Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/STSCI/MARCH92.TXT

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SCIENCE NEWS

COSMOLOGICAL SIGNIFICANCE OF GHRS OBSERVATIONS OF D/H TOWARDS CAPELLA

The ease with which deuterium can be destroyed in nuclear reactions implies
that essentially all of the deuterium now present in the Universe was
created in the first few minutes of the Big Bang. In April 1991, Jeffrey
Linsky and colleagues on the GHRS Team obtained GTO observations intended
to measure the deuterium/hydrogen ratio in the local region of our Galaxy.
The goal was to infer the primordial ratio and densities at a very early
stage of the Universe, before the deuterium was destroyed by nuclear
reactions in stars.

Using the Echelle-A grating of the GHRS, the GHRS Team observed the nearby
(12.5 pc) bright star Capella (alpha Aurigae). Absorption by interstellar
hydrogen and deuterium Lyman a lines, which are separated by an amount
corresponding to 80 km/s, can clearly be seen  as a broad feature and a
narrow feature 0.33 ANGSTROMS to the left, respectively, in the spectrum at
the left.

The broad chromospheric Lyman a emission line from Capella is the
background light source for this experiment. Analysis of this spectrum and
the Echelle-B spectra of the interstellar MgII and FeII lines provide
extremely accurate measurements of the interstellar temperature, T = 7150
+/- 150 K, and turbulent velocity, xi = 1.63 +/- 0.03 km/s, for this
apparently simple line of sight.

The measured hydrogen and deuterium column densities are NHI = 1.80 +/- 0.2
X 1018 cm-2 and NDI is 3.00 +/- 0.03 X 1013 cm-2. This means the atomic
deuterium/hydrogen ratio is D/H = 1.65 (+/- 10%) X 10-5 for this line of
sight.

This ratio lies at the mean of all of the previous IUE and Copernicus
measurements, but is far more precise than previous work for the Capella
and other lines of sight. The new data suggest that the local region of the
Galaxy is well mixed, but further observations╩for other lines of sight
are needed to confirm or modify this tentative result.

      The measured local D/H ratio places a hard upper limit on omega
baryon< 0.12 (for Ho=50) or < 0.03 (for Ho = 100). If the primordial D/H
ratio is three times the local value, as suggested by published Galactic
evolution models that include astration and infall of primordial or
partially astrated material from the Galactic halo, the ratio of the
density to closure density is omega baryon< 0.06 or 0.015 for  H0=50 or
100, respectively. Unless the assumptions in the standard Big Bang theory
are very far off or the  Universe is dominated by cold dark matter, the
deuterium data provide a

-Jeffrey L. Linsky

HST DISCOVERS YOUNG GLOBULAR CLUSTERS IN NGC1275

   Recent WF/PC images of the galaxy NGC 1275 have revealed what appears to
be a population of young globular clusters (see photo at right). The WF/PC
GTO observations show about 50 bright, blue sources near the center of this
galaxy (Holtzman et al. 1992, AJ, 103, 691). The colors and magnitudes
suggest that these objects are young star clusters. However, the resolution
of HST also shows that these clusters are very compact. Most of the
clusters have radii less than about 15 pc, much smaller than ordinary star
clusters, but characteristic of globular clusters.

The curious aspect of this discovery is that most globular clusters are
extremely old. There is some evidence of other young globular clusters
around nearby galaxies, but there has been much debate as to whether these
are " true"  globular clusters or simply massive star-forming regions that
will eventually form open clusters or dissolve entirely. The observations
of Holtzman et al. show definitively that genuine globular clusters can
form at the present epoch.

While this realization is an important step forward in our understanding of
globular cluster formation, the observations of NGC 1275 give further clues
to the conditions under which globulars form. In particular, the WF/PC
images reveal disturbances and structure in the underlying galaxy that may
have been caused by a merger with a smaller galaxy. Holtzman
et al. conclude that this merger occurred at about the same time as the
young globular clusters formed. This suggests that galaxy mergers may
actually trigger globular cluster formation.

It has often been suggested that elliptical galaxies form by the merger of
two or more spirals. The biggest stumbling block to this idea was the
observation that ellipticals have far more globular clusters than spirals.
It was recently shown (Ashman and Zepf 1992, ApJ, 384, 50) that globular
cluster formation in mergers is theoretically plausible, and that a
sufficient number of clusters can form to explain the excess around
ellipticals relative to spirals. This removes the obstacle to a merging
origin for ellipticals. The HST observations of NGC 1275 suggest that
globular clusters could indeed form in galaxy mergers.

-Keith Ashman

HSP OBSERVATION OF A STELLAR OCCULTATION BY SATURN' S RINGS

A prime objective of the High Speed Photometer (HSP) team' s GTO program is
the observation of stellar occultations by planets and other solar system
objects. This technique can probe the structures of planetary atmospheres
and rings with remarkably high spatial resolution, since the starlight
probes the occulting object before being blurred by atmospheric seeing or
the point-spread function of the telescope.

