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Project Description:

HAAT -- the ``Humacao-Arecibo Astrometric Telescope'' -- is a radio
telescope planned to fill two separate, yet complementary, roles in a long-
term collaborative partnership between the UPR-Humacao and the Arecibo
Observatory. These are:


(1) To provide a unique research and teaching facility for the University
of Puerto Rico (Humacao Campus), allowing them to exploit the facilities of
the Arecibo Observatory of NAIC (an NSF-funded national center for
research.) In this guise HAAT would serve as an instrument with which
students and staff at UPR (Humacao) and other Puerto Rican universities can
develop skills in physics, astronomy, electronics, and computing. This
would apply from the classroom, through the teaching and research
laboratories, to use of the facilities of NAIC for full-scale research
projects. Puerto Ricans are significantly under-represented among the
nation's scientists and engineers, and the availability of a significant-
sized radio telescope, plus the collaboration of a leading national radio
astronomy center, to the University of Puerto Rico's (UPR) teaching and
research facilities would provide a remarkable opportunity to ``kick-
start'' activities to train Puerto-Rican students in skills fitting them
for important roles in science, engineering and management.

(2) NAIC itself can see the potential for occasional use of just such an
instrument as HAAT towards its own National Center user research program,
which is open to all scientists of the U.S.A. and elsewhere. Thus, NAIC's
involvement in the development of HAAT as a cutting-edge
research instrument would be both a contribution from it to the training of
Puerto Rican scientists and engineers, and to enhancing the options it
offers to its user base for astronomy, planetary physics and aeronomy.







SCIENTIFIC IMPACT OF HAAT:


[ Note to Murray: This section needs to be shortened - points to bring
across are
VLBI, phase referencing, and the 11.3 m antenna to be brought to AO ]


The 305-m Arecibo radio telescope is the world's largest, most sensitive,
single-dish radio telescope. It is used to carry out observations in radio
astronomy, planetary physics, and the atmospheric sciences, and is equipped
with receivers between $\lambda$6~m and 3~cm, (frequencies between 47 MHz
and 10 GHz). The telescope is also equipped with powerful 430-MHz and 2.4-
GHz transmitters to support atmospheric and radar planetary applications.
In addition to its single-dish capabilities, the Arecibo 305-m radio
telescope also participates in Very Long Baseline Interferometry (VLBI)
observations with the VLBA, HSA, EVN and Global VLBI networks.

The broad capabilities and huge collecting area of the Arecibo 305-m
telescope makes it unique. To further contribute to this and broaden the
range of scientific possibilities it offers its users, while enhancing the
educational and outreach facilities of the Observatory, an auxiliary radio
telescope located nearby would be a huge bonus. Such an instrument would
have scientific capabilities that are both complementary to, and
independent of, the 305-m telescope, and it would
also be made available for educational programs in partnership with Puerto
Rican educational institutions. We foresee the antenna being scheduled in
support of Arecibo user operations with the 305-m telescope for a maximum
of ~10 % of its time. All other time (apart from maintenance) would be
available for integration into the telescope for a maximum of ~ 10 % of its
time. All other time (apart from maintenance) would be available for
integration into the educational and research needs of UPR, and Public
Outreach ventures in collaboration with the UPR and the Observatory's
Visitor Center.

Below, we detail some of the specific scientific and education activities
that can benefit from this auxiliary telescope, HAAT. The following
scientific directions will form the basis of a partnership
between UPR, led by its Humacao campus, and NAIC/Arecibo Observatory.

VLBI -- Phase Referencing:

Phase referencing in Very Long Baseline Interferometry (VLBI) observations
has made it possible to study very weak radio sources by increasing the
effective coherence time for them from, at maximum, a few minutes to hours
(Wrobel et al. VLBA Sci. Memo 24). Currently, some 50 % of VLBI
observations are carried out using the phase-referencing technique.

