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March 2000, Number 29

Note to Arecibo Telescope Users: Please be advised that when you publish results based on observations made at the Arecibo Observatory you must include the following acknowledgement: The Arecibo Observatory is part of the National Astronomy and Ionosphere Center which is operated by Cornell University under a Cooperative Agreement with the National Science Foundation.

Planetary Studies Don Campbell he fall of last year was a very active period for planetary studies with the first observations of the Galilean satellites of Jupiter since the early 1990's, the first observations of the Rings of Saturn with the upgraded ra-

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INDEX
Planetary Studies Highlights ........... 1 Space and Atmospheric Sciences .... 2 Thunderstorm Research .................. 6 Radio Astronomy Highlights ........... 8 Spectrum Coordination Agreement with Air National Guard ........... 1 6 AOVEF News .................................. 1 7 Employees of the Year .................... 1 8 Computer Department News ........ 1 9 Comings and Goings ...................... 1 9 Job Announcement ......................... 1 9 User Interface ................................. 2 0 Newsletter Guidelines .................... 2 0

Fig. 1: A delay-Doppler radar image of the Rings of Saturn (top) compared with a model delay-Doppler image (bottom) based on a Hubble Space Telescope image. (Courtesy Phil Nicholson)

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


dar system and the first Arecibo transmit/Arecibo receive observations of Titan with the new system. Just so that the outer planets did not receive all the attention there was also an extensive set of observations of the main belt asteroid Kleopatra. Although the radar system generally performed well, the observations were hampered by problems with the filament transformer for one of the transmitter 's klystrons. Despite great efforts by Tony Crespo (NAIC) and the maintenance staff all the observations were made with a transmitter power of approximately half the nominal one megawatt. New software was developed by Phil Perillat (NAIC) which, together with new hardware developed by the electronics department, enabled the rapid frequency switching over a wide band needed for the observations of Saturn's Rings and the long pseudo-random transmitter phase switching codes needed for delayDoppler observations of the Galilean satellites. The 10 MHz sampling rates needed for the observations of the Rings were achieved using the Caltech pulsar sampling system and, simultaneously, a new wide band sampling system being developed by Jean-Luc Margot (NAIC). Three groups made observations of the icy Galilean satellites with different objectives. Leif Harcke (Stanford) and collaborators investigated the use of the long pseudo-random codes to obtain delay-Doppler images for correlation with the distribution of different terrain types derived from spacecraft imagery. John Harmon (NAIC) et al. used the same technique with high time resolution to obtain distance and velocity measurements for orbit determination. In addition, Greg Black (NRAO) and collaborators measured radar cross sections at 13 cm wavelength, and attempted similar measurements at 70 cm, to confirm estimates from previous measurements of the properties of the upper layers of the icy satellites thought to be responsible for their unusual radio wavelength reflection properties. Unfortunately, the Observatory's 430 MHz

transmitter suffered a major klystron failure preventing the long wavelength measurements from being obtained. For the first time since the 1980's the declination of the Saturn system was high enough that Arecibo's tracking time exceeded the little over 2 hour round trip light travel time meaning that Arecibo could both transmit and receive for observations of the Rings and Titan. The difference was only 22 minutes so transmission occurred during the first 22 minutes after Saturn rose above Arecibo's horizon, and reception during the last 22 minutes of tracking time. This left almost 2 hours in the middle allowing interleaved observations of the Galilean satellites primarily for calibration of the Titan observations against the known cross sections of the satellites. Azimuthal asymmetries have been observed in optical observations of the Rings of Saturn and are thought to arise due to transient "wakes" resulting from the gravitational interaction between large and small particles. The objective of the radar observations was to search for clearer evidence of these wakes at the much longer radio wavelengths. Delay-Doppler observations of Saturn's Rings were made on six nights at a resolution of 15,000 km in range and a processing resolution of about 2,000 km in Doppler frequency (the Rings are about 280,000 km in diameter). Fig. 1 shows the resultant delay-Doppler image from averaging over the data from the six nights compared with a model delay-Doppler image based on a Hubble Space Telescope optical image of the Rings obtained almost simultaneously with the radar observations by Richard French (Wellesley, and one of the Arecibo observers) assuming that the relative radar backscatter cross-sections per unit surface area of the Rings mimics the optical albedo. The agreement is amazingly good if only the A and B Rings and not the tenuous inner C Ring are included in the model. As the only planetary satellite whose surface is obscured at optical wave-

lengths by an atmosphere, high-quality observations of Titan have been a major goal of the radar astronomy community. Observations by Muhleman et al. in the late1980s and early 1990s used the 70 m Goldstone antenna to transmit at 3.5 cm wavelength and the Very Large Array to receive the echo. The reported detections, although weak, indicated relatively high cross sections with considerable variability with longitude. Later, Goldstone monostatic observations and recent Arecibo transmit/Goldstone receive observations failed to show a clear detection. The Arecibo monostatic observations last November did result in a clear detection of Titan. The observations are currently being carefully calibrated as the measured cross sections and polarization ratios will provide basic information about Titan's surface properties. Observations of the main belt asteroid Kleopatra in November were very successful. Delay-Doppler images were obtained covering all longitudes allowing 3-D modeling of this very unusual asteroid.

Space and Atmospheric Sciences News Assistant Director 's Overview Donald Farley lot of interesting science is being done in what is now known as the Space and Atmospheric Sciences (SAS) Department at the Arecibo Observatory. Details on some of this work are given in descriptions below. I have only recently become seriously involved in the Arecibo program as the Assistant Director for SAS, and my aim here is just to outline some general points and the efforts that we have begun to encourage more participation by outside users in the Arecibo SAS research program. We would like to see more Ph.D. students and Postdocs in residence at Arecibo, and we welcome inquiries and suggestions on how to facilitate such collaborations.

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Arecibo has by far the most sensitive incoherent scatter radar (ISR) in the world, as is well known by readers of this newsletter. It also has an increasingly diverse and powerful collection of optical equipment, both passive (airglow) and active (lidars). The optical observing conditions are often surprisingly good. During my last visit, in January, I was surprised to notice that, although there were generally patchy clouds throughout the day, they usually disappeared at night, leaving very clear skies. A key strength of Arecibo is the ability to do combined radar and optical measurements, both with high sensitivity and resolution. This allows one to directly study both neutral and charged particle dynamics simultaneously, for example. All so-called "Class 1" UAFs (Upper Atmosphere Facilities) have this ability to varying degrees, to be sure, but the abilities of the Arecibo ISR are unique in several respects. It is a superb place to study the interactions of neutral and charged metallic layers in the E-region, helium layers in the topside, "ion rain" in the E-region, and much more. Some of the recent work is discussed further below. In the aftermath of Hurricane Georges (Sept. 21, 1998), the HF Ionospheric Interactions facility in Islote is being closed down. We hope to restore this capability using the main Arecibo dish to transmit. This, however, is neither a simple thing to do reliably and at a reasonable cost, nor with minimal disruption to the remainder of the scientific program. Some feasibility studies have been made, but additional ones are needed (and are planned) before we can develop a realistic proposal for a new HF facility. All this will take time. We recognize that there are many scientists anxious to do Ionospheric Interactions experiments at Arecibo, but they will have to be patient. We intend to undertake this effort only after careful planning. It is gratifying that the NSF is quite enthusiastic about restoring and supporting the Ionospheric Interactions program, assuming that this can be done for a price that the NSF can afford. The NSF
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recognizes, furthermore, that not all Ionospheric Interactions research is directly relevant to aeronomy, but ATM is willing to support it because it is good science -- the sort of science that National Centers are committed to doing. We lost one of two klystrons on the 430 MHz radar back in October, and there is no spare. We are continuing to operate (carefully!) with the remaining klystron, without too much degradation in data quality, but obviously we need working klystrons. It looks as though we can probably rebuild some of the old klystrons for "only" $70k or so each, however, which is good news. We will soon know whether or not the first rebuild attempt has been successful. Work is progressing well on finally getting the two-beam capability of the 430 MHz radar operational. The slotted waveguide is now in place, but we still need to get the power down to the feed in the Gregorian enclosure. There has been a significant upgrade in the lidar facility that is described elsewhere. Communicating with outside users We hope to improve our communication with the CEDAR community and other outside users in the months to come. We would like to see more use of Arecibo synoptic data and more on-site visitors from SAS scientists and students. As a first step in improving communications beyond what is done with this newsletter, we are working to improve our website. First of all, access to the NAIC site (www.naic.edu -- easy to remember) is now much faster because of the recent T1 line installation. Furthermore, there is now a separate SAS page (Home page Scientific Users SAS) that is under construction as this is being written. This page already has links to assorted information about the optical and ISR programs. In particular there is now a lot of new information about what World Day data are available and what the different observing programs do. Recently there has been a significant upgrade in how the F-region ion drift velocity data are analyzed, more specifically in