Spatial resolution of stellar occultation data depends on Fresnel
diffraction by sharp edges in the rings and the projected diameter of the
star at the distance of the occulting planet. At the distance of Saturn,
for example, the resolution is 2 km, equivalent to an angular resolution of
0.0003 arcsec. With smaller focal plane apertures than can be used with
ground-based observations, the HSP can obtain occultation data more
routinely, opening the way for systematic studies in several
areas-including planetary ring dynamics.

On 2-3 October 1991, Saturn occulted the star GSC6323-01396 on its way
toward the stationary point of its retrograde loop. This unusually slow
occultation was observed with the HSP over a period of 20 hours (13 orbits)
during ring emersion. Earth occultations, SAA passages, and guide star
reacquisitions reduced the actual exposure time, for an exposure efficiency
of 34%. The losses due to SAA passage were minimized by resuming data
collection after SAA on two of the orbits.

    Whenever possible, simultaneous two-color photometry was obtained using
the HSP' s photomultiplier tube (PMT, 7500 ANGSTROMS) and visible (VIS,
3200 ANGSTROMS) detectors with an integration time of 0.15 sec. Although
the star is not extremely bright (V = 11.9) compared with Saturn' s rings,
its angular diameter is correspondingly small, so that the radial
resolution of our observation was determined by diffraction (~2 km, the
Fresnel limit).

Two motions determine what parts of Saturn' s rings are traversed by the
starlight: parallax due to the orbital motion of the HST, and the relative
motion of Saturn and the Earth. The former causes the apparent position of
Saturn to move in a small ellipse relative to the star, and the latter
stretches these ellipses out into the " curlicues" seen in the accompanying
diagram (top right).

Since occultation observations are inherently time-critical, scheduling
this observation was a challenge. Instead of acquiring the occultation
target star, which was swamped by light from Saturn, there was an onboard
acquisition of an offset target (1.5 arcmin away) and then the target star
was acquired using a blind offset. This maneuver required knowing the
separation of the two stars to better than 0.2 arcsec in order to place the
target in the 1- arcsecond science aperture.

Because the planet and rings are very bright at the observing wavelengths,
they dominate the signal received by the HSP. In order to monitor the
transmission of starlight through the rings, that strong planetary
background must be subtracted. Before and after the occultation
observation, the HSP aperture was scanned across the face of Saturn and its
rings several times, to quantify the background.

Scanning the (moving) telescope across Saturn (itself a moving target) is
one of the most complex tasks the HST has been called upon to perform.
Spacecraft commanding difficulties have unfortunately reduced the amount of
useful data available from the attempted mapping of the parallax-broadened
stellar path. Much has been learned from this observation and new
procedures will insure better coverage for future events.

    This observation of Saturn yielded data covering most of the ring
system, from the inner edge of the C Ring, through the B and A rings and
the tenuous Cassini Division separating them, and out past the F Ring. The
complicated apparent motion of the star behind the rings was very useful in
that it provided multiple passes across some features. There were double
passages through some very interesting radial regions, such as the
azimuthally variable Keeler Gap, in the outermost A Ring (shown in the
inset, bottom right). Comparison of the two Voyager occultation
experiments, which sampled a different time and azimuth in the rings,
demonstrated variation in the Keeler Gap width and elicited the study of a
peculiar wave along the inner edge of the gap. The dynamical cause of this
wave is not yet resolved and additional information, including HST data, is
crucial to our understanding of what is most likely an interaction between
multiple satellite resonances.

The HSP team hopes to observe at least five more occultations by Saturn
before the instrument is removed to make room for COSTAR.

-Amanda Bosh, Maren Cooke, & Jim Elliot



OBSERVATORY NEWS

MESSAGE FROM THE DIRECTOR

Over the past few months, the Space Telescope Science Institute has worked
closely with the HST Project at Goddard Space Flight Center to implement
scientific recommendations regarding priorities in maintenance and
refurbishment of the HST mission. All major hardware necessary for the
planned late-1993 servicing mission (WF/PC II, COSTAR, and Solar Arrays)
appears to be on track.

   A Critical Design Review of COSTAR was held in December 1991 at Ball
Aerospace. System performance analysis, documented in 294 engineering
reports, has verified all aspects of performance. The COSTAR design will
meet its image sharpness and encircled energy requirements. First delivery
of the correcting optics has shown better-than-required figure conformity
and smoothness. Plans for testing and mission operations are now in
progress.

A great deal of work is being devoted to simulating on-orbit alignment,
clearly one of the most delicate procedures in the deployment.

STScI has now finished the Cycle 2 proposal evaluation process. After a
thorough in-house review and a few adjustments to the Telescope Allocation
Committee (TAC) recommendations, letters of notification were sent to all
proposers. The work of the review panels and TAC this year was made heavier
than usual by NASA' s request for advice regarding proposed Guaranteed Time
Observer (GTO) augmentations, as well as by the large number of General
Observer (GO) proposals. Given the limited amount of HST observing time
available, we were able to accept only a fraction of the meritorious
proposals submitted. This has understandably given rise to much unhappiness
in the community, some questions about the degree of attention given to
each proposal, and some concerns on how the relative balance of time
allocation between disciplines can best be set. We have carefully noted
suggestions about improving the process and will discuss them with the
advisory committees of AURA. (For more details of the Cycle 2 results, see
the articles beginning on p. 20.)

