myr and a magnetic field of only ~2 â 1011 Gauss. If this is confirmed by further observations it places this pulsar in a fairly unique position in the periodperiod derivative diagram. An interesting note about this object is that it was discovered using the 430-MHz Dome receiver, rather than the more traditional Carriage House. To our knowledge, this is the first pulsar discovered with the 430MHz Gregorian receiver. It is hoped that follow-up timing of all the newly discovered pulsars will begin towards the end of the year, by which time the data processing will be complete. The number of pulsar detections is expected to be about 50. Further details can be found at http: //www.jb.man.ac.uk/~drl/drift. PSR J1752+23 ­ A "Bursting" Pulsar Slavko Bogdanov (Penn State), Tom SoltysÌnski (Szczecin U, Poland) & A l e x Wo l s z c z a n ( P e n n S t a t e ) h a v e completed the initial study of PSR J1752+23, a pulsar discovered in the Penn State/Arecibo surveys and characterized by unusually long nulling periods. The pulsar was observed as part of the timing campaigns in 2000 & 2001 and, in a more dedicated fashion, during the early months of 2002. Consecutive single pulses were recorded over 1-2 hr intervals at 430 MHz with the PSPM and at 1400 MHZ with the WAPP. PSR J1752+23 spends 70-80% of its time in a "quasi-null" state. The "onstates" occur once every 400-600 periods and last, on average, for ~100 periods. A compilation of 10 such "bursts" is shown in Fig. 16. Clearly, the bursts are quite similar in shape and duration, with the average characteristics described by

the top profile. Their decay into a null state is quite reasonably described by a t e-t/ function with ~45 sec. Properties of the pulsar 's bursting behavior do not seem to depend on the observing epoch or frequency. With its P=0.409 s andP= 0.6 â10-15 s/s, PSR J1752+23, is a fairly typical member of the slow pulsar population. However, it does not follow the standard assumption that nulling pulsars are mostly found close to the hypothetical "death line" in the P-P diagram. Similarly, it does not conform to the common description of nulling, because it switches off gradually, rather than suddenly as observed for typical nulling pulsars. Another difference in PSR J1752+23 is that a very low-level, pulsed emission (3 detection in a 2.5-hr

Intensity

0.0

0.5 Pulse Phase

1.0

Figure 15: The full pulse profile of the 55-7-ms pulsar discovered from drift scans using the 430-MHz Gregorian receiver. (Courtesy: Dunc Lorimer)

Figure 16: Examples of bursts of pulsed emission from PSR J1752+23 at 430 MHz. The top burst profile is the sum of 40 bursts lined up using a 6 trigger level. The solid line is the best fit of a function of the form t . e -t/ t o t h e d e c a y i n g p a r t o f t h e b u r s t . ( C o u r t e s y : Alex Wolszczan)

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integration of null pulses) is continuously present during the null state. Finally, the astonishing morphological similarity of the on-states and their very similar time s ca l e s a n d r e p e t it i o n r a te s a r e u n i q u e among nulling pulsars. The above emission characteristics of PSR J1752+23 make it exceptional among the pulsar population. Since neither the timing nor pulse profile morphology data indicate any pulse arrival time and/or pulse shape variability that could be due to or bital motion or pre cessional beam wobble of the pulsar, it appears most natural to assume that its unusual properties are related to the pulse emission mechanism. As these properties may provide new, useful constraints on the emission process, observations of PSR J1752+23 will be continued, including polarization measurements and simultaneous observations at multiple frequencies to achieve a possibly complete phenomenological description of this fascinating object. A New Binary Millisecond Pulsar in a Globular Cluster After analyzing 1.5 TB of L-band WAPP search data taken on 10 globular clusters this past summer, Scott Ransom (McGill/ MIT), Ingrid Stairs (NRAO), Jason Hessels (McGill), Vicky Kaspi (McGill), & Dunc Lorimer (JBO) report a new binary millisecond pulsar (MSP) in M71 -- the first pulsar discovered in this cluster. This brings the total of new MSPs discovered by this project to four (two new pulsars in M13 and one in M5 were detailed in Newsletter No. 34). M71A is an eclipsing 4.8-ms system (see Fig. 17) in a 4.2-hr orbit around a very low-mass companion (> 0.03 M¤) -- typical of the burgeoning ~ class of eclipsing binary MSPs. Observations in Aug 2002 showed that the new MSP discovered in M5 (M5C) also undergoes eclipses, with an orbital period of 2.1 hr, and has a companion with a mass > 0.04 M¤ . Addi~ tionally, an orbital solution was found for the new MSP, M13D, giving an orbital period of 14 hr, and a more massive companion (> 0.17 M¤). Scott et al. are ~
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to reveal their identities , des pite many efforts to find low-energy counterparts. The large positional uncertainty of -ray sources in the energy range 100 MeV ­ 10 GeV, which can be greater than 1° across, is a major stumbling block in this endeavor. This team approached this problem by targeting potential hard X-ray counterparts to these sources, discovered by Roberts, Romani & Kawai (2001) in an ASCA survey of EGRET error boxes. Recently, Mallory et al. observed two of these X-ray sources, AX J1907.4+0549 & AX J2021.1+3651, from Arecibo using the WAPP at 1.4 GHz. This has resulted in the discovery of a young (characteristic age 17 kyr), energetic (spin-down luminosity 3.4 â 1036 ergs s-1), 104-ms pulsar in the direction of AX J2021.1+3651 with a 1425-MHz flux of only ~0.1mJy. The pulse profile of PSR J2021+3651 is shown in Fig. 18. Given the rarity of such young, energetic pulsars, and the small size of the Arecibo beam (FWHM ~ 3.3´ at 1.4 GHz), an association with the X-ray source is highly probable. Furthermore, PSR J2021+3651 lies in the error box of the hard-spectrum, low-variability, -ray source, 3EG J2021+3716 (also known as GEV J2020+3658 & 2CG 075+00). This association, along with the high inferred s p i n - d o w n l u m i n o s i t y o f t h e p u l s a r, strongly suggests that PSR J2021+3651 emits pulsed -rays, a very exciting pros-

Figure 17: (Top) Two cycles of the average pulse profile of the new eclipsing MSP in globular cluster M71. The grey-scale beneath the profile shows the duration and intensity of the pulsar signal in time. An eclipse is clearly visible. The 1.4-GHz WAPP data were obtained in June 2001. (Courtesy: Scott Ransom)

currently making regular timing observations using the WAPP, which also allows them to search for new pulsars that may become visible due to scintillation. Finally, together with Paulo Freire (NAIC), an additional 1.5 TB of search data have recently been taken on 12 other globular clusters. After processing, they will have searched all globular clusters visible from Arecibo and within 50 kpc with unprecedented L-band sensitivity. They expect to find several more MSPs in the process. A Distant Gamma-Ray Pulsar? Mallory Roberts (McGill/MIT), Jason Hessels (McGill), Scott Ransom, Vicky Kaspi (McGill/MIT), Paulo Freire (NAIC), Fronefield Crawford (Haverford) & Dunc Lorimer (JBO) report the discovery of a young pulsar in the error box of a high energy -ray source known since the days of the COS B satellite. Most of the sources observed by COS B and EGRET have been reluctant

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Intensity Pulse Phase F i g u re 1 8 : T h e 1 . 4 - G H z p u l s e p ro f i l e o f P S R J2021+3651. The error bar shows the 1 uncertainty. (Coertesy Jason Hessels)

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pect as there are currently only a handful of confirmed -ray pulsars. The DM of PSR J2021+3651 is 371 pc cm-3, by far the highest known in the Galactic longitude range 55° < l < 80°. Using the new Cordes & Lazio (2002) electron model of the Galaxy, this DM corresponds to a distance of ~12 kpc, putting it at the far edge of the outer spiral arm. Such a large distance implies that, if PSR J2021+3651 is the low-energy counterpart to GeV J2020+3658, it is extremely efficient at producing -rays. Planned X-ray and infrared studies of PSR J2021+3651 may be able to further constrain the distance to the pulsar. Planned timing observations of PSR J2021+3651 over the course of the next year, will allow an accurate determination of the position, which, combined with an approved Chandra observation, will be a definitive test of the association of the pulsar and the X-ray source. Pulsars in the Galaxy, M33? Maura McLaughlin (JBO) & Jim Cordes (Cornell) have completed their search for isolated, dispersed radio pulses from the spiral galaxy M33. This was undertaken in the hope of detecting Crab-like objects emitting "giant" pulses, or pulses with 100 ­ 1000 times mean pulse strengths. The search resulted in the detection of several pulses at high DM which are consistent with signatures of astrophysical origin and may well be pulses from extra-galactic pulsars. Sadly, because of the difficulty in distinguishing astrophysical signals from terrestrial RFI, it is not currently possible to ascertain the origin of the pulses. However, the results of the search, available at http: //www.jb.man.ac.uk/~mclaughl/M33, should be very useful for planning future single-pulse searches with the Arecibo feed-array, which will allow anti-coincidence tests, and with the SKA, whose sensitivity and field of view will revolutionize our understanding of the transient radio sky.