how the line-of-sight velocity measurements are converted into 3-D vector velocities. The process is called "linear regularization," and there is a link to a full description of the technique on the Incoherent Scatter page. We hope readers will consult our web site, and we welcome comments and suggestions for improvements. It is also worth pointing out that this newsletter is accessible from the NAIC site (see Scientific Users page), and some of the black and white figures in the newsletter are in color in the web version. Scientific Activities Craig Tepley Since the last newsletter was published in October, three scientific studies were done using the incoherent scatter radar, together with some optical observations as described below. The first was an experiment by John Mathews (Penn State) and Qihou Zhou (NAIC) to study "ion rain" (see Fig. 2), which ran for about 22 hours spread over four separate evenings in mid-November. During this same observing window, the second study, also by Zhou and Mathews ran our 47 MHz and 430 MHz radars in the so-called, "meteor mode" to study the Leonid meteor shower. This latter experiment ran for 54 hours spread over 6 days. These projects are described in detail below. The third study that took place during the current period was a Topside ionosphere run. This experiment involved Bob Kerr and John Noto (Scientific Solutions, Inc.) making optical observations of exospheric metastable He, and Sixto GonzÀlez and Nestor Aponte (NAIC) observing topside H+ and He+ with the radar, and ran in two campaigns in December and January. About 56 hours of radar time were allocated and used for this topside run, and in addition to this, about 24 hours of World Day time running the POLITE (Plasma Observations of Light Ions in the Topside Exosphere) experiment in December and January contributed to this Topside
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Moving day at the Optical labs. These photos show the move (left) and placement (right) of a 10â4 foot table, the last of three, within the Airglow lab. In the right-hand photo, Gilberto GonzÀlez, Oscar RolÀn, Joel Rivera, and Antonio PÈrez are shown lifting one side of the one ton table, while trusting supervisors JosÈ Jimenez and HÈctor Cruz (not shown) adjust the legs underneath. (Photos by Craig Tepley)

study. Although the optical component of these observations was severly affected by the poor weather experienced throughout the fall, the radar performed flawlessly (at half power). As is expected with increasing solar flux, the helium layer is becoming larger, reaching values of between 30 and 40 percent. During most of this past quarter, we observed the thermospheric neutral winds and temperatures by measuring the Doppler shifts and widths of the atomic oxygen, O(1D) 630 nm emission using one of our Fabry-Perot interferometers. This was done primarily to support World Day studies and the various visitor-initiated experiments during the period, but these data will also contribute to our extended data set of wind measurements, which we also provide to the CEDAR Database. Additional observations of the exospheric H emission line at 656.3 nm were made with our second Fabry-Perot during the Topside run, while Kerr and Noto used their own infrared Fabry-Perot interferometer to observe the metastable He emission at 1083.0 nm. In addition, we used two of Arecibo's photometers to observe oxygen 844.6 nm and H, which put all the pieces of the Topside puzzle together. That is, with the radar we can determine [H+],

[He+], and [O+], and with the optics we can measure the high-altitude distribution of [H], [He], and [O]. The goal is to understand how these major ions and neutral species interact during all seasons and levels of solar activity. Although the weather was less than optimum for about half of this three month period, we attempted these airglow observations on 21 nights, for about 10 hours each night. Our optical instrumentation runs, more or less, in an automatic mode and we sort out the data after the fact to filter the good results from those that were affected by the weather. By contrast, the instrument that Kerr and Noto have placed at Arecibo for these long-term studies requires liquid nitrogen cooling plus some other attention. Thus, either Kerr or Noto needs to be here to run it during their campaigns. Unfortunately, when they were here this last time to participate, the weather was not very cooperative. Another Topside study is scheduled for early March of 2000, and for this we hope to have better luck with the weather. Lidar operations were severely cut back as well due to poor weather from September until mid-December. Beginning on December 10th, a period of good weather allowed us to do some much needed receiver optimization and record

4 half-nights of mesopause potassium observations in a temperature mode of operation. We then observed for three nights January 19th and 20th (taking advantage of the lunar eclipse on the 20th) and on the 31st. These data are presently being analyzed to determine the structure of the temperature throughout the mesopause. During the week of January 10th an engineer from Continuum Laser installed our new Nd:YAG laser and upgraded dye laser. YAG laser power at 532 nm, used for Doppler-Rayleigh lidar studies of the stratosphere and mesosphere, was increased by 50% to 24 W. Our dye system, coupled to either a frequency doubler or mixer, can now reach wavelengths in the near-UV for the study of Ca, Ca+, Fe and other mesopause metals which have resonance features at these wavelengths. This was an UPR/EPSCoR-supported upgrade, which was done to promote studies of stratospheric ozone and tropospheric water vapor and aerosols, among other efforts. The Airglow Facility has also undergone a recent renovation. This project involved removing termite-infested gypsum board used in the walls, a reorganization of the observer area, and reorganization of the instrument room where our detection equipment is

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housed. We are implementing a plan to make more efficient use of space to address not only our own needs, but also those of our users who field their own equipment. We are also adding an optical filter characterization setup to maintain an up-to-date set of filter calibrations. Among other things, the reorganization involved moving several heavy optical tabletops between the Airglow and Lidar labs. The two photos (previous page) show the move of the last table, which weighed nearly a ton. Ion Rain and Leonid Meteor Shower Observations John Mathews, Pennsylvania State University In November, we carried out a set of ISR observations dedicated to the study of the horizontal structure of tidal ion layers, sporadic-E (Es), and ion-rain. The basic range/time resolution was 150 m per 0.16 seconds with a 0.4 deg/sec beam-swing (azimuth-scan) rate at an 8° zenith angle. The beam-swinging was between magnetic east and north with snapshot F-region ACF observations at each end-

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Fig. 3: An example of a meteor head echo, simultaneously observed by (a) the VHF radar at 46.7 MHz and (b) the UHF (430 MHz) radar. The meteor velocity is about 66 km/s. (Courtesy Qihou Zhou)

point. Although the radar was at halfpower due to the absent klystron and the tip of the line-feed had been removed in recognition of the proximity of Hurri-

Electron Concentration - 9/02/94
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cane (Wrong Way) Lenny at the cost of an additional dB of gain, sufficient signal-to-noise was available to see fine detail in layer structure during four different evenings of observations. In particular, the evening of 18 November was characterized by a highly vertically/horizontally structured layer located in the 88-95 km altitude region. The beam-swinging revealed that this "layer" was actually nearly vertical sheets of ionization with horizontal thickness as small as 1 km. Structures such as these were suggested in the 1989 AIDA Na lidar/ISR observations but the radar resolution utilized then was not sufficient to see such small-scale detail. The Na lidar was of sufficient resolution but was pointed at zenith. The advent of dualbeam capability will greatly enhance our ability to study these structures. The Leonids observations, also carried out in November, were designed to monitor both the micrometeor flux and the ionosphere -- important results have been obtained in both arenas. Micrometeor properties found as the result of

Log10(Ne) cm-3

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Fig. 2: This figure shows an example of "ion rain". These are denoted by the near-vertical striations in the electron density profile. (Courtesy John Mathews)

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these ongoing observations include accurate orbits, sizes, and deceleration as determined from the radar meteor headecho. Important determinations of meteor sputtering and other plasma processes have also been obtained. Also, Leonids observations from 1997 and 1998 have led to the identification of extrasolar meteors which are focused at earth orbit during the same time period as the Leonids. These observations were accomplished by continuously cycling between meteor-mode (50 secs/minute) and ISR-mode (10 secs/minute). The November 1999 observations yielded 53.5 hours of data of which 10 hours utilized only the VHF radar as the observatory was in a safe-mode due to the near-presence of Hurricane Lenny. The remaining observations were made with both the 430 MHz and VHF (46.7 MHz) radar systems. All meteor-mode observations utilized a 2 ms interpulse period while recording 300 range-gates at 150 m range-resolution. Preliminary results indicate that the AO peak of the Leonids occured during VHF radar-only "Lenny" period when the rate of larger meteors seemed higher than observed at any other time including the 1997 and 1998 Leonid periods. In any case these ongoing observations point to the relatively steady micrometeor flux (rather than meteor showers) as the major source of metals and dust in the MLT-region. The dual-frequency, common-volume observations also yield considerable information about meteor head- and trail-echoes. We look forward to Leonids 2000/2001 observations to complete this cycle.

rial at the meetings of our Users Group and Visiting Committee last October, I thought this Newsletter would be a good place to show some of their results, and a good opportunity to describe the current state of our capabilities for stratosphere-troposphere research at Arecibo. In a previous Newsletter (No. 26, Nov. 1998) I discussed the Autumn 1998 experiment that Petitdidier and Ulbrich performed at Arecibo. In that article, I also mentioned some of the meteorological related equipment these researchers fielded on-site for the several months of their campaign, such as a disdrometer to measure rain content and droplet size and an electric field meter. Petitdidier and Ulbrich were fortunate enough to not only experience several very active afternoons with thunderstorms, but they were also able to observe (albeit with limited instrumentation) while Hurricane Georges passed just south of the Observatory on 21 September 1998. This was an exceptional opportunity to study the structure of the lower atmosphere within a hurricane. Petitdidier and Ulbrich are still working with the complex hurricane data, and unfortunately I do not have material to show at this time. However, they have presented some of their thunderstorm work at various conferences and a portion of this I will now discuss. One objective of their research is to study the dynamical, microphysical, and electrical properties of tropical thunderstorms and their environment. A particular goal is to improve what we currently know of the exchange properties between the troposphere and the stratosphere in the presence of a convective system or hurricane. The circulation patterns within the vicinity of these large, columnar towers of convection that are often seen in the tropics is one mechanism by which minor species, such as NOx formed by lightning flashes, are transported vertically and penetrate the tropopause. As mentioned, Petitdidier and Ulbrich brought their own equipment to