More than 40 scientific contributions based on HST results were presented
at the recent AAS meeting in Atlanta. The Educational and Public Affairs
(EPA) group at STScI helped  NASA and individual scientists in publicizing
these results. It issued eight new press releases for the international
media, orchestrated several well- attended press conferences, had a major
presence in the AAS press room, and helped science journalists interpret
some of the more difficult (usually spectroscopic) HST findings. The result
was superb and positive press coverage, in both the print and electronic
media; coverage on CNN was particularly heavy and featured several HST GTOs
and GOs.

The STScI mounted two major exhibits at Atlanta, one highlighting our many
varied educational programs, the other describing and demonstrating
available user services, spanning proposal submission through data
reduction. Both exhibits attracted much attention from the assembled
astronomers, increasing numbers of whom are using the Institute' s
educational and data reduction products at their home institutions.

It appears that the steady " drum beat"  of science results from the Hubble
Space Telescope is beginning, slowly but surely, to convince large segments
of society that HST is returning world-class science. STScI will continue
to present HST science to the public and to educators in the most
professional and scientifically accurate manner possible.

-Riccardo Giacconi

COSTAR UPDATE

Work on the Corrective Optics Space Telescope Axial Replacement (COSTAR) is
proceeding on schedule. COSTAR will replace the High Speed Photometer in
the first servicing mission and will deploy corrective elements into the
optical paths in front of the Faint Object Camera, Faint Object
Spectrograph, and Goddard High Resolution Spectrograph. This is expected to
remove the effects of spherical aberration in the HST primary mirror,
restoring the original design performance of the scientific instruments
(see article on p. 2 of the December 1990 Newsletter).

A very successful Critical Design Review (CDR) for COSTAR was completed in
December 1991. This critical program milestone was carried out on schedule
and one year from the date of the HST Strategy Panel recommendation to NASA
on building COSTAR. NASA and Ball Aerospace, the COSTAR Prime Contractor,
deserve a great deal of credit in accomplishing the extensive work to date
on such a challenging schedule.

    The CDR panel recommended that COSTAR proceed as planned. The only
significant issue raised as a result of the CDR was concern with the torque
of the small motors used to tip, tilt, and focus the spherical M1 mirrors.
The CDR design calls for motors of less than 1 in-oz of torque. These
torque limits are the result of space and operating temperature
limitations. While the torque margin for these motors appears adequate,
members of the review panel were uncomfortable with less than 1 in-oz. The
design was changed to alleviate these concerns by adding a contingency mode
that delivers a torque of greater than 1 in-oz. There will be an operating
restriction on how long the motors can be run continuously in this case.
This should have no effect on the instrument operations and would only
result in a longer time for initial alignment.

Key elements of COSTAR are the five pairs of small corrector mirrors. These
mirrors are considered quite difficult to produce and were identified as
high risk early in the program. Initially three vendors started in parallel
to produce these optics. Early this year, optics for the GHRS were
delivered from Tinsley Laboratories, Inc. Testing showed these optics to be
of excellent quality, exceeding the requirements for both wavefront error
(better than 1/100 wave rms) and surface roughness (4-5 ANGSTROMS rms). The
FOS mirrors have now been figured and also exhibit similar excellent
performance. Progress on the optics for the FOC is also good. These optics
should be completed in March 1992 with acceptance testing planned for
April.

An extended progress review on the structural and thermal model of the FOC
(FOC/STM) was held by the European Space Agency at MATRA in Toulouse,
France in January 1992. The FOC/STM is an exact model of the Faint Object
Camera and will be an important element in the testing of COSTAR. Excellent
progress is being made by MATRA in assuring that this model exactly
replicates the on-orbit FOC. The Laboratoire D'Astronomie Spatiale (LAS,
Marseille, France), who aligned the FOC now in orbit, will be doing the
alignment of the optical system in the FOC/STM. Using an aberrated beam
simulator and a COSTAR simulator, LAS will verify that the FOC/STM is
properly aligned and corrects the spherical aberration. LAS will also
explore the effects of various misalign-ments on the FOC/STM images. ESA
appears to have no difficulty in completing the work necessary to deliver
the FOC/STM to support the COSTAR testing on schedule.

-Jim Crocker

PARALLEL OBSERVATIONS

WITH HST

One observing technique planned to improve HST scientific return is the use
of the cameras (FOC and the WF/PC) in parallel with the prime observations
made with other Science Instruments (SIs). This technique is most useful
for survey programs, where there is no a priori need to identify specific
targets.

For these programs, the parallel observations cover fields a few arcminutes
from the prime target. While the spherical aberration has affected the
scientific objectives that can currently be accomplished with parallel
observations, the technique still increases the return from the telescope,
and will be even more valuable when the optics are returned to original
specifications via WF/PC II and COSTAR.