Timing the PSR J2016+1947 Binary System The binary pulsar PSR J2016+1947 was found in 1990 in an intermediate galactic latitude search using the Arecibo 430-MHz line feed. The pulsar (period = 64.94 ms; DM = 34 cm-3 pc) was confirmed in Dec 1997, and observed from the end of 1997 to that of 1999. Due to its very long orbital period, and a lack of coverage for about half of the orbit, it has been very difficult to determine its timing parameters. The best timing solution, still marred by possible rotation count ambiguities, yields an orbital period of ~635 days, and an eccentricity of ~0.0015. Due to a large gap in observations in 1998, it is not clear whether there is genuine phase connection, and a second full orbit must be observed to clarify this. A companion mass of 0.29 M¤ was derived assuming a pulsar mass o f 1 .3 5 M¤ and an in clin ation of 90 ° . The pulse profile of PSR J2016+1947 is quite narrow, and it is detected with high signal-to-noise even in 3-min integrations. Given the object's low DM, the prospects for high-precision timing are good, especially given imminent Arecibo capabilities such as the new Lband receiver and the ability to observe pulsars with a 400-MHz total bandwidth via 4 WAPPs. The PSR J2016+1947 system promises to excel as a tool to test the Strong Equivalence Principle (SEP), the basic foundation of General Relativity (GR). This principle requires the universality of free fall, even for objects that have very significant gravitational self-energies. Thus, both PSR J2016+1947, with its very large (negative) self-gravitation energy of about 15% of the total mass (depending on the equation of state for cold matter at high densities), and the white dwarf companion, with its neg ligible self-gravitational energy, should fall in the Galactic gravitational field with the same acceleration. However, if the assumption of SEP is wrong, as postulated in many alternative gravitational theories, (i.e., if || = |1 - mI/mG| 0, where mI and mG are the inertial and gravitational masses of the pulsar), the

accelerations for the pulsar and the white dwarf will be different. The effect will be similar to that of a neutral atom under a strong electric field, which causes different accelerations on the nucleus and electrons, with the net effect of a polarization of the atom. In atomic physics, this is known as the "Stark" effect, the resulting polarization is more intense as the electrons are further from the nucleus. The equivalent gravitational "Nordtvedt" effect on a MSP/white-dwarf binary produces an increase in the eccentricity of the system, and this too becomes more pronounced for wider orbits. The timing project being made by Paulo Freire (NAIC), Stuart Anderson (Caltech), JosÈ Navarro (Schlumberger) & Rick Jenet (Caltech) is aimed at confirming the eccentricity and characteristic age of PSR J2016+1947. If these are confirmed, then the figure-of-merit for 2 a Stark test, PB /e (Arzoumanian, Ph.D. thesis, Princeton), is 5 times higher for PSR J2016+1947 than for any other system with known eccentricity and large characteristic age. Using all the binary systems that pass this criterion, a value of || < 0.004 was obtained (Wex, A&A, 317, 976). This could improve by a factor of 5 using the PSR J2016+1947 system. The Lunar Laser Ranging (LLR) experiment tests SEP violation in the weak field limit, predicted (among others) by the Brans-Dicke theory. The test now being carried out at Arecibo i s q u a l i t a t i v e l y d i ff e r e n t a s i t p r o b e s the strong field regime, it can impose, among all known gravitational tests, the most stringent constraints on the tensor-bi-scalar theories of gravitation (Esposito-FarÈse, Pulsar Timing, GR & the Internal Structure of Neutron Stars, 13). These are among the very few viable alternatives to GR, and predict virtually the same results in the weak-field limit probed by Solar System tests like LLR. Only when strong fields are involved do differences in behavior like SEP violation become, in principle, observable.

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J1740+10 Freq=1.4100 GHz, BW=8.000 MHz Calibrated with CL #1 but no bandpass applied
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Figure 19 Fringe (POSSM) plots after using pulsar gating for J1740+1000, a weak (~mJy) pulsar, between Arecibo and 9 VLBA stations. The top of each panel shows the visibility phase, while the bottom shows the amplitude, as a function of frequency (averaged in time). (Courtesy: Shami Chatterjee)

Frequency Dependence of the Pulsar Scintillation Arc Phenomenon Readers of this Newsletter & ApJ will know that Dan Stinebring (Oberlin) and his collaborators continue to dig deeper into the phenomenon of "scintillation arcs" that they stumbled upon through Arecibo observations of January 1999. These arcs arise from interference between various parts of the spatially coherent pulsar image. The basic data behind the arcs are recordings of successive pulsar spectra, producing what is known as a dynamic or primary spectrum. Stinebring, et al. have used both the AOFTM and WAPP spectrometers to good effect (and look forward eagerly to a multi-WAPP era). Their observations, made both on-site and from Oberlin, are generally in the range from 430 MHz ­ 2.2 GHz, with a maximum bandwidth of 100 MHz, typically 1024 spectral channels, and a 10-sec dump time. They find that dynamic spectra are remarkably rich in features when explored with Arecibo's sensitivity. Dan analyzes a dynamic spectrum by taking its two-dimensional power spectrum, forming what is known as a secondary spectrum, in which the scintillation arcs appear as sharply delineated parabolic arcs. These correspond to a quilted or cross-hatch pattern back in the primary (dynamic) spectrum. What causes these arcs? Although this is not yet fully clear, the essential ingredient is interference between a bright central core of the image and a more extended halo around this, both caused by scattering off of electron density variations in the ISM. A simple model with all the scattering taking place in a thin screen along the line of sight allows them to relate observable features of the scintillation arcs to the screen location. In addition, this predicts that the curvature of the arcs in the secondary spectra should be frequency dependent, scaling as 2. In June 2002, Dan, with Oberlin students, Henry Barnor, Daniel Berwick, Alex Hill & Aaron Webber, descended on the Observatory for a two-week observing run. Its focus was to test the fre -

PSR J1740+1000; A Pulsar of Special Interest Zaven Arzoumanian (GSFC), Shami Chatterjee, Jim Cordes (Cornell) & Maura McLaughlin (JBO) are continuing their ongoing studies of PSR J1740+1000, discovered in one of the Arecibo-upgrade 430-MHz drift-scan searches. This pulsar is of interest as i t s s m a l l a g e a n d l a rg e h e i g h t a b o v e the Galactic plane (derived from its DM) imply a very large velocity. Since its discovery, monthly timing has been undertaken in support of high-energy and VLBA observations. J1740+1000 is weak and shows strong scintillation, with an average L-band flux of ~1 mJy. The VLBA alone lacks the sensitivity to detect this pulsar with sufficient signalto-noise for astrometry. Fortunately, Arecibo, with a collecting area some 15 times that of the entire VLBA, can provide the necessary boost in sensitivity. In March 2002, Arecibo joined the VLBA for a successful phase-referenced observation, and strong fringes were detected for the pulsar on all baselines to Arecibo (Fig 19). It is expected that s ub-milliarcs ec astrometry will be possible, and a proper motion (and possibly a parallax) can be

measured via future observations. Such pulsar velocity measurements, especially those of the high-velocity tail of the pulsar velocity distribution, are important for constraining SN physics and the initial velocity "kicks" imparted to neutron stars, and for pulsar population models. PSR J1740+1000 has also been observed with the Chandra X-ray O b s e r v a t o r y, r e v e a l i n g a f a i n t p o i n t source with a thermal spectrum. Early results of spectral fitting suggest that the neutron star is either unusually cool (compared to other pulsars with similar timing ages), or more distant than estimated via its DM (which would imply a still-greater pulsar velocity). No pulsations at the radio-derived 154-ms period are evident in a timing analys is of the X-ray data. Further investigations of the X-ray properties of PSR J1740+1000 will be important for understanding neutron star cooling and the relationship between luminosities and beaming geometries of radio and high-energy emissions.