Phase-referenced observations can be performed in two modes, nodding style,
and in-beam. In nodding style phase referencing, the antennas switch
between the target source and a nearby calibrator, called the phase
reference, every few minutes. The duration of one cycle of observing the
target and phase reference is called the cycle time, and is typically about
5 minutes or shorter. This procedure can be successfully carried out for
observations at 1 GHz and above. However,
at frequencies below 1 GHz the raw coherence times become very short due to
ionospheric effects, requiring the phase calibrator to lie within the
(voltage) primary beam of all antennas in the array.

Both styles of phase referencing encounter limitations with the Arecibo 305-
m telescope. The Gregorian dome, located on a suspended platform, and
sustained by cables, has slow slew rates (24o/min in azimuth, 2o.4 /min in
zenith angle.) Hence, in a typical nodding-style, phase-referenced
observation, where the calibrator could be located 3o or more from the
target, a significant amount of observing time, often ™ 50 %, is wasted
slewing between the two sources, leading to a significant loss in signal-to-
noise ratio. For in-beam phase referencing observations, Arecibo's primary
beam is usually too small to find a satisfactory phase calibrator
sufficiently close to the target. The lowest frequency used for VLBI with
the 305-m telescope is 327 MHz; at this frequency the half-power beam size
is only 15 arcmin FWHM, compared to 2.5 degrees for the 25-m VLBA antennas,
(i.e. a ratio of beam areas of 100:1.)

However, phased-referenced VLBI observations could be performed equally as
well using a small on-site telescope. For nodding-style phase referencing,
this ``auxiliary'' telescope tracks the phase calibrator, while the 305-m
antenna observes the target most of the time, only
occasionally looking at an amplitude calibrator.

A number of frequency bands below 10 GHz would be required on the auxiliary
antenna, these being those used as standards by the VLBI community. While a
separate VLBI backend and recorder may be required for the auxiliary
antenna, it might be possible to time-share a single
system, as is also envisaged for the maser time/frequency standard.

The 11.3-m HAAT antenna:

In searching for an economical solution to obtaining an ``auxiliary''
antenna at Arecibo for use in phase-referenced VLBI (and other roles) and
to be operated in partnership by UPR~(Humacao) and NAIC, we recently
learned that NASA/Canberra Deep Space Communication Complex (CDSCC) had
moth-balled their 11.3-m antenna (DSS-33), earlier used as a HALCA/VSOP
earth station, and were looking for somebody who would be interested in
taking over the dish. This indeed looks a potentially acceptable option for
the auxiliary dish, and we have expressed our interest to NASA and are
actively pursuing acquisition. Below we summarize its expected performance
figures.

Effective Area, Aperture Efficiency & Sensitivity

The 11.3-m antenna gains quoted in NASA specifications are 63.1 dBi at 15
GHz, and 58.0 dBi at 8.45 GHz. These translate to an effective collecting
area of about 64 $\pm$ 1 m$^{2}$, giving an aperture efficiency close to
64\% at both frequencies. This effective area yields a point-source
sensitivity of 0.023 K/Jy. The similar values for aperture efficiency at
these two frequencies suggest that the antenna will work well to at least a
frequency of 15 GHz, (possibly higher; see below), meaning that it will
operate efficiently across the complete frequency range of the 305-m
telescope (327~MHz to 10~GHz).

With a system temperature of T deg K, this would give a system equivalent
flux density (SEFD) of 43.5\,T Jy. For a system temperature of 25-30 K,
this gives an SEFD of 1090-1300 Jy, compared with an SEFD of about 310 Jy
at 5 GHz for a VLBA antenna.