  The ability to plan and execute parallel observations with the cameras
has now been implemented in the HST ground systems and verified with an
actual test with the telescope at the beginning of January 1992.

The technical problem for the ground system was the management of the
onboard data paths between the SIs and the Science Data Formatter (SDF) and
the Science Tape Recorder (STR). There are three available onboard
bandwidths for the data output from the SIs: 4, 32, and 1024 kbps. The SIs
and the SDF, which is the mechanism for setting the onboard bandwidth, must
be managed so that the data output from the SIs does not exceed the assigned
value.

The SDF supports the parallel readout of all the SIs simultaneously, but
the timing relationship between the SIs and the SDF changes as the overall
load on the SDF changes, due to other SIs reading out. This can cause
readouts to take considerably longer than normal, and the impact of the
slower readouts must be accounted for in operating the SIs to ensure the
readout is completed before the next activity begins.

The initial implementation of the Science Planning and Scheduling System
(SPSS) did not schedule onboard activities at this level of detail. SPSS
planned the total time period exposure, but the details of the filter
motions, electronic setup, exposure, and data readout were implemented in
the science commanding subsystem.

The primary requirement in this implementation was that SPSS allocate
enough time for all the activities which the commanding subsystem later
inserted. While this version of SPSS precluded parallel observing, the
simplification was necessary in order to get the ground system ready to
support HST operations at launch.

   Upgrading the planning systems has been part of the long-range STScI
plans since well before launch. In order to implement a parallel observing
capability, there have been substantial changes to all the planning
portions of the STScI ground system.

The major change was to add a lower level of planning code to the SPSS
system so that it could plan parallel exposures to meet the requirements
for managing the onboard data paths. This includes upgrading the onboard
data rates in some cases, planning exposures so that readouts avoid each
other in other cases. These changes affected over 25% of the modules in
SPSS, a system with 400,000 lines of code.

The science commanding system also had to be modified to react to the new
structures provided by SPSS, especially the data readout commanding. The
RPSS and PEP proposal processing systems were modified for changes in the
input proposal syntax for parallels, and the TRANS subsystem required
substantial modification to populate the new flags and data fields required
by SPSS. The entire system required substantial end-to-end testing, both to
verify the success of the changes and to ensure that previously working
capabilities were not inadvertently affected.

The check-out period culminated in a test with the HST on 6-8 January 1992.
During this test, 17 exposures from the Medium Deep Survey were scheduled
in parallel with an FOC observation of 3C273. All the WF/PC parallel
exposures were successfully executed, including those which resulted in
simultaneous readouts from both SIs.

The current implementation of parallel observations has focussed on the
WF/PC and the FOC. The planning system will now schedule WF/PC parallel
exposures with the FOC, FOS, HSP, and FGSs, and will manage parallel
readouts with the FOC and FGSs. When the FOS or HSP are the prime
instruments, then the scheduling system will arrange the WF/PC parallel
readouts to avoid the prime readouts. When the FOC is used as a parallel
SI, the planning system will schedule the FOC readouts to avoid the other
SIs readouts.

In some situations, the requirement for avoiding parallel readouts (for
some SI combinations) will limit the number of parallel exposures in an
orbit. This is not likely to be a large limitation, since most parallel
programs are likely to take a few long exposures rather than many short
exposures.

With the success of the test in January, the Science Programs and
Operations Divisions have begun planning routine use of parallel programs.
The first of these will begin executing in March/April 1992.

-Rodger Doxsey

SCHEDULING AND OBSERVING EFFICIENCY

The first 18 months of HST operations were characterized by many surprises,
real-time reactions, and a steep learning curve. Now that successful
observations have become more or less routine, improving the efficiency of
HST science operations has become a high priority at the STScI.

Some efficiency improvements involve changes in the actual operation of the
spacecraft and its instruments. Others will come from optimizing STScI' s
long-range planning capabilities. Two study groups have been established
within the STScI to address these efficiency questions: the Observing
Efficiency Task Force (OETF) and the Scheduling Efficiency Working Group.
Both groups have started fact-finding activities, and their efforts are
expected to lead to incremental efficiency improvements over the next year
of HST operations.

The OETF is currently investigating technical issues that affect HST
observing efficiency. Several areas where significant improvements can be
made in the scheduling software and instrument commanding have been
identified. During the coming months, the task force will explore various
solutions and begin their implementation.

HST observing efficiency can also be increased with more efficient 6-month
and 1-year long-range observing plans. Many HST observing programs are not
time-critical and so have sufficient flexibility to be scheduled at the
optimal (i.e., most efficient) time of year.

To achieve an optimal long-range plan, the pool of candidate observations
available at one time must be increased. The current throughput of Phase II
observing proposals, from receipt at STScI through creation of flight
candidate scheduling units, is insufficient for this purpose.