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2250.0

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-- inverted versions of the original parabolic arc -- at the higher observing frequencies. Finally, the arc curvature does indeed s cale w ith w avelength as 2, i m p o r t a n t c o n f i r m a tion of the basic scenario for arc formation: scattering dominated by a thin screen along the line of sight and interference between the core and halo of the pulsar image. They plan to continue multi-frequency monitoring of this time variable phenomenon for the half dozen or so pulsars that most clearly exhibit the e ff e c t . D a n p a r t i c u l a r l y w an ts to tr ack in d iv id u al sub-arc features over a range of closely spaced observing frequencies to see if these shift around in position as predicted by their simple model.

Frequency (MHz)

sion heights and polar cap locations of the emission cones and could prove to be a powerful tool to study pulsar emission geometry. Observations of most bright, Arecibovisible pulsars with multi component profiles were made, largely at 432 & 1175 MHz, with a few also being observed at 2250 & 5000 MHz. Basic data reduction has been largely completed, and detailed analysis for modeling the emission geometry is underway. Preliminary results show the following: (i) For pulsars in common with the 3 2 0 - M H z G M RT o b s e r v a t i o n s ( e . g . PSRs B1237+25 & B1821+05), all the new components can be reproduced at 432 MHz, strongly arguing their genuineness. The advantage of Arecibo for such a study is demonstrated, as components that were barely detectable in the GMRT data are fairly easily seen at 432 MHz! At higher frequencies, as components come closer together in longitude and pulsars become weaker, it is somewhat more difficult to detect weak components. (ii) The frequency evolution of some components is quite remarkable; e.g., for PSR B1821+05 (Fig. 21) the 1175MHz profile appears to show the main conal components (labeled II and N) significantly shifted with respect to the core component. However, detailed analysis shows that component N corresponds to one of the newly detected, weak components at 432 MHz, which has become much stronger at 1175 MHz. The emission corresponding to component III at 432 MHz is also detected at 1175 MHz, close to where it is expected, but much weaker than N. This illustrates the possibilities for wrong identification of corresponding conal emission components at different frequencies. (iii) For several other pulsars, new emission components have been detected; in some cases these are seen clearly in the average profiles (e.g., Fig. 22). The final results should provide a more complete picture of the emission cones for many of the pulsars.

2.6

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Figure 20: A primary and secondary spectrum pair for an observation of PSR B0834+06 at 2.2 GHz. The WAPP spectra were obtained over a 100-MHz bandwidth (1024 frequency channels) and an effective integration time of 10 s per spectrum. The vertical striping in the (upper) primary spectrum arises because individual pulses are highly variable in strength and only 8 pulses are included in each spectrum. The secondary spectrum (lower panel) shows a broad parabolic scintillation arc that is composed of several distinct subarcs. The left side of the scintillation arc was brighter than the right not only at this frequency but at 0.43, 1.17 & 1.40 GHz too, and for 2 weeks of observations in June 2002. The cause of this asymmetrical brightening (seen for other pulsars, and which varies over a timescale longer than 2 weeks) is not known. (Courtesy: Dan Stinebring)

quency dependence of arc curvature, and to explore the arcs at frequencies above 430 MHz where most of their previous observations had been taken. The trip was highly successful, and they left Arecibo carrying a large quantity (~500 Gbytes) of high-quality spectra for 10 strong pulsars. A month of analysis back at Oberlin has led to several results. First, the scintillation arc phenomenon is found over the entire frequency range probed. In fact, some of the most interesting results were obtained at their highest frequency of 2.2 GHz (see Fig. 20), where the very low system temperature and relatively clean RFI environment contributed to signalto-noise ratios of >1000:1 in the dynamic spectra. Second, the arc phenomenon is more sharply defined at higher frequencies than at low. They often see "subarcs"

The Emission Geometry of Pulsars Yashwant Gupta (NAIC/ NCRA, India), Ramesh Bhat (Haystack) & R.T. Gangadhara (IIA, India) have made single-pulse observations of a sample of bright, well-known pulsars to carry out a detailed study of radio-pulsar emis sion geometry. This was motivated by the work of Gupta & Gangadhara, (ApJ, 2002, in press, & ApJ, 555, 31), where a new method for analyzing single-pulse data to determine the total number of emission components is described, and used to detect new emission compo nents for several pulsars from 320-MHz GMRT data. From these detections, they showed that the pulsar emission region contains multiple hollow emission cones surrounding a central core beam. Further, the conal beams show systematic retardation and aberration effects. This provides a new way to estimate the emis-

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Phase Amplitude

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from preliminary analysis for PSRs B1237+25 & B1821+05 provide evidence for a substantial emission height for the core radiation. Further, it appears that this height may decrease monotonically with increasing frequency; at 320 MHz, it is ~1200 km above the neutron star surface and drops to ~600 km at 2250 MHz. These estimates are significantly larger than those in existing models, where the core beam is thought to originate very close to the neutron star, whose radius is ~10 km. A detailed analysis of all the data should be extremely interesting in this context. Final results from this work should provide significant new constraints for the emission geometry of pulsars -- and h e n c e f o r t h e p o s s i b l e e m i ssion mechanisms.

Pulse Phase (deg)

Figure 21: Emission profiles for PSR B1821+05 at different frequencies. The arrow with "N" indicates the location of one of the newly detected components, which is easily visible at the two higher frequencies. (Courtesy: Yashwant Gupta)

Figure 23: Mass-mass diagram for the PSR B1534+12 system. Labeled curves illustrate 68%-confidence ranges of the theory-independent "DD" relativistic parameters. The filled circle denotes the component masses expected in GR. A kinematic correction for assumed distance 0.7±0.2 kpc from the Taylor & Cordes (ApJ, 411, 674) DM model has been subtracted from the observed value of Pb; the uncertainty on this kinematic correction dominates the uncertainty of this curve. A slightly larger distance of 1.02±0.05 kpc removes the small apparent discrepancy between the observed and predicted values of Pb. (Courtesy Ingrid Stairs)

(iv) For most of the pulsars, 432-MHz emission-height estimates for the conal components (with respect to that of the core) range from ~200 to ~1000 km, while their transverse locations range from ~0.2 to ~0.7 of the distance from the magnetic axis to the edge of the polar cap. (v) Using the longitude locations of the core and conal components at multiple frequencies, it is also possible to extend the retardation-aberration method to uniquely constrain the emission heights for the core beam. Results
Average Profile for PSR B2002+31 at 1175 MHz using Arecibo 250 Pulse Amplitude 245 240 235
New New

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Figure 22: Examples of newly detected components for PSR B2002+31, with arrows marking their locations. (Courtesy: Yashwant Gupta)