HPBW, RMS Confusion \& Fringe Spacing with the 305-m Telescope:

Taking, (i) standard frequencies from 327 MHz to 30.0 GHz and using, (ii)
HPBW~$\sim 1.22 \times \lambda$/Diameter, (iii) Jim Condon's ``rule of
thumb" formula for rms confusion, and (iv) computing fringe spacing for a
projected separation of D meter gives the values in Table~2. These suggest
that the antenna would need to be able to point with an rms of better than
about 1 arcmin for single-dish operations up to 10 GHz. (The pointing
requirements for VLBI operations are $\sqrt{2}$ more lax.) A separation of
about 1 km from the main dish would give a minimum fringe spacing of about
45 arcsec at L-band should the two antennas be used together
interferometrically.

\begin{table}[tbh]
\begin{center}
\caption{Observing parameters for HAAT at various wavelengths}
\vspace{5mm}
\begin{tabular}{|l|c|c|r|}
\hline
Frequency & HPBW & RMS Confusion & Minimum Fringe Spacing \\
\hline
327 MHz & 5.8 deg & 45 Jy & 3152/D(m) arcmin \\
1.4 GHz & 1.4 deg & 950 mJy & 737/D(m) arcmin \\
2.4 GHz & 48 arcmin & 210 mJy & 433/D(m) arcmin \\
5.0 GHz & 23 arcmin & 29 mJy & 206/D(m) arcmin \\
8.4 GHz & 14 arcmin & 7.5 mJy & 123/D(m) arcmin \\
15.0 GHz & 7.4 arcmin & 1.4 mJy & 69/D(m) arcmin \\
30.0 GHz & 3.7 arcmin & 0.2 mJy & 34/D(m) arcmin \\


Is HAAT Large Enough to Provide Adequate VLBI Phase Referencing?

An appropriate parameter to consider when investigating whether HAAT would
be acceptable for VLBI phase referencing seems to be the minimum correlated
flux density for a VLBA-to-HAAT baseline needed to provide a given signal-
to-noise ratio. The phase error (1-$\sigma$) for a
signal-to-noise ratio of S/$\Delta$S is ~$\sim \Delta$S/S radians, where S
is the source flux density. Hence, a signal-to-noise ratio of 5 would imply
a rms phase error of about 11.5 deg.

We have used the EVN sensitivity calculator to estimate the r.m.s noise
expected for a VLBA-to-VLBA baseline. For a single polarization at a
wavelength of 6 cm, with a bandwidth of 8 MHz and an integration time of 2
min, the VLBA-VLBA baseline sensitivity (1-$\sigma$) is 10 mJy/beam. If
HAAT were to have a similar T$_{\rm{sys}}$ to a VLBA telescope at this
wavelength, then the baseline sensitivity for an 11-m to a VLBA antenna (1-
$\sigma$) should be $\sim$~22 mJy/beam. This implies that, at the 5-
$\sigma$ level, sources brighter than about 110mJy/beam should be suitable
for phase referencing. This would include the majority of sources from the
various sections of the VLBA Calibrator Survey.

Structural and Electronics Parameters

The main shaped quasi-parabolic reflector of the 11-m antenna is based on a
central hub and trusses with 24 panels. All mechanical telescope components
are of aluminum. The surface tolerance is 0.5 mm rms, suggesting that the
antenna will work to $\sim$30 GHz. It has a
shaped-Cassegrain secondary reflector of diameter 1.22 m. The total
structure weight is 6500 lb.

Tracking: Single-channel monopulse

The antenna will come with broadband corrugated horns and associated
receivers and transmitters (output power 1 W maximum at 15 GHz, and 5 W
maximum at 7.2 GHz) at Ku- and X-band having previously been used for down-
linking. The receivers are believed to be have only a single
circular polarization (hand of polarization selectable).




RESEARCH & EDUCATIONAL PROGRAM:



The educational program will be developed under two categories:

One for the under graduate students in applied physics in which the
students will spend a .... (xxx months) of internship at the observatory
working on hardware/software projects in designing and building equipment
for the HAAT. These students will be mentored jointly by the engineers of
the
observatory and the UPR professors.

In the second program, the students in physics and astronomy program of the
UPR will join in the research collaborations undertaken by UPR faculty and
NAIC staff astronomers as described below. The HAAT could also form a
laboratory tool for hands-on astronomy technique courses adopted at the
university.

[Note to Murray: The two paragraphs above need further development with
more specific information about the degree, credits, etc. in consultation
with Rafael et al.]