  The Scheduling Efficiency Working Group (SEWG) is considering
improvements in the areas of management, procedures, communications, etc. -
" real people areas"  - to ensure that the flow of information and
proposals from the user to the STScI and within the STScI is as smooth and
efficient as possible. The SEWG will examine the current proposal flow and
throughput, and will recommend near-term and long-term methods of improving
the end- to-end proposal processing procedures.

The SEWG efforts are intended to complement those of the OETF, with close
coordination between the efficiency study groups yielding the maximum
scientific output of HST. The resulting improvements to HST observing
efficiency will be described in more detail in future newsletters.

-Peg Stanley & Bill Oegerle

HST OBSERVATORY STATUS

    There has been little or no change in the performance of the HST flight
systems since the last Newsletter. The four gyros in use are operating
well, with no further anomalies. The basic spacecraft support systems, such
as pointing control, thermal control, commanding and communication, and
onboard computers are all operating properly and supporting the scientific
observations.

    A major improvement has been made with instrument operations, namely
the development of a method to restore GHRS Side 2 to normal operations.
The failure analysis of the GHRS Low Voltage Power Supply (LVPS) on Side 1
has indicated that the problem was caused by a failed solder joint on a
particular power distribution terminal on one of the boards in the power
supply. This particular terminal supplies power to the LVPS used for Side 1
operations and to a standby power supply which is used, among other things,
to route data from Side 2 to the spacecraft data

handling systems (when the spacecraft is configured to operate with its "A"
side redundant equipment, which has been the case since launch).

When the failure first appeared it was intermittent. As soon as the failure
appeared, Side 1 operations were halted because of the possibility that
intermittent operation of the LVPS while high voltage is on could cause a
failure in the digicon detector. (A failure of this type occurred during
the development cycle.) The intermittent operation of the standby power
supply resulted in data from Side 2 being lost, but did not put the Side 2
detector at risk.

In November 1991 a background engineering test was devised and uplinked to
the HST. This test used the onboard computer to command a data readout from
the GHRS through the intermittent interface every 5 minutes, except during
periods when the interface was being used by other SIs for science
observations. The purpose of the test was to try to determine whether the
intermittency was purely random or correlated with any onboard variable.

As the test ran, it appeared that the contact would remain solid, at least
for the standby power supply, if the temperature in the region of the power
supply was maintained above about 5í C.

The STScI has modified the operational procedures for the GHRS to leave the
Side 2 LVPS on all the time, with the result that the temperature stays
above the magic value and the solder joint provides sufficient current to
the standby supply to operate the Side 2 data interface. Using this
technique, observations with GHRS Side 2 have been scheduled since late
December 1991, with no failures due to the intermittent solder joint.

A question remains with whether or not Side 1 operations can be resumed.
Given the nature of the solder joint failure, it is not clear that
successful operation of the standby supply implies successful operation of
the Side 1 LVPS is possible. The Side 1 LVPS has not been turned on since
the first incident in August 1991 because there is a small, but finite,
possibility that turning it on could lead to a failure that would damage
the standby supply, hence making Side 2 operations impossible again.

As analysis and test of bread-board components has proceeded, the concern
with turning on the Side 1 LVPS has receded but not disappeared completely.
There are plans for bench tests with a spare detector to determine whether
a quick cycling of high voltage would damage the current generation of
detectors. The STScI, the GHRS IDT, and the HST Project are actively
considering the pros and cons of attempting operations with Side 1.

-Rodger Doxsey

HST FOCUS

The collimation of the HST Optical Telescope Assembly (OTA), meaning the
relative positions of primary and secondary mirrors, determines the point
spread function seen in HST data. Since launch, the position of the
secondary has been adjusted a number of times by commands from the ground,
and has also been affected by the natural shrinking of the OTA. This
article describes the collimation history of the telescope and the
implications for HST data.



Definition of Best Focus

The nominal best focus setting for HST has been defined as the point that
gives the maximum encircled energy in a 0.1-arcsecond radius aperture in
the FOC at 486 nm. This represents a compromise between the needs of the
spectrographs and the FOC and WF/PC. This focus setting is about 12.2 mm
from the paraxial focus in the OTA F/24 image space, as illustrated in the
first figure (p. 7).

We aim for this point with an error of about 5 microns of secondary mirror
motion. This error corresponds to 0.55 mm in the focal plane, a change in
geometric image diameter of 2%, and a loss in encircled energy in 0.1
arcsec of less than 1% near the maximum.

There is some evidence from WF/PC images that " breathing"  of the
telescope structure is causing focus shifts with an amplitude of 2-4
microns equivalent secondary motion. The effect probably does originate at
the OTA secondary as it would correspond to unreasonably large motions of
the WF/PC optics. The noise from an individual focus determination is also
at the 2-4 micron level.



Mirror Move History

The history of the OTA secondary mirror position is important for comparing
observations taken at different epochs, constructing model point spread
functions (PSFs) for deconvolution, or using observed PSFs taken at
particular times. Roughly speaking, the secondary has been maintained close
to the same position since July 1990, when the best focus, as described
above, was achieved. There have been significant departures from this mean,
however, and this article contains sufficient information to reconstruct
the focus to an accuracy of about 5 microns for the vast majority of
observations.