The Timing of PSR B1534+12 Ingrid Stairs (NRAO), Steve Thorsett (UCSC), Joe Taylor (Princeton) & Alex Wolszczan (Penn State) have recently submitted a paper describing long-term t i m i n g o f t h e r e l a t i v i s t i c d o u b l e - n e utron-star binary pulsar B1534+12. The observations span 4 yr pre-upgrade, and 4.5 yr post-upgrade. Post-upgrade data were taken with the Princeton Mark-IV coherent-dedispersion system, which minimizes timing systematics due to dispersive smearing in the ISM, in parallel with the PSPM. Tests show that the Mark-IV data are essentially free of the timing systematics that appeared in the pre-upgrade filterbank 430-MHz data, allowing the modern 430-MHz data to be fully incorporated into the relativistic timing fits. DM derivatives are required both pre- and post-upgrade, and the best-fit values are significantly different, implying changes in the structure of the ISM between Earth and pulsar. Like PSR B1913+16, B1534+12 provides stringent tests of the predictions

of general relativity. For B1534+12, the measured values of the advance of periastron, the time dilation parameter and the shape of the Shapiro delay agree with the predictions of GR to within 0.05% (see Fig. 23). The observed orbital period derivative, affected by the relative acceleration of the pulsar system and the Solar System Barycenter, provides a greatly refined measurement of the distance to the pulsar: 1.02 ± 0.05 kpc. The masses of the two neutron stars can also be derived from the timing solution. It is now clear that the observed recycled pulsar is significantly less massive than its younger companion, contrary to initial expectations from most binary evolution theories in which mass is transferred from the companion to the older neutron star. Solar System Studies Ellen Howell The 18-cm OH Lines of Six Comets

T

he 18-cm OH lines are a valuable diagnostic of conditions in comet comae. The brightness of the OH lines is related to the total OH production in

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Lewis & Alice Hine (NAIC) have recently observed OH in 6 comets at Arecibo: C/1999 S4 LINEAR, C/1999 T1 McNaught-Hartley, C/2001 A2-B LINEAR, 153P/Ikeya-Zhang (2002 C1), C/2000 WM1 LINEAR, & C/2002 F1 Utsunomiya. Spectra were obtained at 1612, 1665 & 1667 MHz with a spectral resolution of 68.6 m s-1. Whenever the observed nucleus-centered lines were strong, 7-point maps (spacing ~ 4.1 arcmin) were also made. Due to the pointing limitations at Arecibo, Comet C/2000 WM1 LINEAR was observed when the heliocentric velocity gave small values for the predicted inversion. However, the observed spectra show very interesting line shapes which provide valuable constraints on the inversion models. Monte Carlo models were run for both day- and night-side emission over a range of OH parent velocities and quenching radii using 2 different models for the inversion (Despois et al., A&A 99, 320; Schleicher & A'Hearn, ApJ 331, 1058). For each date, the best-fit model to the data was used to estimate the OH production rate (Tacconi-Garman et al., AJ 364, 672; Schloerb & Gerard, AJ 90, 1117). Best-fit models and spectra are illustrated for 3 of the comets in Fig. 1. When maps

Figure 1: 1667-MHz OH nucleus-centered spectra for Comet C/1999 T1 McNaught-Hartley (M-H), C/2001 A2-B LINEAR, and C/2002 F1 Utsunomiya (U). Solid lines represent observed spectra, while dashed lines represent best-fit models. (Courtesy: Ellen Howell)

the coma, and the line shape contains information on the gas outflow velocity. -doublet transitions responsible for the 18-cm OH emission are due to a process in which OH molecules are excited from the ground state by strong solar UV lines and then decay radiatively. This may cause the -doublet levels to be either inverted or anti-inverted depending on the comet's heliocentric radial velocity. OH lines appear in emission amplifying the cosmic background when the levels are inverted, and in abs orption agains t this background when they are antiinverted. Moreover, variations in the OH excitation across the coma, due to differences in heliocentric velocity for molecules moving toward and away from the Sun, may also lead to a distortion of the line shape (Greenstein Effect) which must be accounted for in models of the emission. In extremely high-production comets, -doublet inversion may also be affected by collisional excitations between the levels. Collisions re-balance the population and thereby quench the inversion

produced by the UV excitation effect has been well observed in comets, but in more typical, production rate comets, the deg quenching has not been well measured, though it is thought to decrease with the square-root of the production rate. OH emission maps resolving the comet coma offer a way to characterize the degree of collisional quenching, as well as characteristics of the OH coma such as outflow velocity or asymmetry. The Arecibo telescope is well suited to resolving the coma with mapping observations at high sensitivity and high spectral resolution. Amy Lovell (Agnes Scott), Ellen Howell (NAIC), Pete Schloerb (FCRAO), Murray

. This bright lower ree of

Figure 2: 1667-MHz OH spectra as calibrated flux versus cometocentric velocity (solid line) for Comet WM1 LINEAR in Nov, 2001. The best-fit Monte-Carlo simulation (dashed line) employing the Schleicher & A'Hearn inversion model, with zero quenching radius and a parent outflow velocity of 0.6 km/s is also shown. (Courtesy Ellen Howell.)

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were made, they were consistent with small quenching radii for these low-production rate (1028 ­ 1029 mol s-1) comets. While the best fit for 153P/Ikeya-Zhang taken on 16 March, 2002 is consistent with a quenching radius of 50,000 km, all other maps yield quenching radii < 10,000 km. For every observation of Comet C/ 2000 WM1 (LINEAR), and for Comet 153P/Ikeya-Zhang taken on 23 March, 2002, transitional spectra of unusual shapes were seen, likely representing the transition from anti-inversion to inversion of the -doublet. Gases in different portions of the coma are moving at different heliocentric velocities, so the radio OH excitation is different at different positions in the coma. Since the two inversion models predict the zero amplification phase to occur at slightly different heliocentric radial velocities, simulations of such transitional spectra provide an opportunity to discriminate between the models. All transitional spectra treated here are only consistent with the Schleicher & A'Hearn inversion model. Typical spectra are shown in Fig. 2, along with best-fit Monte Carlo models. RECEIVERS AND RELATED Paul Goldsmith New Wideband Receiver for L-Band new L-band receiver is being assembled and initial laboratory testing completed. This unit is essentially the same as developed by NRAO for the GBT, and we thank NRAO engineering staff, particularly Mike Stennes, for their assistance. The receiver will cover 1.15 to 1.73 GHz, and should offer considerably lower noise and fewer resonances than the ex-SETI receiver (L-wide) that we have used at Arecibo since the Gregorian Upgrade was completed. A new feedhorn has been designed by GermÀ n CortÈs (NAIC), and is currently being fabricated at the NAIC Maple Avenue laboratory by Kurt Kabelac and Dave Overbaugh. It should offer nearly ideal

illumination of the reflector system. When the feedhorn is completed and tested, it will be sent to Arecibo for integration with the receiver. Because of the importance of this receiver for HI, OH, and pulsar observations, it will have to be thoroughly tested before installation in the Gregorian dome. At the present time, we expect this installation to occur in the first half of 2003. Low Frequency Systems An improved feed has been installed for 300­330 MHz; this is a design by Jim Breakall and Mike Jacobs (Penn State). Work has begun on design of a cooled receiver for 300­330 MHz. Once cooled, the receiver should have a lower system temperature than the previous system. This important band is plagued by RFI, but is valuable for pulsar work, continuum observations, and VLBI. 6 ­ 8 GHz Receiver Serious design work has begun on the 6­8 GHz receiver, which will be the final single pixel receiver to complete continuous frequency coverage from 1 to 10 G H z. J agadheep P andian, (a graduate student at Cornell), Lynn Baker (NAIC), and GermÀn CortÈs have been evaluating different designs for an orthomode trans ition for this frequency band, and are currently measuring a very promising finline device that was developed by G. Chattopadhyay (Cal Tech) and J. Carlstrom (Chicago). Our plan is initially to build a dual polarization single pixel system, but one which can in the future be upgraded to a dual beam system, with a Dicke switch to allow radiometric noise limited continuum observations. Tertiary Skirt We are continuing to evaluate options for system noise reduction by reducing spillover by means of a skirt (a mini-ground screen) around the periphery of the tertiary reflector. This will redirect spillover o ut o f th e d o me aper tu re an d o nto the cold sky. A number of discussions have emphasized the need for lightening the