Research Area-I : Astronomical Projects using Phase Referencing VLBI


Stellar (radio) Astrometry:

Collaborators: Juan Carlos Cersocimo (UPR-HUMACAO), Chris
Salter (NAIC-AO),
Tapasi Ghosh (NAIC-AO),

In a white paper submitted to the NSF ExoPlanet Task Force, Bower et al.
(arXiv:astro-ph/0704.0238v1) explore the possibility of ``Radio Astrometric
Detection and Characterization of Extra-Solar Planets". Utilizing the
better than 100-microarcsec positional accuracy routinely achieved with the
VLBA, they propose carrying out a Radio Interferometric Planet search
(RIPL) that will survey 29 low-mass, active (radio-loud) M-dwarf stars over
3 years. This would have sub-Jovian planet mass sensitivity at distances of
about 1~AU from the star.

They also note that, ``Radio astrometric planet searches occupy a unique
volume in planet discovery and characterization parameter space. The
parameter space of astrometric searches gives greater sensitivity to
planets at large radii than do radial velocity searches. For the VLBA and
the expanded VLBA, the targets of radio astrometric surveys are by
necessity nearby, low-mass, active stars, which cannot be studied
efficiently through the radial velocity method, coronography, or optical
interferometry.''

Current measurement errors are limited by the number of nearby compact
sources that are well above the detection threshold of their observations
and which can be used as reference sources in their differential
measurements. The addition of Arecibo in such surveys would increase the
detection sensitivity by a factor of four, making it possible to venture
into the study of objects with one third of the mass of Jupiter as
companions of similar stellar types. As Arecibo's primary beam is much
smaller than other telescopes, and the slew rate slower, the availability
of HAAT for phase referencing would be highly beneficial for taking such
studies down to thermally emitting stars.

A Broad-impact VLBI Measurement of Trigonometric Parallax of Star Clusters:


Collaborators: Juan Carlos Cersocimo (UPR-HUMACAO), Chris
Salter (NAIC-AO),
Tapasi Ghosh (NAIC-AO),

In an impressive work using the VLBA at 8 GHz, Menten et al. (2007, A&A,
474, 515) have determined the trigonometric parallax of several stars in
the Orion BN/KL region. This has allowed them to derive the most accurate
value so far ($414\pm 7$~pc) for the distance to this
region, about an order of magnitude better than the previous value of
361$^{+168}_{-87}$~pc determined from the optical parallax measurement of a
single star in this complex by Hipparcos. Luminosity-based distance
estimates of star-forming regions could be adversely affected
by poorly known extinctions, and the new radio technique of Menten et al.
is an important way to improve the estimation of distances, and hence
luminosities, with subsequent impact on star-formation theories.

As in the previous case, the inclusion of Arecibo would permit the
extension of such studies to fainter, more distant, star-forming regions.

Pulsar Astrometry:

Collaborators: ?? (UPR??), Jim Cordes ? (Cornell University), Paulo
Freire ? (NAIC-AO),

High-precision astrometry of pulsars over multiple epochs can provide their
basic astrometric parameters: positions, proper motions, and annual
trigonometric parallaxes. Due to the weakness of most pulsars, with duty
cycles of typically $< 10$\%, the participation of Arecibo and phase
referencing is often vital to the success of this exercise.

In respect of positional measurements, it is to be noted that VLBI
estimations are tied to the reference frame of the distant quasars, rather
than the Solar-system frame provided by pulsar timing positional estimates.
This allows fundamental reference frame ties between the Solar-system and
extragalactic (ICRF) frames via measurements of recycled pulsars, which are
highly stable rotators.

Proper motion estimates allow pulsars to be traced back to their birth
sites and, for very young pulsars, associations with progenitor supernova
remnants (SNRs) can be established, providing an independent age estimate
for the remnant. Combined with pulsar distance estimates, proper motion
measurements lead to estimates of space velocities, allowing a study of the
natal kicks imparted to pulsars at the time of their birth.