Arecibo for their campaign, but they also used our UHF and VHF radars, as well as t he N ational Weather Service's NEXRAD system located in Cayey, PR, and balloon-borne radiosonde data. One interesting "visitor instrument" deployed was an electric field meter used to measure the field strength of the local atmosphere within a few kilometers near the ground, over a 5 km radius. This is a commercial product that senses abrupt changes in the field strength and direction, and can provide advance warning for potential lightning strikes that might pose a serious hazard at, say, a refinery or an airport. During operation, a gradual change in the direction (say, from negative to positive) of the electric field is first noted as a nearby storm is born. As the storm develops, the field quickly strengthens and abrupt changes caused by lightning discharges become more frequent and intense. For one particular storm, Fig. 4 shows the measured electric field, a portion of the data from the VHF radar, and the rainfall rate measured with the Clemson disdrometer. Lightning affects the quality of the radar data in varying degree at each range gate (the intense vertical spikes shown in the lower panels), and the combination of data from the two instruments allow for the separation of lightning (treated as noise) from the radar signal in order to reliably extract the vertical winds. By comparing the electric field variation with the disdrometer data, Petitdidier and Ulbrich also found that inversions in the field sometimes occurred, which were more directly associated with precipitation. At the end of a storm, the classical behavior in electrical activity was often observed, which was high positive field strength and negative cloudto-ground lightning, but with no rain. Most of the storms they were able to observe in Puerto Rico exhibited properties that were more characteristic of mid-latitude convection rather than storms found over tropical oceans. Thunderstorm research continues at Arecibo as a small but important effort to learn more about the finer structure of

Thunderstorm and Related Research at Arecibo Craig Tepley r. Monique Petitdidier, of CETP/ CNRS in VÈlizy, France, was kind enough to send me some viewgraphs and other material on the tropical convective thunderstorm research in which she and Dr. Carl Ulbrich of Clemson University were recently involved. Although we did not have a chance to present their mate-

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Electric Field and Rain-fall Rate measured on 1999/09/30
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ferent technique to infer droplet fall speed from radar reflectivity at a single frequency indicates that the latter approach to the problem is not very reliable. In addition to using the UHF system as a stand alone radar, we can also use its transmitter as a source and receive (biaxially) with a separate set of antennas configured as an interferometer [Palmer et al., Radio Sci., 32, p.749, 1997]. Using "Spatial Domain Interferometry" techniques, this instrument can potentially measure the three-dimensional structure of the wind field of the lower atmosphere, but it has only seen limited usage since it was established in 1995.

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Besides the radar systems at UHF and VHF, we once had a Time (s) capability to measure turbulent layers in the stratosphere using our S-band (2380 MHz) radar in Fig. 4: Electric field, rate of rain-fall, and backscattered signal from the Arecibo VHF radar measured for a bi-static configuration [see for several hours during the afternoon of 9 Sept. 1998. The top panel shows the changes in the field strength and direction (heavy solid line) and rain-fall rate (light solid line) observed during an active thunderstorm. The example, Woodman, Radio Sci., bottom two panels zoom in on the E-field (upper curve on each plot) and VHF radar data (lower curve on each 15, p.417, 1980 and the more plot) for two range gates from 15:03 to 15:11 AST. The radar signal was averaged over 128 records. Note the recent paper by Cho et al., Geogradual buildup in the field strength and the rapid discharges due to lightning, which is also a source of conphys. Res. Lett., 23 , p.1909, tamination to the VHF data. Aside from their science content, other information obtained from these different 1996 where he used a similar instruments can be combined to flag the lightning generated noise to better determine the winds from the radar approach using the NASA/JPL data. (Courtesy Monique Petitdidier) Goldstone radar]. Although our bi-static 2380 MHz system is currently unavailable, this capathese events. However, conventional an advantage in studies of the fall speeds bility could be re-established given sufmeteorologists often require extended, of water droplets to determine unambig- ficient research interest and financial long-term data sets in their research -- uously both the air speed of the back- resources. a difficult feat for Arecibo due to the ground wind and the droplet motion Radars, of course, are ideal instrumulti-disciplined nature by which we [Chilson et al., J. Atmos. Ocean. Tech., ments for storm observations due to their operate. Nonetheless, Arecibo does of- 10, p.663, 1993]. The VHF radar is only continuous remote sensing capability fer some unique features with its clus- sensitive to the motions of the clear air and ability to see through thick clouds. tered instrumentation, not found while the UHF radar is primarily sensi- However, we also have developed an elsewhere, but which are important tools tive to water droplets. After measuring excellent complement of optical instruthat can be used to study complex mete- the backscattered spectra at each fre- mentation at Arecibo. Although not yet orological phenomena. For example, the quency, differences in their Doppler exploited to its fullest extent for meteobeams of our UHF (430 MHz) and VHF shifts would yield the true droplet fall rological research, our lidar facilities (47 MHz) radar systems are co-axially speed, while droplet size distribution and have recently undergone a face-lift aligned enabling simultaneous observa- number density can be extracted from the thanks to the generous support we retions at two frequencies within the same spectral shape and backscattered power. ceived through a NASA EPSCoR provolume of space. This has proven to be A comparison of this method with a dif- gram via our cooperation with the
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Conjugate Time (cycles/minute)

University of Puerto Rico. The funding enabled various wavelength extensions of our tunable-lidar systems, which will allow us to explore the distribution of minor species in the atmosphere, such as ozone and water vapor, using absorption spectroscopy. Our latest EPSCoR support also enabled a small augmentation to the scientific staff by creating a postdoctoral research associate position for which we are currently seeking suitable candidates (see p. 19). In the next year we plan to develop an ability to observe minor species of the stratosphere and troposphere via lidar remote sensing and encourage interested users to help us exploit these new and current capabilities for meteorological research. We have several projects in mind for thesis research that would apply our radars and lidars to study such things as the exchange properties between the stratosphere and troposphere, and these projects only await a few clever students to work on them. Look to our web site for a list of possible projects, or simply contact us to discuss your own ideas.

Tuesday, January 25, 20:29:57 2000

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Fig. 5: A spectral analysis of the frequency and time variations of the flux density from the pulsar PSR B0834+06. This secondary spectrum (see text) is displayed with a logarithmic gray-scale. The wisplike features extending from the origin have been seen before in other observations, but never with this sharpness, signal-to-noise ratio, or extent from the origin. Although Stinebring et al. believe the wisps are produced by scattering in the interstellar medium, their exact origin is currently unknown. The central vertical stripe is due to the sidelobe structure of the Fourier transform and should be ignored. (Courtesy Dan Stinebring)

Radio Astronomy Highlights Chris Salter and Mike Davis Pulsar Scintillation Observations an Stinebring, Kate Becker, JoaquÌn Espinoza Goodman and Clait Smith (Oberlin) and Maura McLaughlin and Jim Cordes (Cornell) observed a total of 11 pulsars in Jan. 2000 using the Arecibo Observatory Fourier Transform Machine (AOFTM). Most of the observations were at 430 MHz, with some at 1400 MHz. The AOFTM was used mainly in its 1024channel (10-MHz bandwidth) mode. Although a fair bit of radar interference was present, it did not cause serious defects in the dynamic spectra, perhaps because of its spread-spectrum character and the relative immunity to interference of the AOFTM. This project is investigating pulsar scintillation, short-

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and long-term intensity variations in the pulsar signal caused by diffraction and refraction in the interstellar medium (ISM). By studying the effects on pulsar signals, much can be learned about the structure of ionized material in the ISM. The new observations extend those of Jan. 1999, reported in NAIC/AO Newsletter 27. As discussed there, a standard way to view the data is via a "dynamic spectrum" -- a grey scale showing intensity as a function of time and frequency. This allows the measurement of correlation time-scales and bandwidths which can be compared with model ISM predictions. For studying pulsar scintillation, the Arecibo telescope and the AOFTM provide a unique combination of high signal-to-noise and time and frequency resolution. In addition to producing dynamic spectra from the new observations, exciting results are emerging from the lat-

est run in the form of "secondary spectra" -- the two-dimensional power spectra of the dynamic spectra. Secondary spectra allow deep searches for coherent patterns in the dynamic spectra which show up as well-defined features in the Fourier domain. As an example, Fig. 5 shows a secondary spectrum for PSR B0834+06. Similar results are found for three other pulsars, B0823+26, B0919+06 and B1133+16. On first inspection, the main result is the presence of wisp-like features extending from the origin. Tantalizing hints of these wisps were seen in the 1999 observations for B1133+16. What makes these features different to what has been reported before is their sharpness in the secondary spectrum plane. This is due primarily to the increased frequency and time resolution of the new observations when compared with previous measurements. Of course, it also requires that the un-