proposed structure, and making it more resistant to winds and vibration encountered in hurricane conditions (even inside the Gregorian dome!). GermÀn CortÈs is updating his design, with input from a mechanical engineering consulting firm in Ithaca as well. Arecibo L-band Feed Array (ALFA) The logical next step for both spectroscopic and pulsar surveys is a focal plane array. During the past two years, NAIC staff and users have been engaged in development of the concept which has now evolved into ALFA, a 7 element dual polarization system covering 1225­1525 MHz. The front end is being built by CSIRO in Australia; it will comprise the feedhorns, dewar, dewar rotator, orthomode transitions, amplifiers, and DC bias supplies. Different feedhorn designs have been extensively analyzed by GermÀn CortÈs, and this study has resulted in the choice of TE11 mode stepped circular feedhorns, similar to those used on the Parkes Multibeam system. Information about ALFA is available at the web site http://alfa.naic.edu. The Arecibo Electronics Department under the leadership of Edgar Castro is developing the 14 channel LO and IF system, which will employ fiber optics links. For signal analysis, we will initially have a system with 7 Wideband Arecibo Pulsar Processor (WAPP) units. Bill Sisk and Jeff Hagen have been working hard to make these available for all pulsar modes as well as spectroscopy, and we are confident that this system will be up and running well in advance of arrival of the ALFA front end. In fact, 4 WAPP units should be available by early 2003, and as each covers up to 100 MHz bandwidth, it means that up to 400 MHz will be available for use with any single pixel system, either for pulsar or spectroscopic science. A preliminary design meeting with Graeme Carrad, Graham Moores, and Pat Sykes from CSIRO took place at Arecibo on September 12 and 13. The greatly enhanced capability of the multibeam system should become available after the middle of 2004. It
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Initial ALFA Extragalactic HI Consortium Meeting

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he National Astronomy and Ionosphere Center (NAIC) is building a 7-feed focal plane array at L-band (1225­1525 MHz) for the Arecibo 305-m telescope. The possibilities afforded by this instrument are tremendous. For example, extragalactic astronomers will benefit from the ability to perform extremely sensitive spectral-line observations over a wide area of the sky. Having at least ten times greater sensitivity than the Parkes multibeam system, the Arecibo L-band Feed Array (ALFA) will allow observers to study questions such as: Is there a limit to the column density of neutral hydrogen? How numerous are the extremely low luminosity (no luminosity?) gas clouds? Is there gas outside of galaxy clusters? What types of systems are associated with the Lyman-alpha, and damped Lyman-alpha systems? Do other galaxies have HVCs? Although ALFA will be open for individual project proposals, the importance of this instrument to the scientific community has led NAIC to encourage those interested in using it for large surveys to pool their knowledge and interest by forming consortia. The first meeting for those interested in using ALFA to explore extragalactic HI is planned for 15-17 March, 2003. Potential topics for consideration at this meeting include: A full description of the Arecibo Observatory and ALFA, including plans for both the frontends and backends of the system; Defining the major scientific goals of the consortium project(s); Discussion of the software/hardware needs for data processing; Issues involving data archiving and public access to ALFA data; Guidelines involving consortium membership. Those interested in attending the meeting should register online at http://alfa.naic.edu/extragal/meeting1/reg.html. Please note that due to housing constraints meeting attendance will be limited to 40 participants. Meeting registration closes January 17, 2003. will be so powerful that it is appropriate to consider new modes of operation, plausibly by groups of astronomers, in order to deal with the large volumes of data that will be produced. NAIC is thus encouraging formation of consortia to deal with some of the key areas of scientific use of ALFA. At the present time two consortia meetings are scheduled -- a pulsar consortium meeting will be held at Arecibo on 2-3 November 2002, and an extragalactic consortium meeting will be held on 15-17 March 2003. Additionally, a meeting for users intersted in using ALFA to explore Galactic phenomena is being considered for the spring of 2003. The topics to be discussed and the consortia themselves are described online (http://alfa.naic.edu). We strongly urge anyone interested to register their interest in the consortia and hopefully to participate in these meetings. You can join one of several consortia already proposed through the NAIC web site at the URL given above. Do check out the information on the ALFA web site and contact a NAIC staff member if you have any questions. From the Electronics Department Compiled by R. Ganesan Transmitter Parts Salvaged from Alaska Jon Hagen We lose a klystron about once a year and used to buy replacements from the manufacturer, Litton Industries, at a cost of about $220,000 each (in today's dollars). Around 1986, the BMEWS station at Thule (Greenland) was upgraded to a phased-array radar, and the Air Force gave us 16 surplus tubes. Just as we used up the last of those tubes, the Air Force finished the phased array at BMEWS site 2 in Clear, Alaska. This time we were given 14 tubes. In January VÌctor Iguina and JosÈ Vives went to the base at Clear, where they removed the tubes from the transmitters and prepared them for shipment. The tubes are now on site in Arecibo. In July, accompanied by Jon Hagen, they returned to Clear and filled a 20ft container with waveguide components, two driver klystrons, focusing magnets,

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he Observatory's 430 MHz transmitter dates back to the late 1950s, when the BMEWS (Ballistic Missile Warning System) was being designed. Our system uses the same type of power klystrons.

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VÌctor Iguina and moose visiting the BMEWS site in Clear, Alaska. (Photo by Jon Hagen)

vac-ion pump controllers, and other miscellaneous transmitter hardware. The radar at Clear, off the air for more than a year, was still 95% intact. Miles of WR2100 waveguide connect the three large search antennas (each covering a 40-degree sector) to the two transmitter buildings. Each search antenna used a fixed reflector, 165 ft high by 400 ft wide. The feeds in front of these reflectors rotated about a vertical axis in order to scan in azimuth. Horizontal cuts through the reflectors are therefore circular arcs, centered on the axis of the scanner. Feeds were provided for beams at two elevation angles, 3.5 degrees and 7 degrees. A missile would be seen as it passed through the lower beam, and then again as it passed through the upper beam. Once detected, the target would handed over to a tracking radar that used a fastmoving 85 ft dish. Each search antenna actually had two fixed horizontal rows of feeds, each with 100 side-by-side horns. Waveguides from each row of horns were routed to enormous rotating distributors ("organ pipe scanners") whose circumferences were about equal to the width of the row of horns. The two transmitter buildings together housed about 25 transmitters. Each transmitter was very similar to our Arecibo transmitter, using two klystrons in parallel. A mile-long access tunnel connected the transmitter
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buildings and then led to the coal-fired power plant. Receivers used parametric amplifiers with X-band pumps. Three of these BMEWS systems (Thule, Clear, and Fylingdales in England) were built at a cost of more than a billion (1960) dollars. Recently Installed Receivers The "X-band" receiver covering 8­10 GHz was installed in December 2001 and the "S-band High" receiver covering 3­4 GHz was installed in March 2002. For further information, the reader can r e f e r t o h t t p : / / w w w. n a i c . e d u / ~ a s t r o / RXstatus. New Receiver to Replace the Present L-wide Receiver A new receiver covering 1.15 - 1.73 GHz will replace the present L-wide receiver in the first half of 2003. The reader can refer to the article on page 21 of this issue. Final characterisation and calibration will be done at the Receiver Test Facility before scheduling the installation in the Gregorian dome. While awaiting the arrival of the new feed-horn from Ithaca, amplifier gain stability tests will be done in the laboratory.

Photo of the new L-wide receiver taken by Bill Genter when he led the assembly and the initial vacuum and cryogenic testing efforts.

RF-to-Fiber Converter for ALFA Front-end Edgar Castro has designed a complete RF-to-Fiber converter for the 7-beam, 14-channel ALFA receiver. The 1225­ 1525 MHz band is converted by a fixed o s c i ll a t o r t o a 3 0 0 - M H z w id e I F b a n d centered at 260-MHz. After filtering and amplification, the signal is routed to the integrated Anacom Fiber Optic Converter and sent down to the Control Room. A A picture of the prototype version that is currently being tested in the laboratory is shown below.

A picture of the prototype version of the RF-to-Fiber converter for the ALFA front-end that is being tested in the laboratory.