There have been a total of 213 mirror adjustments since launch, mostly for
engineering purposes. A complete listing of all the moves applied is
available on STEIS. All 13 mirror moves that have directly affected
scientific observations are described in the first table (p. 8), along with
the date and time of the move and the readouts from the six encoders on the
OTA secondary mirror actuators (relative to an arbitrary zero at launch).
The actuators position the secondary mirror with all six degrees of rigid
body freedom.

The last six columns in the table give the relative secondary mirror
position in physical units (microns of translation and arcseconds of tilt).
These do not include the effects of desorption which are estimated from the
results of a specific focus test. Also given in the table are values for
the position of the secondary at launch, the current position, and the
expected position if no further adjustments are made.



Trends in Focus due to OTA Desorption

Results from many focus measurements, corrected for the known secondary
mirror focus adjustments, are given in the second table (this page),
courtesy of Daniel J. Schroeder. These have been fitted to a decaying
exponential. The best fit in a least squares sense is given by ╢ = 63.4
- 115.6 exp(-t/185.5), where ╢ is the change of focus, in microns, since
16 August 1990, and t is the number of days since 24 April 1990 (HST
launch). The figure (bottom right) shows the exponential fit, where the
discontinuities represent the times at which the secondary was moved.

The scatter about the fit (not shown) is comparable to the required
precision of

focus. An extrapolation of the fit suggests that the OTA will have shrunk
by a total of about 63 microns since 16 August 1990 (1990/114), in general
halving every 129 days.



Telescope Collimation

As mentioned in the November 1991 Newsletter,  there is little astigmatism
at the OTA axis but there is some residual coma which we have chosen not to
remove because it is too small to make much difference. We combine this
information with the fitted desorption trend and the mirror move history to
get the position of the secondary mirror relative to that which would give
zero coma and astigmatism and the nominal HST focus setting.

This relative position (in microns), for each of the important mirror
moves, is shown in the third table (p. 10). We can see that at launch, the
secondary was about

0.8 mm too far from the primary to give the current nominal focus (or about
1 mm out for the paraxial focus). Presently there is no evidence for tilt
in the secondary, but we believe it is decentered along -V3 by about 0.1
mm.

We are now about 5-10 microns from the optimal position, if desorption has
continued to follow the fitted exponential decay. We should expect to make
an adjustment of order 10 microns in early April 1992 after the first data
from the Cycle 1 test are obtained.

The table on p. 10 also gives the amount of aberration expected at the
Faint Object F/96 Camera after each of the mirror moves, in a form suitable
for input to the TIM software. These wavefront errors were obtained by ray
tracing to obtain a field-dependent sensitivity matrix, then multiplying
the measured error by this matrix.



Optics Theory

   This section describes formulae that are useful in understanding the HST
images. The conic constant for the primary mirror has been determined both
by metrology on ground-based test equipment and by phase retrieval on
on-orbit images. The result is

K = -e2 = -1.0139 +/- 0.0005. The optical radius of the mirror (i.e., the
distance from the vertex to the center of curvature) was measured before launch
to be

R1 = 11041.7 mm.

The equation for the sag, or deviation from a plane, of the surface at any
radius r from the vertex is given by:

z(r) = (r2 / R1) /{1 + [ 1 - (1+K) r2 / R12 ]1/2}.

The surface error at the edge of the mirror due to the conic constant error
-that is, the difference between the sag computed from the nominal conic
constant and the sag computed from the measured conic constant - is 2.23
microns. We can compute the induced wavefront error approximately by
doubling this number. It is straightforward to show that the induced
wavefront error is proportional to r4, where r is a normalized pupil
coordinate for an annular aperture (see below), and so corresponds to
spherical aberration.

It is conventional and convenient to express aberrations of an optical
system by expanding the wavefront as a sum of orthonormal polynomials of
rectilinear coordinates in the aperture. This is equivalent to a power
series expansion. For an annular aperture, these polynomials are known as
Zernike polynomials, and the coefficient of each corresponds to a unique
and identifiable aberration.

If r is a normalized pupil coordinate equal to 1 at the edge of the pupil,
the Zernike polynomial coefficient for spherical aberration, Z11, can be
obtained by dividing the wavefront at the edge of the pupil by the
coefficient of r4 in the Zernike polynomial (which is 16.8959 for a central
obscuration ratio of 0.33). This implies Z11= 0.2640 microns rms spherical
aberration. A more careful calculation makes use of the empirical rule that
Z11 = (K + 1.0022985) X 35.3 X 0.6328 = -0.259154, which has been derived
by several groups from a detailed raytrace of the telescope and of the test
equipment, including the effects of higher order spherical aberration.

Many quantities of interest can now be calculated. The longitudinal
spherical aberration is LSA = Z11 X 16.896 X F2 X 16/1000 = 40.225 mm,
where F @ 24 is the OTA image space focal ratio. The transverse spherical
aberration in arcseconds can be computed by dividing by F and multiplying
by the plate scale, and comes out as 6.022 arcsec/mm independent of the
image space.