When a parallax measurement is possible, this yields a model independent
estimate for the distance (and hence velocity) of the neutron star. Such
measurements, (i) calibrate models of the Galactic
electron distribution, (ii) constrain SN core collapse using the velocity
estimates, and (c) for hot neutron stars with optically observed thermal
surface radiation, provide the photospheric size and
thus constrain the equation of state of matter at extreme pressures and
densities.

Detection Experiemnts:

Collaborators: ?? (UPR-HUMACAO), Chris Salter (NAIC-AO), Tapasi Ghosh
(NAIC-AO)

Present-day VLBI offers thehighest sensitivity radio astronomical
observations yet achieved, with
noise levels approaching 1 $\mu$Jy/beam being attained with arrays using
the world's most sensitive telescopes, and in particular the Arecibo 305-m
dish. Hence, the 305-m telescope is being increasingly used in experiments
to detect very weak, very compact, astronomical targets, such as radio
emission from X-ray stars, distant supernovae and their remnants, Gamma-Ray
Bursts, and red-dwarf and other stars. However, for these sensitivity
levels to be reached for targets of very low intensity, it is essential
that the observations use phase-referencing.
VLBI imaging of molecular gas in ULIRGs:

Collaborators: Mayra Lebron (UPR-Rio Piedras), Chris Salter (NAIC-AO),
Tapasi Ghosh (NAIC-AO), Mikael Lerner (NAIC-AO), Robert Minchin (NAIC-
AO)



[ text to be added ...]



Research Area-II : Using HAAT As An Independent Single Dish

Full-Stokes Galactic Plane continuum Surevy with HAAT:

Collaborators: Juan Carlos Cersocimo (UPR-Humacao), Chris Salter (NAIC-
AO), Tapasi Ghosh (NAIC- AO)

The 11.3-m HAAT telescope, together with existing Arecibo backends, will
enable the making of full-Stokes continuum surveys using the cooled dual-
channel receivers that will be built for use with the dish. To set the
context for large-area, full-Stokes, continuum surveys with
HAAT, a compendium of some of the existing continuum surveys made at
different frequencies with full spatial-frequency coverage and similar
resolution to HAAT are given in Table~1.

Full-Stokes continuum surveys of the wider Galactic plane at high
frequencies using HAAT would provide unique databases in a number of ways.
Firstly, they would yield full spatial frequency mapping at a number of
previously unmapped wavelengths, with competitive resolution for such
extended features as the Galactic background emission, HII complexes, and
middle-aged and old SNRs. Comparison with the existing lower frequency
surveys listed in Table~1 would allow accurate estimation of the spectral
index distribution over these features, providing the ability to perform
accurate thermal-nonthermal separation on angular scales between
1$^{\circ}$ and $<$10~arcmin. This would allow the study of energy
injection to the ISM and energy losses of
relativistic particles associated with SNRs, and the mechanisms of vertical
transport and diffusion of energy from the disk of the Galaxy into the halo
and intergalactic space.

Simultaneously recorded linear polarization measurements are of especial
importance. The appearance of the polarized sky at wavelengths $\geq
\lambda$21\,cm is complex. Westerbork at 327 MHz for high Galactic
latitudes and the Canadian Galactic Plane Survey at 1.4 GHz have shown that
there is little relationship between total intensity and polarization
structures. In fact, for the diffuse Galactic synchrotron emission, the
bulk of the area of the Galactic Plane imaged on arcminute scales at L-
band reveals highly structured polarization features with no counterparts
in Stokes I. The accepted interpretation of this is that although the
Galactic synchrotron emission is intrinsically quite smooth, differential
Faraday rotation in the intervening magneto-ionic medium, (the Faraday
Screen), imposes fine structure on the polarized emission. In other words,
the
low-frequency polarized sky is dominated by propagation effects rather than
by intrinsic emission structure. This field of study is now moving from
phenomenology to astrophysics.