Filter Bank for L-Narrow Receiver A switchable filter bank was installed in early June, 2002 for the L-narrow

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receiver and is operational. It consists of (1) 1130­1530 MHz band-pass filter, (2) 1280 MHz high-pass filter and (3) 1370 MHz high-pass filter for each channel. If desired, either of the high-pass filters can be used in conjunction with the band-pass filter. Transmission plots can be seen at http://www.naic.edu/~astro/RXstatus/ Lnarrow.shtml. A New 430-MHz Receiver for Gregorian Dual-Beam Radar operations During Dual-Beam radar observations, the Gregorian Dome 430-MHz System is modified for transmitting up to 1 MW of pulsed power through the feed-horn. The turnstile junction acts as the isolating device between the transmit and receive paths, while additional receiver protection is provided by switching in a PIN-diode Monoplexer during transmit cycles. Following front-end Low Noise Amplifier (LNA) burn-outs with the cooled receiver, we have now built a new room temperature receiver front-end exclusively for radar observations. The problems of poor reverse recovery time and LNA failures have been prevented by using a high dynamic range balanced LNA from Angle Linear Inc. A diode limiter brought by VÌctor Iguina from Alaska has also been included between the monoplexer and the LNA. Documentation Lisa Wray has been working on improving the technical documentation on all receivers. Up-to-date information, including daily logs, can be accessed from http:\\www.naic.edu\~lwray. Education and Outreach Activities JosÈ Alonso/ Daniel Altschuler The 2002 Teacher Workshop he 4th àngel Ramos Foundation Workshop for Distinguished Science Teachers was held at the Arecibo Observatory from June 9 to 21, 2002. For the first time in the program, participants

Participants in the 4th Angel Ramos Foundation Workshop for Distinguished Science Teachers held at the AOVEF

were housed on campus at the new North Visiting Scientist Quarters (NVSQ, see article on page 25). By housing the participants on site, additional time was provided for discussion sessions and group work. It also eliminated the problem of commuting from a hotel. A total of 42 teachers (22 middle school, and 20 high school) participated in the workshop; these were selected from 200 applications. The 2002 program included a general tour of the Arecibo Observatory and a lecture by a member of the scientific staff. It also included observation of sunspots, planets and the summer constellations. The professional development program focused on the use of the Texas Instruments graphing calculator and its associated calculator based labora tory (CBL). Some of the activities included: ­Temperature and heat measurements; ­ Wa t e r q u a l i t y s t u d y ( p H , d i s s o l v e d oxygen, temperature and turbidity); ­Absorption and transmission of light by a solution; ­Rate of transpiration in plants;

­Study of sound (waveform, frequency and intensity); ­Study of motion (displacement, average speed, acceleration); ­Pressure (as a function of depth). Participants received equipment and training for activities that will allow them to carry out these and many other science experiments in their schools. The teacher workshop will include two follow-up sessions and school visits by members of the staff during the school year.

The recently installed solar exhibit at the AOVEF

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New Exhibits A new attraction at the Visitor Center is NASA's recently installed solar display. The interactive exhibit provides live images of the Sun from the Solar Helio-

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New North VSQ completed
Daniel R. Altschuler

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s you can appreciate from the photo (right), the Observatory now has a new building, located on the right hand side (driving in) of the entrance road. The dedicated efforts of engineer JosÈ N. Maldonado and of the construction crew ably lead by VÌctor Santiago made it possible to complete the building in time to house the participants of our recent science teacher workshops. With a capacity for 24 persons (double occupancy in each of 12 rooms) the Arecibo Observatory now has the ability to house about 40 visitors, and with the recently completed Learning Center to host small scientific or technical meetings. Indeed, in the upcoming months meetings related to ALFA consortia and a Radar Meteor Workshop will take place. We hope that these new facilities will enhance the Observatory's intellectual environment and that you will consider our facilities as a possible venue for a small meeting.

spheric Observatory (SOHO). Visitors can now enjoy spectacular views of the Sun at different wavelengths. The exhibit also provides additional animations and videos that illustrate different aspects of the Sun-Earth connection. The exhibit is bilingual and the solar images are displayed in a 42" plasma screen. This acquisition was made possible by a recent collaboration with the Goddard Space Flight Center (NASA).

related to the event. The Sun-Earth Day is an idea promoted by NASA, ESO and other organizations, in order to enhance our awareness of the Sun-Earth interaction. During this event, 540 visitors had the opportunity to observe sunspots and learn how the Arecibo Observatory contributes to our understanding of the sun-earth interaction.
JosÈ Gerena, the 2002 Teacher in Residence at AO.

Participants in the March 20, 2002 Sun-Earth Day.

Sun-Earth Day On March 20th, 2002, the Visitor Center participated in the Sun-Earth Day by providing special lectures and activities
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Teacher in Residence Sponsored by the National Science Foundation's Research Experiences for Teachers (RET), a summer position is awarded to a high school science teacher. The selected teacher participates in a research project and contributes to our outreach activities. Mr. JosÈ Gerena, a physics teacher from the Luis Mußoz MarÌn public school in Barranquitas, was selected as the 2002 RET. Mr. Gerena was engaged in the organization of the 2002 teacher workshop. He designed several experiments for the CBL laboratory interface that were implemented in the workshops this summer. He also pre-

pared the assessment tools that were used as part of the workshop evaluation. The àngel Ramos Foundation Visitor Center: Five years Vi s i t o r s o f a l l a g e s a n d f r o m m a n y countries continue to visit the observatory every year. Special visitors have included government officials (both from the U.S. and Puerto Rico), scientists and engineers from many research institu tions, including NASA. Since the opening of the Visitor Center in 1997, over 640,000 visitors have toured the facility. This figure represents an annual average close to 110,000 visitors, with children

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(mostly in the form of school groups and summer camps) accounting for 30 % of the visitor flow. Computer Department News Arun Venkataraman Wide-area Networking newly-inked agreement for Internet services with the University of Puerto Rico will boost local access speeds to DS3 (45Mbits/s) levels. With the decomissioning of the 10-yr old 56K link to the NASA Science Network at the end of August 2002, remaining services will be streamlined to use the OC3 fiber facility installed by Centennial last year.

and times of their scheduled block. Current schedules are available on the web at http://www.naic.edu/vscience/schedule. Real estate boom in the Control Room A new space-saving layout based on flatpanel LCD monitors permits six screens to be placed in the close vicinity of the Control Room observer, simultaneously displaying a wealth of information on the telescope and the progress of the experiment. Jeff Hagen has successfully deployed a "multicasting" technique to transmit telescope status packets on selected AO network segments, so that the current Control Room status screen can be viewed without connection overhead from virtually any networked location on site. The telescope status screen has itself been reworked and enhanced to display experiment-specific information. Servers and Storage Linux users familiar with `Mofongo', the dual-PentiumIII (1.2GHz) server which has proved its computational mettle against the Suns, will welcome the arrival of a dual-PentiumIV (2.2GHz) machine. (We had to pass on the cheaper 1.4GHz models). Wi t h d a t a t a k i n g r a t e s o f s e v e r a l MBytes/s becoming the order of the day, a new 1TBytes disk array was brought in to provide more parking space. More disk arrays will be added to ease the storage crunch and provide buffering for analysis prior to the (relatively slow) tape backup operation. Comings and Goings Nos Vemos, Ramesh Bhat Ramesh Bhat has recently left the Arecibo staff to work at Haystack Observatory as a Center for Astrophysics/MIT Post-Doctoral fellow. There, he will be working on LOFAR, the planned array of low frequency radio telescopes due to be built by 2008.
Yashwant Gupta