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derlying phenomenon be "high-Q" in this representation. Several striking features are seen in the new data. Firstly, in all four pulsars the wisps show roughly bilateral symmetry about the vertical axis. Secondly, the wisps curve significantly and in a consistent sense -- away from the vertical axis. The wisps are strong features relative to the noise floors in the secondary spectra. That they are not seen for all the pulsars studied, but consistently for the above examples, strongly points to their being real signals in the data, and extraterrestrial in origin. Furthermore, inspection of previously published data with different telescopes shows similar features at a lower signal-to-noise ratio. Given that the wisps are not an artifact of equipment or processing, what are they? Stinebring et al. are currently exploring this important question. The character of the wisps in these observations, coupled with a comparison with previous "criss-cross" patterns in published dynamic spectra, are suggestive of a quiescent state of a more general ISM phenomenon. The wisps are so regular this time (bilateral symmetry, similarly curved) that it looks as if whatever is producing them is a very basic component of the scattering material that may well be related to peculiarities of the inhomogeneity spectrum, rather than discrete spatial structures in the scattering material. PSR 1907+0918 and SGR 1900+14 Kiriaki Xilouris (UVA) and Duncan Lorimer (NAIC) have recently obtained a phase-coherent timing solution for PSR J1907+0918 -- the 226-ms pulsar that they found near the soft gamma-ray repeater, SGR 1900+14 (see NAIC/AO Newsletter 26; Nov 1998). Timing measurements now span well over a year and yield an accurate position for the source, as well as a highly significant measurement of the spin-down rate. These parameters show that the pulsar is located only two arc-minutes away from the magnetar, SGR 1900+14, with a characteristic age inferred from the spinMarch 2000, Number 29

down rate of only 38,000 yr, very close to the limit reported in NAIC/AO Newsletter 26 from preliminary measurements. Thus, rather than being a rather "boring" pulsar with an age of a few million years, PSR J1907+0918 is comparable in age to the magnetar, which is thought to be ~10,000 yr old. Of course, finding a pulsar projected so close to the magnetar does not mean that they are related in any way. Based on the sensitivity estimates of the search, and the pulsar number density along this part of the Galactic plane, a pulsar is expected to be found in every 80 pointings. The simplest explanation then is that this is a pulsar that just happens to lie along a similar line of sight to the magnetar. What is remarkable about J1907+0918 is that it is so young. Its characteristic age puts it in the "top 20" youngest radio pulsars. Furthermore, (see NAIC/AO Newsletter 26), it possesses a flat spectrum typical of other young pulsars. Given that supernova remnants are visible for up to 100,000 yr, it is natural to ask where the remnant of the explosion that produced this young neutron star is? Xilouris and Lorimer speculate that the supernova remnant associated with this pulsar is G48.2+0.6, thought by many to be associated with the magnetar. Presently, there is no clear case for preferring one neutron star over the other as a candidate. An acid test of an association would be a measurement of the proper motion direction of either neutron star across the sky as it moves away from the site of the explosion. Future VLBI proper motion measurements for PSR J1907+0918, perhaps using an array of Arecibo, Effelsberg and the GBT, would provide an important clue towards solving this mystery. Pulsar Instrumentation The Arecibo-Berkeley Pulsar Processor (ABPP) is a 32-channel signal averager that performs coherent dispersion removal in the time domain. The maximum total bandwidth is 112 MHz unless full Stokes parameters are desired, when it is 28 MHz. The usable bandwidth is

set by dispersion at each radio frequency. The user interface runs from the observer workstation, and remote operation is possible once one is familiar with the system. Real-time display of pulse profiles and calibration information is available. Copies of the ABPP are installed at Effelsberg and Green Bank. Information is available at: http://www.naic.edu/ ~abpp. Interested observers are encouraged to contact Don Backer (Berkeley) (dbacker@astron.berkeley.edu) for further details BACSPIN, the Berkeley-AreciboCaltech Swift Pulsar INstrument, is a 96channel data acquisition system modeled on the Penn State Pulsar Machine (PSPM). The maximum total bandwidth is 182 MHz. Total power "search" data can be acquired on a disk array or on DLT tapes at rates of up to 15 MB/s. A signal averaging mode is available for timing and other studies. This mode has been used for the past year on the original processor at NanÃay. Backer and his grad student Andrea Somer (Berkeley) are developing operational procedures to use BACSPIN to sample the 1-2 GHz bands of Arecibo's high-frequency receivers. Observers should contact them about using this system. HI in the Galaxy HI profiles of 21-cm emission often exhibit self-absorption in the directions of nearby dark clouds in the Galaxy. This has long been recognized as a possible probe to the atomic hydrogen component in these clouds otherwise dominated by molecular species. However, due to limited angular and frequency resolution and relatively limited knowledge of dark clouds available in past studies, the origin of HI self-absorption and the physical conditions of the gas responsible for it are not firmly established. The Arecibo Gregorian system offers both broad-band frequency coverage and high sensitivity. Arecibo also has respectable angular resolution for this problem. For example, the 3-arcmin beam size of the telescope at L-band corresponds to about

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6000 5000 4000 3000 2000 1000 4000 3500 3000 -20 -10 0 10 20

6000 5000 4000 3000 2000 1000 -10 0 10 20 30

is higher than the canonical value of 3â10-17 s-1 cm-3, which is well confined by thermal balance considerations. Thus, it is difficult to raise this value very far, or the increased heating would raise the temperature of dark clouds considerably above observed values. (2) H2 formation on dust grains is much less efficient than previously accepted. The second possibility appears plausible, but this conclusion remains tentative at the present time. HI in High Velocity Clouds (HVCs) There is a growing consensus that galaxy formation is a continuing hierarchical process: a large number of rather low-mass condensations are envisioned as merging into larger structures. Recently Blitz et al. (1999, ApJ 514, 818) revived the suggestion that HVCs are scattered throughout the Local Group, and argued that they are the primordial building blocks fueling galactic growth and evolution. The large HVC complexes, which dominate the total HI flux at anomalous velocities, would represent the phenomenon in close proximity, being about to be accreted into the Milky Way, or already undergoing such accretion; in either case, they would have been exposed to the Galactic radiation field and to strong gravitational torques. Thus, it is unlikely that the HVCs as usually cataloged (see Wakker & van Woerden 1991, A&A 250, 509) represent the phenomenon at a single evolutionary stage, or under comparable physical circumstances. The sample of 65 compact, isolated, HVC objects compiled by Braun & Burton (1999, A&A 341, 437) represents a more coherent population than would a sample including any of the major HVC complexes. The spatial and kinematic distribution of these CHVCs is consistent with their being a dynamically cold ensemble spread throughout the Local Group, with a net negative velocity with respect to the mean of the Local Group galaxies implying infall towards the barycenter with some 100 km s-1. Thus it seems that these objects are low-mass gaseous sub-dwarfs in the Local Group

6000 5000 4000

2500 2000 1500 1000 -10 0 10 20 30 3000 2000 1000 -10 0 10 20 30

Fig. 6: Superposed HI (filled) and 1667-MHz OH (unfilled) spectra for 4 molecular clouds. All the OH spectra have been multiplied by a factor of 30. The HI Spectra for TMC1 and L1495 have been offset by 2000 mJy. Note the essential coincidence of HI self-absorption and OH emission features in each case. However, it is not clear that the feature at -15 km s-1 in CB45 is associated with cold, molecular material. (Courtesy Di Li and Paul Goldsmith)

0.13 pc at the 140-pc distance of the Taurus Molecular Cloud (TMC1). Di Li (Cornell) and Paul Goldsmith (NAIC/Cornell) have observed 10 nearby dark clouds simultaneously at 1420, 1665 and 1667 MHz. The resulting HI line profiles show clear detection of selfabsorption in 6 of these. The absorption features in the other 4 are inconclusive due to their location on the steep side of underlying HI emission from the Galactic disk. Some of the HI and OH profiles are shown in Fig. 6. The HI self-absorption detected is reasonably narrow, coincides in velocity with OH emission lines and, most importantly, has an absorption temperature minimum of approximately 10 K. All three features are consistent with the picture that HI self-absorption is associated with the atomic hydrogen within the volume of
March 2000, Number 29

dark clouds, rather than, for example, being caused by an atomic halo or by foreground material. The low value of the minimum temperature is perfectly consistent with the temperature expected deep in well-shielded regions heated only by cosmic rays and cooled by molecular radiation. Li and Goldsmith have determined the abundance ratio [HI]/[H 2] to be 10 -4­10-3 in the dark clouds such as TMC1 and CB45. This is one to two orders of magnitudes higher than the expected values based on cosmic ray ionization. In all the regions in their study, the high extinction and lack of dominant embedded stars preclude any significant role being played by photon ionization. This leads to two possible explanations for the high HI abundance; (1) The cosmic ray rate in the dark clouds