To compute the focus term in the wavefront at any point, the focus term at
the paraxial focus must first be computed. At the paraxial focus, the
wavefront error is proportional to r4, so the r2 term in the orthogonal
expansion of spherical aberration must be canceled by the r2 term from the
focus polynomial with coefficient Z4. By referring to a table of the
Zernike polynomials (given in the OTA handbook) we can obtain Z4 (paraxial)
= Z11 X 16.896 X 1.1089 / 3.887443 = 1.2490 microns.

To get the focus setting at 12.2 mm from the paraxial focus (where the
encircled energy is maximized according to simulations) we need to subtract
the corresponding focus shift term. This can be shown by geometric
arguments to give a wavefront error at the edge of the pupil equal to the
shift divided by 8 F2. In other words Z4(best) = Z4(paraxial) - 12.2 X
1000/(3.887 X 8 X F2) = 0.5658 microns. This is the focus error in waves
that we aim for. These calculations and the desorption calculations are
applied to an example in the last figure (p. 11).

-Chris Burrows



SCIENCE INSTRUMENTS

FOS Flat Fields

The G190H and G160L gratings of red side of the Faint Object Spectrograph
have lost sensitivity in a wavelength-dependent manner. The blue side and
the other red-side gratings show no such wavelength-dependent sensitivity.

The sensitivity of the G190H and the G160L gratings is affected from about
1800 ANGSTROMS to about 2100 ANGSTROMS, with the greatest decrease at about
1900 ANGSTROMS.  The figure above shows the count rate in G190H as a
function of wavelength for 3 epochs: 27 October 1990, 2 January 1992, and
26 January 1992. A significant change can be seen between October 1990 and
January 1992 (with a maximum difference of about 15%), while a much smaller
change can be seen between the January 2 and January 26 flat fields.

The January observations are part of a monitoring program to provide flat
fields for the red side G190H on a monthly basis. The flat fields produced
from these observations will be placed into the Calibration Data Base
System with a notation about the observation date before which each flat
field should not be used.  Observers can then run the STSDAS package
getrefile to find the appropriate flat field files for calibrating science
data according to the date of observation.  (Note that getrefile is
currently available only in the version of STSDAS installed at STScI.)

-Anne Kinney

GHRS UPDATE

As detailed in the November 1991 Newsletter the GHRS suffered a major
component failure in August 1991. The intermittent power supply on Side 1
not only made any attempt at science operations with Side 1 inadvisable,
but also led to problems using Side 2 since all communications to and from
the instrument currently require some standby power on Side 1.

The nature of the intermittent failure was investigated during November and
December 1991 with an engineering test designed to check the status of the
Science Data Formatter (SDF), the one Side 1 component that is required to
function in order to use Side 2.

Prior to this test, the hypothesis (noted in the November 1991 Newsletter
article) was that tighter control of the Side 1 electronics box temperature
might allow continuous operation of the SDF on Side 1. Keeping the
temperature fluctuations 10í C lower by keeping the Side 2 low voltage on,
and thus increasing the minimum Side 1 electronics temperature to +5í C
instead of -5í C, has been associated with a period of no intermittent
failures since early November 1991.

The engineering test checked the SDF status about once every 5 minutes,
meaning about 10,000 individual queries of the interface, all of which were
successful after the thermal control was put in place.

Given the success of modifying the operational environment, two important
decisions followed. First, it was decided that switching the whole HST
observatory to its redundant Side B electronics in order to allow direct
communication to the Side 2 GHRS SDF was not necessary at the current time.
Second, the GO/GTO community was notified that science operations on Side 2
would be resumed.

Since resumption of Side 2 operations, some 13 GO, GTO, SV and Cycle 1 CAL
proposals have been successfully executed without incident. Several ground
system changes for the GHRS were installed at the end of January, including
keeping Side 2 low voltage on for thermal stability, and adding a
soft-safing capability designed to maintain instrument stability. It is
anticipated that full routine use of GHRS for science observations with
Side 2 will be restored by mid-March 1992.

One of the recent GHRS observations was a sensitivity monitoring
experiment. Compared to results obtained almost exactly one year ago there
is no evidence for any loss of sensitivity over the 1200- 3000 ANGSTROMS
range sampled. Indeed, the formal result is a sensitivity improvement of a
few percent (but consistent with no change).

-Ron Gilliland

WF/PC UPDATE

Calibration Reference Files

The WF/PC Investigation Definition Team (IDT) has delivered most of the
Science Verification (SV) calibration files during the past several months.
Most HST data can be improved by re-calibration using the STSDAS calwfp
task together with these updated calibration files.

Most of the SV program flats (see the November 1991 Newsletter for a list)
are now complete. Flat-field observations for the remaining filter-camera
combinations being used during Cycle 1 are presently being obtained.

To help observers locate the best calibration files for the re- calibration
of their data, a memo entitled wfpc_reference_files has been placed in the
instrument_news section on STEIS. This memo will be updated as new
calibration files are added to the Calibration Data Base.