The signals produced by the Faraday Screen are rather weak, and the limited
surface brightness sensitivity of interferometers samples only the
strongest. Even for these, the derived rotation measures (RMs) are noisy
due to low signal-to-noise per channel. Moreover, the lack of zero-
spacings in interferometric observations leads to complications in
interpretation. The high brightness sensitivity of HAAT, coupled with afew
arcminute beam size at high frequencies, promises major advances in the
study of the magneto-ionic medium. At these frequencies( \gapp~10~GHz) the
effects of Faraday rotation become tiny ($\Delta\theta \propto \nu^{-2}$)
and HAAT can measure linear polarization whose position angles are
essentially those intrinsic to the emission. These can provide both
intrinsic directions of magnetic fields, and a database against which the
lower frequency polarization distributions can be definitively interpreted.

In previous studies of the Faraday Screen, the spectral signatures of the
polarized intensity have been examined to seek only a single RM value per
image pixel. Such a value corresponds to a RM in the foreground of the
dominant polarized emission component along a given sight-line. However,
the Faraday Screen is spread out in depth along each line of sight, with
different regions of polarized emission at different distances along the
sight-line contributing to the observed spectrum with their corresponding
foreground Faraday rotation signature. Because of depolarization effects,
bandwidth integrated polarization will show a lower degree of polarization
than that intrinsic to individual slabs. With an appropriate combination
of observing frequency, bandwidth and spectral resolution, it should be
possible to perform Faraday tomography, wherein the spectral polarized
intensity modulations along a given sight-line can be transformed to a set
of polarized intensities as a function of Faraday depth (i.e. RM). Thus, it
should be possible to derive a polarized-intensity data cube (quite like a
spectral-line data cube) with two dimensions being the
sky coordinates and the third being RM. High-frequency images from HAAT
would be invaluable in pursuing this endeavor.

Away from the Galactic plane, the high latitude regions contain several
well-known non-thermal emission structures. Most notable is the North
Polar Spur (Loop 1), an object that contains rich small-scale structure,
both on its main arc and in internal ridging (Fig.~\ref{fig4}). Above $b =
45^{\circ}$, even low resolution Dwingeloo measurements have shown this
nearby ($\sim$100 pc distant), old SNR to be $>$\,70\% linearly polarized
at 1.4~GHz. HAAT images at a few cm wavelength would directly reveal
magnetic field directions in this object whose RMs are low.

We should specifically mention the L-band Arecibo GALFA Continuum Transit
Survey (GALFACTS), which is being made by an international consortium of
astronomers led by Prof. Russ Taylor (U. Calgary). This full-Stokes survey
of the whole sky observable with the 305-m
telescope, covers the frequency range of 1225 -- 1525~MHz, with 8192
frequency channels to study both the total-intensity and polarized
distribution of the celestial radiation. At L-band, the effect of Faraday
rotation on the linearly polarized radiation is considerable, the GALFACTS
precursor surveys demonstrating complex structure both spatially and in
frequency. A continuum survey at much higher frequency, but similar
resolution (HPBW $\sim$ 4 arcmin for GALFACTS), would be invaluable when
combined with GALFACTS both to allow thermal-nonthermal separation, and to
aid Faraday tomography of the linear polarization data. The same situation
exists in respect of that part of the Southern Galactic Plane Survey, an L-
band continuum survey being made with the Parkes radio telescope in
Australia (HPBW $\sim$ 15 arcmin; Haverkorn et al 2006). HAAT surveys would
also provide the vital low-spatial frequency data for future
interferometric full-Stokessurveys.



Synergy with GLAST

The main processes producing $\gamma$-rays in our Galaxy are believed to
be, a) brehmsstrahlung from the interaction of cosmic-ray electrons and the
interstellar gas, and b) the decay of neutral pions produced in
interactions between the gas and cosmic-ray protons and heavier nuclei.
The former is thought to dominate at $< 1$~MeV, and the latter at energies
higher than this. Similar distributions of $\gamma$-rays are found at low
latitudes in both energy ranges, suggesting that the cosmic-ray heavy
particle-to-electron ratio is constant over the
Galaxy. If so, the $\gamma$-ray emissivity, $\eta_{\gamma}$, is
proportional to the product of the cosmic-ray intensity and the $total$
(i.e. neutral and ionized atomic gas, plus molecular gas) gas density
($\rho$);