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potential, but typically at large distances (600 kpc) from the Milky Way or M31, with linear sizes of order 10 kpc and gas masses, MHI, of about 107 M , corresponding to those of (sub-)dwarf galaxies. Robert Braun (NFRA) and Butler Burton (Leiden) have begun a program of high resolution imaging of the CHVCs to study their kinematics and physical conditions. Imaging of 6 sources with the Westerbork array (Braun & Burton 2000, astro-ph/9912417) revealed a characteristic source morphology of 1­10 compact cores (each of 1­10 arcmin diameter) distributed over a 30arcmin region and embedded in a diffuse halo (~1 degree FWHM in extent). Several of the compact cores are sufficiently optically thick that good estimates of both column and volume densities could be made, allowing crude distance determinations from D=N HI/(n HI )=700 ± 300 kpc. Many cores also display a velocity gradient along the long axis of an elliptical distribution consistent with circular rotation (with Vrot~15 km s-1) in a flattened disk system. At a distance of 700 kpc, very high dark-to-gas mass ratios of 30-50 are indicated, scaling as D-1. The compact cores typically account for 40% of the HI line flux while covering some 15% of the source area. The narrow line width of all core components (2-10 km s-1 FWHM) has allowed unambiguous identification of these with the cool condensed phase of HI, the CNM, with kinetic temperatures near 100 K, while the halos presumably represent a shielding column of warm diffuse HI, the WNM, with temperatures near 8000 K. However, since the diffuse halos could not be detected directly in the interferometric imaging this remained conjecture at that time. In Nov. 1999, Braun and Burton furthered their study of the CHVC population via Arecibo observations. Source positions and sizes had been derived from Dwingeloo 25-m telescope data at only 36-arcmin resolution, so the first shift at the telescope was used to obtain

fully sampled HI images of a 1 â 1 square degree field centered on each accessible source. Thanks to substantial real-time assistance from the Arecibo staff, and Phil Perillat in particular, first pass images of integrated HI for each field were produced shortly after ending each observing sequence. From these, a target position was chosen and re-observed with a series of 2-degree long drift scans. The drift scans were repeated for the remainder of the run to get the highest possible sensitivity along one cross-section

through each source. In the best cases, some 60 drift-scans were accumulated per source, giving integration times of 14 min per beam. Measured rms sensitivities expressed in HI column density (NHI) were as good as 7â1016 cm-2 over 10 km s-1. Figs. 7 and 8 show some results of the Arecibo imaging. The upper two panels display the integrated HI and velocity field over a 1 square degree field for CHVC 186-31-206 and CHVC 15839-285. Both show a prominent velociA186-31-206 -210 -205

A186-31-206 0 5

10

15

20

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DECLINATION (J2000)

DECLINATION (J2000)

07 00 06 50 40 30 20 10 04 16 00 15 00 14 00 13 00 RIGHT ASCENSION (J2000) Contours: 5, 10, 20, 35, 50

07 00 06 50 40 30 20 10 04 16 00 15 00 14 00 13 00 RIGHT ASCENSION (J2000) Contours: -210, -207, -204, -198, -195
-196

Vel (km/s) FWHM (km/s) Log(NH)

-198 -200 -202 -204 -206

A186-31-206 0 50 04 18
RIGHT ASCENSION (J2000)

Dec= +06:36:19 100 150

17 16 15 14 13 12

-208

50 45 40 35 30 25 20 15

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11
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Contours: -20, 20, 50, 100, 200 500, 1000 mK

18.0

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RA (J2000)

Fig. 7: Top left: Arecibo image of CHVC 186-31-206 showing NHI at 3.5-arcmin resolution; contours are drawn at levels of 5, 10, 20, 35 and 50â1018cm-2. Top right: Intensity-weighted line-of-sight velocity, with contours of vLSR drawn at the indicated velocities. Bottom left: Position, velocity cut at a fixed declination of +06:36:19. Contours are in units of brightness temperature. Bottom right: Variation of line-of-sight velocity, velocity FWHM and NHI with position. (Courtesy Robert Braun and Butler Burton)

March 2000, Number 29

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CHVC158-39-285 0 5 10

15

20

CHVC158-39-285 -290 -280 -270

-260

DECLINATION (J2000)

DECLINATION (J2000)

16 30 20 10 00 15 50 40 02 43 00 42 00 41 00 40 00 RIGHT ASCENSION (J2000) Contours: 5, 10, 20, 30

16 30 20 10 00 15 50 40 02 43 00 42 00 41 00 40 00 RIGHT ASCENSION (J2000) Contours: -295, -292, -289, -280, -275, -270, -265, -265

-270 -275 -280 -285 -290

CHVC158-39-285 Dec= +16:17:30 0 50 100 150
RIGHT ASCENSION (J2000)

02 45 44 43 42 41 40 39 38
Log(NH) FWHM (km/s)
-295

50 45 40 35 30 25 20 15

20.0

19.5

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-260 -300 -340 VEL_LSR in km/s

VCs, which has allowed high resolution (3.5 arcmin) detection of the diffuse CHVC halos for the first time. (1) All measured HI linewidths of the halos are between ~ 25 and 30 km s-1 FWHM, just in excess of the 24 km s-1 FWHM thermal linewidth of 104 K gas, confirming that these structures are the expected warm neutral medium cocoons required for both shielding and pressure confinement of the condensed CNM cores. (2) While the CNM cores show ordered velocity gradients suggestive of circular rotation in a flattened disk system, the WNM halos do not share the same velocity gradients, but are concentrated near the systemic velocity of each source. A more nearly spherical distribution for the WNM halos may be indicated, which may not be too surprising since the thermal velocity dispersion of 10 km s-1 is not much less than the apparent rotation velocity of most cores. The halo gas is likely to be only loosely bound to each object. The Arecibo imaging also shows that several CHVCs are more sharply bounded on one side of the position, velocity cut than the other; it is hoped to address this tendency in new Arecibo observations. Also investigating HVCs, Jonathan Smoker, Nicolas Lehner, Francis Keenan (Belfast) and collaborators have used their Arecibo observations of the 21-

Vel (km/s)

18.5

18.0

Contours: -10, 10, 20, 50, 100,

17.5

02

45

44

43

42

41

40

39

38

RA (J2000)

DECLINATION (J2000)

Fig. 8: Top left: Arecibo image of CHVC 158-39-285 showing NHI at 3.5-arcmin resolution; contours are drawn at levels of 5, 10, 20, 30â1018cm-2. Top right: Intensity-weighted line-of-sight velocity, with contours of vLSR drawn at the indicated velocities. Bottom left: Position, velocity cut at a fixed declination of +16:17:30. Contours are in units of brightness temperature. Bottom right: Variation of line-of-sight velocity, velocity FWHM and NHI with position. (Courtesy Robert Braun and Butler Burton)

M15 HVC HI column density map, Arecibo 12 30 25 20 15 10 05 00 11 55 21 31 00 30 30 00 29 30 00 RIGHT ASCENSION (J2000)

80

60

ty gradient aligned with the major axis of the brightest core component, suggesting circular rotation in a flattened disk system. The short integration time per beam in these maps only allows NHI > 5â1018 cm-2 to be detected, and only the brightest portions of the surrounding halos can be seen. In the lower panels deep cross-cuts (at the indicated declination) of 2-degree length are shown. Faint halo emission is detected in these deep integrations out to substantial distances, as shown in the NHI profile in the
March 2000, Number 29

lower right panel of each figure. The cool cores are embedded in diffuse halos with approximately exponential NHI profiles, extending from ~1019 cm-2 to at least 3â1017 cm-2. Although this is close to their current detection limit (over the ~80 km s-1 integration range), it is clear that longer cross-cuts will be required to determine where the actual edges of the neutral halos occur. Several important conclusions follow from this deep Arecibo imaging of CH-

40

20

0

Fig. 9: Arecibo HI column density map towards the M15 HVC, integrated between 40VLSR 90 km s-1. The greyscale is shown in units of 1018 cm-2, with contours at NHI=1018â(20, 30, 40, 50, 60, 70) cm-2. (Courtesy Jonathan Smoker)

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cm HI line to map a region of 0.675 â 0.625 square degrees in the HVC centered upon the globular cluster, M15 (Fig. 9). The HVC gas is found to be clumpy, with a peak surface density of 8â1019 cm-2. They also made a long HI integration towards HD203664, a halo star some 3.1 degres from M15, for which optical HVC absorption has been previously detected. No HI with a velocity > 60 km s-1 was found above a brightness temperature limit of 0.5 K. Additional pointings did detect HVC gas about mid-way between HD 203664 and M15. They also obtained Arecibo HI spectra and low resolution optical CaII H and K line spectra towards 15 field stars towards M15 in an attempt to obtain the distance to the HVC. High velocity HI is detected for 7 of these lines of sight. The spectral types for 12 of the stars were determined and, assuming them to lie on the main sequence, their distances estimated to be in the range 150-1350 pc. Non-detection of HVC Ca II absorption in these stars, combined with a previously derived distance for HD 203664 of 3.2 kpc, tentatively implies that the HVC lies in the distance range 1350 0.3 contain a large population of blue galaxies, many of which have spectra strongly suggestive of current or recently concluded star formation. Morphological studies carried out with WFPC2 on the Hubble Space Telescope (HST) have shown that a larger fraction of distant-cluster galaxies are classified as spiral, irregular, or interactions/mergers than in nearby clusters. The eventual fate of these galaxies -- their evolved counterparts at low z -- is

now a key unsolved problem of cluster galaxy evolution. It has often been proposed that ram pressure stripping from the hot intracluster medium can rapidly remove gas from rich cluster galaxies, or that tidally induced perturbations can funnel gas to the galaxy centers, where star formation depletes the supply.