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Ramesh Bhat

Local-area Networking Residents of the new VSQs outside the AO gate will not lack for network connectivity -- the building plans included a comprehensive telecommunications layout, and fast ethernet fiber has already been installed. As in the other VSQs, a twisted-pair (RJ45) 10/100 ethernet socket will be provided. CIMA - The Control Interface Module for Arecibo Soon to be released: a redesigned User Interface (CIMA) now being tested by Jeff Hagen, incorporates an "executive" coprocess to improve performance and provide background functionality. One of the added functions is a concurrent data display based on IDL and controllable from a separate UI panel. Information on the new user interface is available online at http://www.naic.edu/~jeffh/ cima.html. Schedule reminders Following a request by last year's AO Users' Scientific Advisory Committee, a telescope schedule reminder service has been developed by Gomathi Thai. One-line e-mail messages are sent to the PI and Co-PI giving the Project ID, dates

Ramesh joined Arecibo in March, 2000 as the Cornell Post-Doctoral Research Associate. While here, he was an invaluable member of staff, helping considerably with development of the A r e c i b o p u l s a r p r o g r a m , c a r r y i n g f o rward his own research program, and acting as liaison to many of our outside pulsar observers. For the past two years, he was also the main organizer of the Arecibo REU program, and takes our deepest thanks for making such a huge success of this venture. We will all miss Ramesh very much and look forward to him coming back frequently both to observe and to visit. Muchas Gracias a Yashvant Gupta Sadly, Yashwant Gupta's sabbatical time at Arecibo has come to an end, and via Oberlin, Ohio, and Poland he is returning to the National Centre for Radio Astrophysics (NCRA) in Pune, India. Although only here for a little more than 10 months, Yash's contributions to Arecibo were extremely valuable. He provided considerable help both within our pulsar group and through his insights into radio as tronomy and ins trumenta tion in general. Additionally, Yash was

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Children of the Stars, the new book by Daniel R. Altschuler
by Chris Garcia

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n Daniel Altschuler 's first book, published by Cambridge University Press, he has managed to combine the discipline and scientific procedure of a scholarly text with the sense of wonder, mystery and inquisitive thought that anyone from a child to a PhD can relate to. The author uses simple terminology and a relaxed prosaic style that guarantees from the first chapter that the book will not alienate any reader. Altschuler`s ambitious non-fiction book deals with the origins of life on earth and possibly the universe. He balances precise historical documentation with commentary and theory to weave an engaging story that relates to immense and intriguing questions. Drawing from his background as a researcher, educator, and as the director of the Arecibo Observatory in Puerto Rico, (the world's largest radio telescope), the author offers the reader a highly educated viewpoint that is tempered with the wit and excitement of a man staring at a night sky. Children of the Stars flows in a series of chapters that present a story designed to make the reader look at the awesome conditions that came together to create the planets and eventually life in our galaxy. The chapters then offer a look beyond our planet. What lies in distant stars? Are we alone in the universe? Altschuler presents these questions with the reserve of a scientist, but allows for the innumerable possibilities that can be held in the vastness of space. The final chapter of the book comes as a surprise, especially given the work's road up to that point. The author lets our minds reach out to the very limits of the universe, then draws us in again to face the brutal reality of our own world's existence. Altschuler invites us to gaze into a "dark crystal ball" that confronts the reader with how pollution, overpopulation, and non-renewable resources are leading our planet to an untimely end. He reminds the reader that, while there is so much wonder and intrigue beyond our world, we need to preserve the source of the life force that feeds our desire to learn and explore. Children of the Stars is a very enjoyable read that is also educational and informative. Altschuler stresses early on in his work that he wanted to relate a story more than to compose a definitive text. As the author describes in the preface: "I have told the story as if I were telling a good (and patient) friend ..." With his use of humor, and giving clear analogies and comparisons, the book does feel like a conversation and not an instruction. The author 's experience as a university professor is a clear asset to the reader who is given multiple views and explanations meant to inform and enlighten. Children of the Stars never leaves the reader behind. The author is totally swept up in his voyage into the realms of science fact, but luckily, the reader is taken along for a fun and wild ride. Children of the Stars was also published in Spanish as "Hijos de las Estrellas". This article is reprinted from Business Puerto Rico. gracious enough to advise a student in the REU program during the summer m o n t h s . Ya s h , h i s w i f e R i c h a , a n d daughters Vishakha and Kritika will be missed both at the Observatory and on Calle Progresso. Adios a Snezana Stanimirovic In August, 2002, Snezana Stanimirovic l e f t t h e s t a ff a t A r e c i b o t o t a k e u p a position as a post-doctoral fellow at the Radio Astronomy Lab at the University of California, Berkeley. Snezana joined Arecibo as a post-doc in August, 1999, becoming a full staff member in 2001. While at Arecibo, she spent considerable time develop ing a package of IDL routines to reduce spectral line mapping data with the D i s h R a d i o A s t r o n o m y : Te c h n i q u e s and Applications", held at Arecibo in June 2001. She also took the lead in preparing the lectures from the school for publication; the book of the lectures will soon be appearing in the Conference Series of the Astronomical Society of the Pacific. We wish all the best to Snezana, and hope that she, Matthew, and Stinky enjoy Berkeley as much as we enjoyed their stay in Arecibo.
Snezana Stanomirovic

A r ecib o s in g le- p ix el r eceiv er s , as w ell as `friending' numerous outside observers and advising a number of summer students. She was a main organizer of the "NAIC/NRAO School on Single-

Nos Vemos NÈstor Aponte It is not easy to say goodbye to NÈstor Aponte, who has left the staff to take up a position on the faculty at Cedarville University in Ohio. After finishing his Ph.D. at Cornell under the supervision of Don Farley and Wes Swartz, NÈstor joined our
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Open Position(s) within the Arecibo Astronomy Group

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he National Astronomy and Ionosphere Center (NAIC) has at least one opening for a radio astronomer at the Arecibo Observatory. The vacancy can be filled at either the level of staff Research Associate or Post-doctoral Research Associate, depending upon the qualifications and experience of the successful applicant. A stimulating research environment is provided by approximately 25 resident staff scientists, postdoctoral fellows and senior engineers, as well as over 200 visiting scientists per year. In addition, physics and engineering faculty and students of the University of Puerto Rico have a cooperative research and educational association with the Observatory. Applicant whose research interests include any field of radio astronomy that can be exploited with the Arecibo telescope will be considered for the position. Besides conducting an independent research program, on-site staff scientists are expected to advise visiting scientists in all aspects of their observations, and to help define and implement improvements in equipment, observing procedures and data reduction. A PhD in astronomy or a related field is required. Staff Research Associates are appointed for a three-year period and may be reappointed for an additional three years, at which time promotion to Senior Research Associate may be considered. Senior Research Associates are appointed for a five-year period, with reappointment after review. Postdoctoral Research Associates are appointed for a two year period with possible re-appointment for a third year. The successful candidates will be employees of Cornell University, and hence eligible for all University benefits. Salary and benefits are competitive, attractive, and include relocation allowances. Details will depend upon the candidate's qualifications and experience. The Observatory provides lessons in Spanish, the language of Puerto Rico Evaluation of applications will continue until the position is filled. Please send a complete rÈsumÈ of academic, professional and personal data, a research plan, and the names and contact information for at least three references, to: The Director, National Astronomy and Ionosphere Center, Cornell University, Space Sciences Building, Ithaca, NY 148536801. EOE/AAE. team as a post-doctoral research associate in September 1998. NÈstor 's time here was shorter than we would have preferred but very productive. Some highlights of the work he carried out include: implementing the regularization technique that we use to obtain vector velocities from our line of sight velocity measurements in the F region; extending his energy balance studies for Jicamarca (this was his thesis work) to Arecibo and revisiting the OO+ collision cross-section problem; and finally, showing that including the predictions from the Sulzer and GonzÀlez coulomb collisions theory in the ISR least-squares fitting for Jicamarca is necessary for obtaining correct electron and ion temperatures. One of NÈstor 's skills was his ability to supervise and guide students, he always felt that was an important part of his job. In the fall of 2001 he took a semester off from working at Arecibo to teach in the EE department at Universidad del Turabo in Caguas, PR. We all wish NÈstor great success in his new position, he will be sorely missed but we hope to host him soon, now as a visitor and user (and maybe bringing students!). Adios a Qihou Zhou Qihou Zhou left Arecibo this summer for a faculty position at Miami University in Oxford, Ohio. He worked for the Atmospheric Sciences Department at Arecibo since Sept. 1991, primarily involved in studies of the lower ionosphere and thermosphere using incoherent scatter radar and optical techniques. During his tenure at the Observatory, Qihou was a prolific writer with more