\begin{equation}
\eta_{\gamma} \propto N_{0}\rho
\end{equation}

where the cosmic-ray energy distribution is,

\begin{equation}
N(E)dE = N_{0}E^{-\Gamma}dE
\end{equation}

Now, for the synchrotron component of the Galactic radio emission, the
emissivity is,

\begin{equation}
\eta_{R} \propto N_{0}B_{\perp}\!\!^{(\Gamma +1)/2}
\end{equation}

where $B_{\perp}$ is the magnetic field strength perpendicular to the
line of sight.

The Galactic distributions of the three quantities, $N_{0}$, $\rho$ and
$B$, are all of considerable astrophysical interest. Arecibo can contribute
significantly to a knowledge of $\rho$ over the accessible sky as the GALFA
consortium will provide, a) the 2-dimensional distribution of HI, while the
thermal-nonthermal separation of the continuum emission mapped by the HAAT
and GALFACTS continuum surveys will provide the 2-D distributions of b) the
thermal emission from HII and c) the non-thermal synchrotron emission. The
2-D distribution of the molecular gas is already available from CO surveys
of similar resolution. Hence, combining Arecibo HAAT and ALFA work with
other radio data and the high-fidelity GLAST $\gamma$-ray background images
will provide the necessary information to ``unfold'' the 2-D distributions
and derive the Galactic distributions of $N_{0}$, $\rho$ and $B$. This
would represent a major contribution to our understanding of the detailed
distribution of the magnetic field and cosmic rays in
the disk of our Galaxy.




Pulsar timing:

Collaborators: ?? (UPR-Humacao), Paulo ?? (NAIC-AO)

(If this is required, Paulo should be asked to expand it.)

The majority of pulsars are too weak to be satisfactorily timed with
an 11-m dish. However, timing observations of the strong Crab and Vela
pulsars would complement dedicated measurements being made to detect
timing glitches in these objects (e.g. Lyne et al., 1996, Nature,
381, 497 \& Lyne et al., 1993, MNRAS, 265, 1003). The signals received
can be piped back to the control room for processing with existing
Arecibo backends.


Research Area-III : Astronomical Projects using the 305-m telescope

Collaborators: Carmen Pantoja (UPR- Rio Piedras) , Robert Minchin (NAIC-
AO)

ZOA science goals (or some part of ALFAALFA project, ----- text to be
develope







2





EDUCATION AND OUTREACH PROGRAM


Collaborators:


As a semi-dedicated instrument for the research and education needs of
Puerto Rican universities, an integrated program of teaching, technical
development and research will be developed around HAAT between a Puerto
Rican Astronomy Consortium (PRAC), and the NAIC. As a radio telescope, HAAT
would be available for observations 24 hours per day, subject only to
routine maintenance constraints.

On installation of the telescope, a considerable number of engineering and
software tasks would need to be accomplished to bring HAAT on-line,
offering excellent experience for students of the scientific, electronics
and computing departments of PRAC institutions. Receivers need to be
constructed, the drive system and other software developed, and remote
operations implemented, the latter being essential for the classroom
utilization of HAAT, the performance of extended thesis projects, and for
the use of HAAT in ``hands-on'' public outreach sessions coordinated by the
UPR and the Arecibo Observatory's ``Angel Ramos Foundation'' Visitor
Center. Observatory staff would be available as a valuable resource to the
faculties of PRAC institutions in terms of research projects centered on
HAAT, lecture courses centered around HAAT-related topics, co-supervision
of student research, and participation of Puerto-Rican students in the
Arecibo REU and other summer-student programs. Projects using HAAT could
also be incorporated in the annual RET program for Puerto Rican science
teachers run by the Visitor Center.