NGC7648 0.029

0.028

0.027

Flux (Jy)

0.026

NGC7617 0.0005

Recently, Nelson Caldwell (SAO), Alejandro Gaba, Jim Rose, and K risti Dendy (N. 0 Carolina) have studied nearby rich clusters, revealing the presence of -0.0005 on-going or recentlyended star formation in 2000 3000 4000 5000 6000 early-type galaxies in Velocity (km/s) several rich clusters, such as Coma (Caldwell et al. 1993, AJ, 106, 473; Fig 10: Continuum-subtracted 21 cm profiles of (a) NGC7648 and Caldwell & Rose 1997, (b) NGC7617. Flux in Jy is plotted versus velocity in km/sec. (Courtesy Jim Rose) AJ, 113, 492; 1998, AJ, 115, 1423). These findings are primarily based on multi-fiber optical spectroscopy. Furthermore, the starbursts in cluster mem- profile indicate that the gas is settled into bers seem often linked to substructures a rotating disk, or do unusual kinematmerging with the main cluster (Caldwell ics prevail? Initial service observations & Rose 1997). Given that the star-form- were obtained of 4 galaxies in the Peing galaxies in nearby clusters appear to gasus I cluster, which lacks a hot intracbe the counterparts of those seen at high- luster medium and has a low velocity er z, the proximity of clusters such as dispersion. Hence any unusual star forComa provides an excellent opportuni- mation is likely to result from external ty to reveal the mechanism(s) triggering gravitational perturbations. The Arecibo the star formation activity, and thus to observations were of 4 galaxies with earbetter understand the Butcher-Oemler ef- ly-type morphologies, but for which Vigroux et al. (1989, AJ, 98, 2044) found fect. that one, NGC7648, has on-going highGaba, Rose and Dendy have begun level star formation, while the other 3 an Arecibo program to investigate the HI have spectroscopic evidence for recentcontent of star-forming and post star- ly terminated star formation. Improved forming galaxies in nearby clusters. optical images reveal that NGC7648 has They wish to determine whether post complex inner morphology indicative of star-forming galaxies still maintain a re- a merger, while NGC7617 has a large sidual supply of HI, or whether they have dust lane a few kpc outside the nucleus. been entirely cleaned of their gas reser- The Arecibo spectra of these two galaxvoir. Also, if detected, does the 21-cm ies (Fig. 10) show that HI is still present

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4â10-3 2â10
-3

0000+336 Sy2

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0 6500 7000 7500 8000

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Heliocentric Velocity (km/s)
Fig. 11: An example set of recently obtained HI-spectra from Seyfert-I and Seyfert-II galaxies. (Courtesy Tapasi Ghosh)

in both, at a level of 5â108 and 2â108 M in NGC7648 and 7617 respectively. These high levels of HI for early-type galaxies indicate that a residual supply of HI gas remains after the termination of star formation, while in NGC7611 and 7557, HI is not detected. In addition, the HI profile for NGC7648 indicates that the remaining gas has not yet settled into a well-defined disk, as opposed to the post star-forming NGC7617, where a double-horned HI profile appears to be present. Further observations will be made in June of star-forming and post star-formation galaxies in the Coma and Virgo clusters. Recent Arecibo HI observations of low surface brightness (LSB) galaxies in the z < 0.1 universe have allowed a new determination of the true (selection effect corrected) galaxy population to a central surface brightness of 25.0 B
March 2000, Number 29

mag arcsec-2. Taking advantage of having a catalog in which each galaxy has a known central surface brightness, scale length, and redshift, Karen O'Neil (NAIC) and Greg Bothun (Oregon) applied a bi-variate volume correction to their data and extended the surface brightness distribution function by one magnitude, to 25.0 B mag arcsec-2. The result is a flat (slope = 0) surface brightness distribution function from the Freeman value of 21.65±0.30 to the survey limit of 25.0 mag arcsec-2, more than 10 away, showing the number density of galaxies in the local universe to be dominated by LSB systems. Additionally, as these systems typically are intrinsically large and luminous, O'Neil and Bothun have been able to show that LSB galaxies may contribute 9 ­ 20 times more baryons to the local universe than their high surface brightness coun-

terparts, and that a significant percentage of the baryonic content of the Universe is likely contained in potentials only dimly lit by the embedded galaxy. Dargan Frierson (N. Carolina State), JoAnn Eder, Tapasi Ghosh and Chris Salter (NAIC) have made an unbiased survey of HI in Seyfert galaxies to test theories designed to unify the Seyfert-1 (broad-emission line) and Seyfert-2 (narrow-line) classes of active galaxies. These theories, which explain apparent differences between the two subclasses as due to orientation effects, can be examined by comparing various HI properties derived from 21-cm spectra. If unification theory is correct and the accretion disks of Sy-1's are face-on, while those of Sy-2's are edge-on, and if the galaxy HI disk is aligned with the accretion disk, then Sy-1 HI spectra should have the narrower velocity widths, while
NAIC/AO N ewsletter

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RU Ser (15540+0910)
600 400 1612 MHz

200 0 80 1667 MHz

40

0 10 20 30 40

Local standard of rest velocity (km/s)

Fig. 12: OH-line spectra of RU Ser (15540+0910) for the 1612and 1667-MHz lines. (Courtesy Murray Lewis)

sized by Murray Lewis (NAIC) with a new 1612MHz detection from RU Ser (15540+0910; Fig. 12), which lies just outside the above color range. The 1612-MHz spectrum is extremely unusual in having its strongest (or indeed any discrete) feature at the stellar velocity. In addition, it has normal features at the two velocity extremes, though its 1667-MHz spectrum only has a central peak. This morphology is almost unprecedented and is not exhibited by any other Arecibo OH/IR star. It also poses a challenge to accepted models for 1612MHz masers.

lower-density, pulsation-driven wind, so tangential gain-path masers at the stellar velocity in this inner, low-velocity wind can be simultaneously supported. However, this is inherently a short-term situation. As time elapses, the outer dust shroud will disperse and become ever less effective at protecting molecules, whereupon all of the 1612-MHz masers will disappear, as pulsation-driven massloss does not on its own provide enough dust protection for 1612-MHz masers to flourish. RU Ser is thus the 1612-MHz equivalent of the rare, double-shelled CO sources found about some carbon stars. The OH megamaser (OHM) survey by Jeremy Darling and Riccardo Giovanelli (Cornell) is now more than halfway complete. OHM candidates were selected from the PSCz redshift survey (Saunders et al 2000, MNRAS, submitted, astro-ph/0001117) and have z > 0.1, with an IRAS detection at 60 µm. These criteria select luminous and ultraluminous infrared galaxies. Thus far 32 new OHMs have been identified. It is expected that the full survey will produce 5060 discoveries in total, including a few OH gigamasers (LOH > 104 L ). The completed survey will double the overall sample of OHMs, and increase the z > 0.1 sample by a factor of seven. One gigamaser has been detected at z=0.217 spanning more than 1000 km s-1 in the rest-frame (Fig. 13).

total derived HI masses and surface densities should be comparable for the two classes, HI emission being orientationindependent. During the summer of 1999, the Arecibo telescope was used to observe a sample of 61 Seyfert galaxies with redshifts < 0.044 which were previously unobserved or undetected at 21cm. HI was detected in 39 galaxies (64%), of which 20 are Sy-1 and 19 Sy2. Typical spectra are shown in Fig. 11. The distributions of HI mass and surface density were found to be similar for the two classes, consistent with orientation independence. However, the distributions of the velocity widths were not significantly different either, which could indicate random alignment of the HI and accretion disks. Further, the ratio of the continuum flux density (orientation-dependent for core and jet emission) and the HI mass (orientation-independent) might be expected to display significant differences between the two classes. Preliminary results using NVSS continuum flux densities do not appear to show this. Molecular-Line Studies Existing Arecibo surveys of color-selected IRAS sources are complete within a broad, yet still restricted, color range. In Aug. 1999, this restriction was emphaMarch 2000, Number 29

Intensity (arbitrary scale)

Lewis has found that his transient shell model for high-latitude OH/IR stars (ftp://ftp.naic.edu /pub/publications/bml/ ho2.ps.Z) suggests an explanation. In summary, this amounts to RU Ser being the exception that proves the rule about how 1612-MHz masers originate. Let us suppose that RU Ser has just completed a normal transient superwind episode, which provided dust protection for its OH molecules that enabled it to exhibit a usual complement of 1612-MHz masers. Then for a time immediately after the superwind stops, while the star develops a pulsationdriven rather than F12032+1707 dust-driven massz=0.2170 loss mode, it still has enough dust protection in place to exhibit normal 1612-MHz masers with a velocity near the terminal expansion velocity of Heliocentric Velocity (km/s) gas in their prior emission zone. Fig. 13: The OH spectrum of IRAS F12032+1707. The abscissa and Hence those in RU redshift refer to the optical heliocentric velocity. The spectrum uses Ser. But this same the 1667.359-MHz line as the rest frequency for the velocity scale. dust will also protect The dotted line indicates the shape of the baseline subtracted from OH molecules in the the calibrated spectrum. (Courtesy Jeremy Darling) newly emer ging,