Qihou Zhou

Nestor Aponte

than 40 papers to his credit (half of which he was first author), with topics ranging from traditional aeronomy, to meteor science and artificial intelligence. Probably Qihou's most valuable contribution to new science at the observatory is the study of details of micro-meteors as viewed by large aperture UHF and VHF radars. Much of the work contradicts theories of meteor flux distributions that evolved from measurements using conventional meteor radars. Qihou and collaborators proved that the echoes the Arecibo radar sees are primarily scattered from the head of the meteor rather than

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from the meteor trail. Once this work was established at Arecibo, other radar facilities like Millstone Hill near Boston and Sondrestrom in Greenland began similar research programs and verified what Qihou and his collaborators dis covered. There were several areas where Qihou Zhou made significant contributions to the research program at Arecibo. In addition to meteor science mentioned above, the technique he developed for D-region studies shortens the integration time by two orders of magnitude. His talents and contributions to Arecibo will be missed by many of us, but we wish him well at his new job.

all here, and we look forward to working together with him over the coming years. Early in 2003, he will be joined in Puerto Rico by his wife, Ranjana, and daughter, Akshaya, and we look forward to welcoming them here just as much as we now welcome Desh. Adios a Miguel F. Irizarry M i g u e l I r i z a r r y h a s l e f t t h e O b s e r v atory to take a position as an Electrical Engineer at the Autoridad de Energia Electrica. Miguel worked for the Arecibo Observatory for over one year in the Electronics Department. Along with a number of other projects, Miguel was responsible for the drive system maintenance and upgrade. It is with great regret we say good-bye to Miguel.

Avinash Deshpande

expect Desh to be with us in Arecibo for at least 3 years. With a freshly acquired B.Tech. in "Double E" from the Indian Institute of Technology, Kanpur, Desh joined the RRI in 1980 as an Electronics Engineer. H o w e v e r, h i s i n t e r e s t s s o o n m o v e d increasingly into astronomy. Over the next few years, he was heavily involved in the development of the decameterwavelength T-array (later synthesis telescope) at Gauribidanur, while he began his studies of pulsars, a central focus of his research work right up to the present day. Desh's astronomical interests have, however, spread widely over the years encompas sing image process ing, carbon recombination lines, HII regions, refractive interstellar scintillations, and the broader problems of the interstellar medium. His Ph.D. thesis was completed in 1988, and entitled "The detection and processing of pulsar signals at decametric wavelengths." From 1990-92, Desh passed a post-doctoral stay with the University of Tasmania in Australia, returning to be Assistant (from 1995, Associate) Professor in the RRI. Desh has also contributed much to the development of pulsar facilities at Ooty and the GMRT in India. Over the past three years or so, he has spent extended stays at New Mexico Tech and the Australia Telescope at Narrabri. At Arecibo, Desh will continue his pulsar and interstellar medium studies. However, he will also become the s c i e n t i f i c c o o r d i n a t o r f o r t h e A L FA (L-band) feed array, the front-end for which is currently under design and construction at CSIRO, Sydney. Desh's presence at Arecibo is a big bonus for us

Rob Wilson

Bienvenido a Rob Wilson We welcome Rob Wilson to the Arecibo Observatory as a post-doc for the next year. Rob recently completed his Ph.D. at Clemson University where he studied the atmospheric phenomena that cause quasi-periodic (QP) echoes from the lower thermosphere to be observed in VHF radars. Rob is supported by a CEDAR postdoctoral fellowship, for which he spent the first part working at Penn State University. He joins us along with his wife, Millie, and three daughters. Una cordial bienvenida a Avinash Deshpande The Observatory gained immensely on September 18th when Professor Avinash Deshpande (Desh) of the Raman Research Institute (RRI), India, joined us as a Senior Research Fellow in the R a d i o A s t r o n o m y D e p a r t m e n t . We

Miguel Irizarry

Buena suerte a Alexis EchevarrÌa Alexis resigned his position as an electronics technician to join a company in San Juan as a medical instrument technician. While at Arecibo, Alexis was responsible for all our communication systems, and became an expert in fiber optics. We wish him the best in his new endeavor.

Alexis EchevarrÌa

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Recent Colloquia August 12, 2002, Andrew Rivkin, MIT, "Water on Asteroids" July 12, 2002, Joe Burns, Cornell University, "Irregular Satellites: Dis coveries, Orbits and Origins" July 11, 2002, Riccardo Giovanelli, Cornell University, "Scaling Relations of Spiral galaxies and their Application to Cosmology" July 8, 2002. Victor Migenes, University of Guanajuato, "What about OH Megamasers?" June 27, 2002, Fernanda S. Tavares, University of Alaska, "Energy Deposition in the Middle and Upper Atmosphere by Lightning Generated Electric Fields" June 11, 2002, Jagadheep Pandian, Cornell University, "Methanol Masers: Tracers of Star Formation" J u n e 11 , 2 0 0 2 , D a n S t i n e b r i n g , O b e r l i n C o l l e g e , " Tw i n k l e , Tw i n k l e Little Pulsar" June 6 , 2002, Hendrik Linz, Astro. Inst. & Univ. Observatory Jena/ UPR, " T h e m a s s i v e s t a r- f o r m i n g r e g i o n G9.62+0.19 under the looking glass ­ Radio and infrared observations" May 30 , 2002, Dejan Urosevic, Belgrade Univ., "The Updated Sigma-D Relations for Supernova Remnants" May 17, 2002, Rachel Mastrapa, Univ. of Arizona, "Kuiper Belt Objects" May 9, 2002, Dunc Lorimer, Jodrell Bank, "S ear ching for Radio P uls ar s in New Targets and Old Data Sets" 11 A p r i l , 2 0 0 2 , A l b e r t o B o l a t t o , UC Berkeley, "Dwarf Galaxies at High Resolution: Probing Cosmology and Astrophysics with Molecular Gas" 4 A p r i l , 2 0 0 2 , Wi l l e m B a a n , ASTRON/NFRA, "LOFAR ­ the first of the new generation"

19 March 2002, Peter Backus, SETI Institute, "Project Phoenix: Progress and Plans" 18 March 2002, Eric Gawiser, U.C. San Diego, "Towards a Complete Picture of Damped Lyman Alpha Systems"

Single-Dish Radio Astronomy: Techniques and Applications
eds. Snezana Stanimirovic, Daniel Altschuler, Paul Goldsmith, and Chris Salter

T

his volume contains the lectures and poster papers presented at the first NAIC-NRAO School on Single Dish Radio Astronomy, which took place at the Arecibo Observatory in June 2001. The justification for this school was a combination of several factors. The first was the availability of both the Upgraded Arecibo 305-m telescope and the new Robert C. Byrd Green Bank Telescope (GBT) -- both major new tools for astronomers in the 21st century. The second was the feeling that `would be' users should benefit from a set of lectures whose breadth ranged from radio astronomy basics to in-depth discussions of some of the special techniques that have been developed over the years, but which are rarely described in print. Finally, we hoped that by including "hands on'' projects, we would give participants a real feeling for radio astronomical observations at centimeter and millimeter wavelengths. Our hope is that these lectures will prove to be useful for astronomers of varied backgrounds and experience who become involved with radio astronomy at different levels. This book will be available for purchase by December 2002 through the Astronomical Society of the Pacific Conference Proceedings Series -- http://www.astrosociety.org/pubs/cs/222-252.html

The NAIC/AO Newsletter is published three times a year by the NAIC. The NAIC is operated by Cornell University under a cooperative agreement with the National Science Foundation. Karen O'Neil and Jonathan Friedman, editors. Contact: koneil@naic.edu or jonathan@naic.edu; http:www.naic.edu.

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