Presently, Puerto Rico offers only very limited access to local
astronomical instruments for education, training and research. The high
annual humidity, the hurricane season, and the elevated annual rainfall all
mitigate against significant optical facilities being placed on the island.
However, centimeter/decimeter radio observations placed on the island.
However, centimeter/decimeter radio observations are largely unaffected by
weather conditions (hurricane passages apart!) In addition, the presence of
both HAAT and the Arecibo 305-m radio telescope, the world's largest single
radio telescope, on the island will represent a truly unique opportunity
for an expansion of astronomical activities within the island's
universities that could help transform a community of 4 million under-
represented U.S. Citizens into the academic envy of many other parts of the
nation!





5 BROADER IMPAct of the Proposed Project


HAAT as an Independent VLBI Element

HAAT could be a very useful instrument in its own right for VLBI support,
especially as it will have ``full sky coverage''. For many experiments,
this would complement the N-S baseline between LA and PT, by providing an E-
W baseline of similar length between itself and the SC VLBA antenna. HAAT
could be used when the 305-m telescope was either not available, not needed
(stronger targets, or those needing greater uv-coverage than the 305-m can
provide), or otherwise inappropriate (e.g. declinations not covered by the
305-m dish.)

It is to be noted that the geographical position of the fully steerable
HAAT could be measured interferometrically with high precision, and the
(presently somewhat uncertain) position of the 305-m steerable HAAT could
be measured interferometrically with high precision, and the (presently
somewhat uncertain) position of the 305-m determined from this via
surveying, etc.


Geodetic VLBI (??)


The ``International VLBI Service for Geodesy \& Astrometry'' (IVS) recently
laid down a set of guide lines for the next-generation of geodetic VLBI
measurements of station positions and earth orientation parameters. These
are called ``VLBI\,2010''.The aim is to achieve 1~mm positional accuracy on
intercontinental baselines with a 24-hr turnaround for results. However,
there is insufficient funding for an international network at present, and
the geodetic community is interested in any telescope that could
participate. As is being planned for HAAT, the antenna needs to have
minimal horizon obstruction, and be sited on good bed-rock.

The VLBI\,2010 requirements specify a telescope design of 12 meter
diameter, close to the size of HAAT, with a system temperature of about
T$_{\rm{R}} = 45$\,K (SEFD $<$2500~Jy. A frequency coverage of 2 - 18~GHz
will ultimately be needed, a range that can be covered by HAAT. Dual-
frequency operations are a requirement to allow for ionospheric correction.
An eventual data recording rate of 8 - 16 Gbps is being set as a goal, and
is consistent with NAIC development plans for its VLBI backend; Recording
at a rate of 4~Gbps was recently made with the 305-m telescope using a
borrowed digital backend, and dual state-of-the-art Mk5 recorders. Much of
the data transfer is envisaged as being over the internet (e-transfer), and
Arecibo is already the leading player in N. American astronomical eVLBI.

Arecibo would be attractive as it is situated on the Caribbean techtonic
plate. This plate is very complicated, and accurate measurements of
velocities in a global frame are most valuable. Currently, the 25-m VLBA
antenna on St. Croix is available to the geodetic array, but only on
occasions per year. For each geodetic session, the geodetic community would
need 24 hr participation. The minimum involvement required is once per
month, though once per week would be welcomed. While the geodetic
community intend extending their frequency coverage to Ka band eventually,
this would not be necessary for some while. They would require 2-bit
recording, and early recoding rates of (say) 2 Gbps.

To participate in geodetic VLBI a cable-delay system (i.e. A ``round-trip'
phase measurement) will be needed as system delays need to be tracked at
the mm-level. Diurnal effects should be monitored, and the receiver has be
as stable as possible. A dual-frequency GPS receivers should exist close
to the antenna, as is already the case for the planned HAAT site. Geodetic
operations are the responsibility of the individual antennas. Analysis
centers exist around the World, with some being based at universities. It
is likely that UPR could become involved? We note that
the analysis of VLBI data is simple compared to that for GPS data. Further,
while GPS is good for measuring regional motions (over $\sim$1000 km), VLBI
can provide the tie to more distant points with better accuracy than GPS








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