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Darling and Giovanelli have also observed significant variability in several OHMs over time scales of 2­9 months, including the gigamaser IRAS F12032+1707, see Fig. 13. This is the first documented detection of variability in OHMs, and suggests that the emission regions which show variability are quite small (< 0.5 pc), regardless of whether variability is intrinsic to the source or produced by interstellar scintillation. They suspect that much of the observed variability may be caused by interstellar scintillation because the observed modulation indices and timescales are consistent with refractive scintillation in the strong scattering regime at 1.5 GHz (Walker 1998, MNRAS, 294, 307). Variability studies of OHMs can place powerful constraints on the emission regions of OHMs, including the segregation of different spectral components into different physical scales. A detailed study of variability in OHMs can provide new insight into the physical emission mechanisms of OHMs (e.g. differentiate between masers which are saturated or unsaturated, extended or compact, and powered by AGN or starbursts).

Coordination Agreement with 140 ADS, PRANG -- Redshifted HI/OH work remains viable at Arecibo Tapasi Ghosh

F

ollowing almost a year of meetings, discussions and coordinated tests, Arecibo Observatory and the 140th Air Defense Squadron of the Puerto Rican Air National Guard (140 ADS/PRANG) have come to an agreement by which Arecibo observations in the lower Lband (between 1200 - 1400 MHz) will still be possible. Why was this necessary at all? Just as the upgrade was finishing, and a section of our users community was looking forward to using the new broadband receivers and correlator to study far-off neutral hydrogen and OH molecules, we found that the lower part of the L-band had become extremely busy in the interim. In fact, in mid 1998, while we were still planning a programmable radar blanker to permit use of the OFFpulse time of the handful of military radars then present (Fig. 14a), unbeknown to us a new frequency-hopping radar was being installed at 140 ADS/PRANG. This so-called AN/FPS-117 system can be programmed to randomly select any one of 20 dual-frequency channels lying within the frequency range 1225 ­ 1400 MHz (Fig. 14b).

Indeed, by US regulations this part of the spectrum is reserved for radio navigation and location purposes by mostly government agencies (non-Govt. use is allowed in some parts of this spectral range.) However, footnotes US-311 and RR-718 state that "administrations are advised to take all practicable steps to protect Radio Astronomy Observations down to 1330 MHz" in the vicinity of observatories listed in the rule-book. Within Puerto Rico, the Observatory has been utilizing the benefits of sector blanking of the TARS system at Lajas operating at 1241/1256 and 1249/1261 MHz (by virtue of a Memorandum of Understanding between the US Air Force and the NSF). However, with the arrival of the AN/FPS-117 system so close to the Observatory, it appeared as if all hopes of ever using this part of the spectrum had been lost. The most difficult part in this process for us was to find who it was that had caused our monitoring system to record spectra such as that shown in Fig. 14b. Here, the Puerto Rico Spectrum Users' Group meeting yet again proved its usefulness. During the October 1998 meeting, we presented the situation to the community and received an immediate answer. Both Mr. Mike Torres, DoD's Area Frequency Coordinator for Puerto Rico, and participants from another squadron of PRANG told us that the new

FAA San Juan Airport radar
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Fig. 14: Fig. 14a (left) shows the military radars that operate in the lower L-band between 1200 and 1440 MHz. On the right, fig. 14b shows the 140 ADS/ PRANG frequency hopping radar over the same range. (Courtesy Tapasi Ghosh)

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Mode A

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stitututions. New among these projects is the AOVEF Learning Center. Construction documents for the new Learning Center, to be constructed adjacent to the Visitor Center, are being prepared by architect Luis Badillo, who designed the Visitor Center (see graphic). The new facility will include a stateof-the-art classroom that will host our teacher workshop programs, and other meetings associated with the Arecibo Observatory. This project is also being funded by FAR. We are pleased to have received a continuation grant from the FAR towards our second series of the "Angel Ramos Foundation Workshop for Distinguished Science Teachers". Last summer a total of 44 teachers from throughout the Island participated in the summer program. Our collaboration with the FAR began ten years ago when this organization became the principal donor of the Center that proudly bears their name. Thanks to their continuing support, our outreach and education programs are providing increasing opportunities for the enrichment of teachers, students, and the general public who continue to visit us. The Arecibo Observatory is an affiliate member of the Puerto Rico NASA Space Grant. The main goal of the Space

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Fig. 15: This graphic maps out the current agreement for use of the lower L-band by 140 ADS/PRANG. During coordinated times their radar will operate in one of these modes, to be specified by the Observatory. (Courtesy Tapasi Ghosh)

radar at 140 ADS/PRANG at Punta Salinas might be the source. Within the next two months, Mr. Torres arranged for us to speak at a Joint Radar Planning meeting, where Mike Davis presented a wonderful case for Astronomy and the need for coordination. Once this contact had been made, the rest was smooth sailing. We found many friends at Punta Salinas - the commanding officer, LtCol. Humberto PabÑn himself, Chief Dow from the Pentagon, in charge of the AN/FPS117 installation, Maj. MalavÈ, SgtMaj. Maldonado and Sgt. FalcÑn to name but a few. After a number of discussions and joint test runs, we agreed on operational modes that would be mutually compatible. Consequently, a Letter of Agreement was signed to this ef fect on November 10th, 1999. According to this, during the times when the Arecibo Telescope is scheduled to operate within this band, AN/FPS 117 will operate in a twochannel mode. The specific set of frequencies will be recommended by the observatory from three possibilities, such that the planned observations will be as far from the AN/FPS117's channels as possible. However, during special situations, as well as for system checks, with advanced notice (and at any other times when AO is not scheduled to use that part of the spectrum), AN/FPS-117 may use all of its allocated frequency channels. In the associated cartoon (Fig. 15), the current arrangement is explained. We have also added a special RFI-related section to our Proposal Cover Sheet where a user can request such coordination as is needed for the success of the proposed observation.

We thank all the authorities at 140 ADS/PRANG, and especially LtCol. PabÑn, for their understanding and willingness to share the spectrum so wisely, and also Mr. Mike Torres (DOD AFC, PR) for making all this possible. In the future, we still plan to develop the programmable radar-blanker, making the entire L-band covered by our wide-band Gregorian receiver accessible to our users.

News from the Angel Ramos Visitor Center JosÈ L. Alonso and Daniel R. Altschuler fter a year of work, the production of "A day in the Life of the Arecibo Observatory" is almost complete. Its premiere will be shown at the time of the third anniversary of the Angel Ramos Foundation Visitor Center. It will provide a behind the scenes tour of daily Observatory operations in a 20 minute documentary. The film, sponsored by the Angel Ramos Foundation, was produced by Trillion Productions, of Chicago. The Angel Ramos Foundation (FundaciÑn Angel Ramos; FAR) was founded in 1958 by the late Angel Ramos, a pioneer in communications in Puerto Rico and President of El Mundo Enterprises. He established the first Puerto Rican TV station (Telemundo) and published the important El Mundo newspaper. The FAR has benefited hundreds of deserving projects in Puerto Rico, contributing to charitable, educational, health-care, and cultural projects and in-

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Schematic of the Learning Center Annex to the AOVEF. (Courtesy JosÈ Alonso)

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Grant program is to enhance local research and education in aerospace related fields. As part of this affiliation we have received a grant to support the construction of a scale model of the Solar System to be placed along the entrance road to the Visitor Center A new partnership between the Arecibo Observatory and the NSF funded Collaborative For Excellence in Teacher Preparation (CETP) at the University of Puerto Rico will allow 20 students from their teacher preparation programs to participate in a summer workshop at the Observatory.
Victor Santiago (Photo by Tony Acevedo) JosÈ "Cheo" Rosa (Photo by Tony Acevedo)

Employee(s) of the year 2000 Daniel R. Altschuler his year the committee selecting the employee of the year, composed of Julio Crespo, Tony Crespo (employee of the year 1998), SofÌa Cuevas, Luis Heredia, and Carmen Segarra, had a very difficult job. Four of the candidates were outstanding and the committee was not able to recommend one winner. It was equally difficult for me to make a decision. All four candidates had already been nominated last year and all had more than 28 years of service. Since this was going to be the last award of the millenium (according to some), and therefore a special occasion, I decided that all four should be awarded with this recognition. So, on December 16, and in the presence of fellow employees and their families we had the award ceremony. It was an emotional affair and some people were moved to tears. Indeed, there was not a dry glass eye in the house. The employees of the year 1999: JosÈ ChacÑn, born in Barrio Esperanza, began work at the Observatory 28 years ago in 1972. He worked as a painter on the platform and later as a groundskeeper. He is currently the leader of the painter rigger brigade.

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Born in Barrio Esperanza and after graduating from the Arecibo vocational school, VÌctor Santiago came to the observatory 35 years ago in 1964! He has worked in the maintenance department ever since, and currently is supervisor of the construction group. He is the brother of BenjamÌn Santiago, who for many years worked with telescope operations. After studying in the RCA Institute in New York, JosÈ (Cheo) Rosa came to Arecibo from the Bronx 29 years ago. Together with his partner, Antonio Nol-

la, they have served our many generations of receivers very well. Antonio Nolla, a native of the famous town of Cataßo, the other half of the receiver dynamic duo, came to work after graduating from the Instituto TÈcnico de San Juan, in 1967. He keeps at it after 32 years of good service.

Antonio Nolla (Photo by Tony Acevedo)

JosÈ ChacÑn (Photo by Tony Acevedo)

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Computer Department News Arun Venkataraman he AO Internet link no longer feels like a rush-hour traffic jam ­ well, most of the time anyway, following the installation by the PR Telephone Company of a "T1" link to the Observatory with dedicated uplink bandwidth to the mainland. "FTP" transfer rates are typically 70-150 kbytes/s with high reliability, and remote access to observatory machines is reported to be quite painless. We are in the process of transferring services from the old 56kbps link to the new 1544kbps one. In parallel with the upgrade of the external network link, the internal shared-coaxial 10Mbps ethernet has been largely replaced by a a switched 100Mbps system with a 1000Mbps (gigabit) "backbone". All "downstairs" VSQs are now equipped with networked X-terminals. The data reduction software environment continues to be largely based on Sun Microsystems workstations running Solaris 2, with notable exceptions in the Optical and Lidar facilities. Planning is under way for adoption of the NRAO AIPS++ data reduction system. A recent development is the use of the freelyavailable Linux operating system for data acquisition using off-the-shelf PC hardware -- the Wideband Arecibo Pulsar Processor (Bill Sisk, Andy Dowd and Jeff Hagen) has been a successful test of this approach.

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With Jean-Luc Margot facing a onemonth deadline for building a machine to observe a passing asteroid from Spain, Jeff qúuickly adapted code from a Solaris-based pulsar machine (courtesy of Stuart Anderson at Caltech) to do the needful. A generic socket library written by Jeff has also found its place in the observatory, being put to good use as part of the Radio Astronomy user interface (see back page). At the time of writing, Jeff is back at the Observatory for two weeks to continue development of the WAPP -- thanks to NRAO, again. Donna Kubik Paul F. Goldsmith It is with a sense of sadness that I am writing that Donna Kubik is leaving NAIC. This is in part because of the loss for NAIC, but also in part because it is a consequence of a family illness that has necessitated her relocating to the Chicago area. Although an employee of NAIC for only a few years, Donna had made a real impact in her position as the Observing Support Scientist. Just as a broad new range of capabilities of the Gregorian system was becoming available, Donna stepped in to assist local and remote observers and ensure successful completion of their projects. She brought to this job an impressive enthusiasm for astronomy combined with engineering training. I met Donna when she was an operator at the Cornell synchrotron -- but having developed a passion for radio astronomy, was already interested in Arecibo. She joined the staff of NAIC, initially working at Maple Avenue laboratory, while completing her MS degree in electrical engineering. Her thesis on the noise properties of high electron mobility transistors helped set the stage for her work in the electronics department at Arecibo, where she worked on a a variety of projects. However, her knowledge of and enthusiasm for astronomy made the move into observer support a very natural and beneficial one for users of the Arecibo telescope. All of those who were struggling with learning the new system were grateful for Donna's un-

stinting help, and will certainly miss her presence at the observatory. I understand that Donna has an excellent job at Fermilab, and I am sure that this is a good opportunity, but we all hope she can continue to enjoy astronomy while assisting in research projects. Good luck and best wishes, Donna! New Newsletter co-editor Daniel Altschuler After serving as newsletter co-editor for 6 years and producing 16 editions of the NAIC/AO Newsletter, Tapasi Ghosh stepped down from that post following the October 1999 issue. I am pleased to welcome to that position Duncan Lorimer. Duncan is a pulsar astronomer who recently completed an NAIC post-doc and will stay at Arecibo as a Research Associate. Although we will greatly miss Tapasi's work, Duncan is an excellent substitute and a welcome addition to the newsletter team.

Job Announcement Postdoctoral Research Associate in Laser Remote Sensing he National Astronomy and Ionosphere Center (NAIC) has an opening for a Postdoctoral Research Associate in the Optical Remote Sensing Group of the Space and Atmospheric Sciences Department at the Arecibo Observatory, Puerto Rico. The Observatory is an NSF-funded National Center in space and atmospheric sciences, and radio / radar astronomy, accepting observing proposals from scientists worldwide. Observing equipment related to research activities in space and atmospheric sciences at the Observatory include an incoherent scatter radar on the 305 m antenna, two lidars, and airglow measuring equipment.

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Comings and Goings Jeff Hagen Arun Venkataraman RAO Tucson generously lent us the services of Jeff Hagen for nine months last year. Jeff found the time to sail, golf, dive, and write drivers for Linux among other things. Little did I expect, when I showed him the problem I was having installing Linux on a newfangled 450MHz PC, that the Wideband Arecibo Pulsar Processor (WAPP) would eventually result. Jeff does Solaris too!

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It is expected that the successful candidate will be resident in Puerto Rico and will assist in developing and carrying out

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a research program involving stratospheric-tropospheric exchange of aerosols and water vapor using the lidar and radar facilities. The candidate will also act as a liaison scientist in his or her area of expertise to occasionally assist visiting investigators as they conduct their own studies at Arecibo. The Arecibo Observatory is located in the karst hills of the beautiful Caribbean island of Puerto Rico. A stimulating research environment is provided by approximately 25 resident staff scientists, postdoctoral fellows and graduate students, 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. NAIC

and the Arecibo Observatory are operated by Cornell University under a cooperative agreement with the National Science Foundation. Applicants should have a Ph.D. in engineering, atmospheric sciences, applied physics, or a related field. Experience working with tunable lasers, interferometry, and related optics is highly desired, as is a familiarity with models of atmospheric transmission and minor species absorption. Depending upon funding continuity, the position would be for two years, with the possibility of an extension to three. The successful candidate will be an employee of Cornell University, and hence eligible for all relevant University benefits. Salary and benefits are competitive, attractive, and include a relocation allowance. Evaluation

of applications will begin 1 January 2000, although applications received later than this may be considered. Please send a complete resume of academic, professional and personal data, a description of your research interests, and names and contact information of at least three references, to: National Astronomy and Ionosphere Center; Cornell University; 504 Space Sciences Building; Ithaca, NY 148536801; Attn: J. Morrison (Lidar ORSB). EOE/AAE. For further information about the position, contact Dr. Craig Tepley, ctepley@naic.edu. For general information about Arecibo, see website http:/ /www.naic.edu.

Radio Astronomy User Interface
Duncan Lorimer Present and future radio astronomy users of the telescope are invited to try out AO-Control -- a graphical user interface to the vX-works datataking program. AO-Control was developed from an earlier interface (PSR-Control) that has been in regular use by pulsar observers, both on-site and for remote observing, since May 1999. The new program is more generic and currently supports both pulsar and spectral line observing modes. Anybody with access to one of the Solaris machines at the observatory can try out the "off-line" version of the program which runs a dummy version of the vX-works program. Remote testing is possible by logging into "remote.naic.edu" in a secure shell, i.e.

% ssh remote.naic.edu -l username
Once in, make sure that the DISPLAY environment variable is set correctly and that your machine can accept X-clients from remote.naic.edu then type:

% gui
to start the interface. Further information can be found at the local URL www.naic.edu/~dunc/aoui. All comments and suggestions concerning AO-Control are most welcome. Please send e-mail to Duncan Lorimer (dunc@naic.edu).

Guidelines for Newsletter Contributors
The Editors The NAIC Arecibo Observatory Newsletter encourages and publishes contributed articles that are of general interest to Observatory users. In the past we had no set rules for these contributions. We have decided, for the sake of keeping the newsletter length manageable, to set up guidelines for contributed articles. These are the following: 1. We will accept no more than two contributed articles per newsletter. 2. The length of the text should not exceed one newsletter page. This is approximately 1000 words. 3. An article will be limited to two figures. We prefer them to be sent in PostScript® format.

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NAIC/AO Newsletter is published three times per year by the National Astronomy and Ionosphere Center. The NAIC is operated by Cornell University under a cooperative agreement with the National Science Foundation. Duncan Lorimer and Jonathan Friedman, Editors Address: NAIC/AO Newsletter HC03 Box 53995 Arecibo, PR 00612 Phone: +1-787-878-2612 Fax: +1-787-878-1861 E-mail: dunc@naic.edu or jonathan@naic.edu WWW: http://www.naic.edu

NAIC/Arecibo Observatory Newsletter 504 Space Science Building Cornell University Ithaca, NY 14853-6801 U.S.A.

*address correction requested

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