    Observers should be aware that there are significant residual problems
with the flat-field calibration files. Observations of the sunlit earth
with broad-band filters usually saturate the detectors. The SV program
included broad-band observations of the sunlit earth with a neutral density
filter in the beam (either F8ND or F122M' s red leak) and in some cases,
observations of the earth' s terminator. The neutral density filters have
features that are difficult to remove completely in processing the flats.
Consequently, flat-field calibration files have been assembled for both
types of observations.

It is suggested that observers calibrate their data with both types of flat
fields and compare the results. In all cases observers should examine the
flat fields for strong features coincident with the sources of interest in
their data.



Point Spread Function Calibrations

    The WF/PC PSF has been monitored since mid-1991 in F555W and F785LP
mainly at the center of P6. A number of other positions and filters have
also been observed. These data are being assembled and should be available
in the Calibration Data Base by April 1992. A memo listing the contents of
this database will be maintained on STEIS in the instrument_news section.

The OTA has apparently outgassed to the extent that the WF/PC PSFs have
been stable since around October 1991. The OTA collimation has been decided
and therefore no additional mirror alignment moves are expected (see
article on p. 8). As a result, the WF/PC PSF calibration program will be
modified this spring to concentrate on position and wavelength rather than
temporal variations.



Changes in the Calibration Pipeline

The STSDAS task stsdas.wfpc.calwfp is an exact replica of the calibration
code used in the PODPS (Post Operation Data Processing System) pipeline.
Several new features have been added to this software in recent months.

*  As of 10 February 1992, two new keywords (BIASODD and BIASEVEN) have
been added to the image headers. These are determined from the line
overscan data in the extracted engineering data file (*.x0h) which
accompanies each observation.
The╩pipeline╩bias╩level╩correction (BLEVCORR) now uses the
values of these keywords (rather than the value of the keyword DEZERO) to
subtract the global bias level. The other structure in the bias is still
removed by the subtraction of a bias image (BIASCORR) reference file. The
old version of calwfp remains available in the STSDAS package. Users must
be certain that they have the appropriate bias image reference file (*.r2h)
for the version of the pipeline software they are running. This change was
instituted because of shifts in the odd/even column pattern in the bias
after safing events.

* More keyword values are now being copied into the archival database
that is accessible with STARCAT. These include the " group"  parameters
which are specific to each CCD detector.

-John W. MacKenty



NEWS FOR OBSERVERS AND PROPOSERS

QSO KEY PROJECT REDUCED DATA TO BE AVAILABLE

The Key Project for Quasar Absorption Lines, which involves investigators
John Bahcall, W. L. Sargent, R. J. Weymann,

J. Bergeron, A. Boksenberg, G. Hartig,

B. T. Jannuzi, B. D. Savage, D. P. Schneider, D. Turnshek, and A. M. Wolfe,
has decided to make available to all interested astronomers reduced and
calibrated data from the survey as soon as papers using those data have
been accepted for publication.

As a result, individual astronomers interested in using the data for
various scientific purposes will not have to repeat the tedious reduction
processes involved in correcting the raw data for the instrumental response
or combining the spectra taking proper account of the deflections caused by
the earth' s magnetic field.

The QSO Key Project Team intends to submit for publication papers with the
first statistical analyses of the survey in time for preprints to be of use
to other Cycle 3 observers.  The reduced data will be archived at the STScI
and made available via the Data Systems Operations Branch (contact Mario
Livio, 410-338-4439, userid MLIVIO).

-John Bahcall

STATUS OF THE HST ARCHIVE

All HST data have been archived. Presently the archive contains about 400
Gbytes of data which are archived on 200 pairs of optical disks. Roughly 20
new pairs of disks are generated each month (see diagram on this page).
FITS tapes are generated and distributed regularly to observers (see
diagram on this page).

More than half the data is public (non-proprietary) at present, providing
excellent opportunities for archival research. A complete copy of the data
has been supplied to the Space Telescope European Coordinating Facility
(ST-ECF).

    Some of the old data contain errors and omissions, caused in part by
problems or inadequacies with the archiving software. In order to correct
errors in the archive and the catalogue, a major reprocessing effort will
start soon. Data acquired from

1 January╩1991╩to╩the╩present╩will╩be reprocessed first,
followed by data

from 1990.

Reprocessing should be completed by the fall of 1992, in time for the
initial load into the new Data Archiving and Distribution System (DADS).
According to the present plan DADS will become fully operational in 1993.

Scientists can request non-proprietary archival HST data by filling out the
form " Request for Copy of HST Observations" . This form is available from
the STScI User Support Branch or can be downloaded from STEIS (file
observer/dsob2.ps). Generally, researchers are reminded to check STEIS
periodically, since new information is posted there regularly.

Scientists who need assistance with the reduction and/or analysis of their
data (or who have any questions about the data) are encouraged to contact
the Science Data Analyst Coordinator, Daniel Golombek (410-338-1082, userid
ANALYSIS). Questions about STSDAS should be directed to the STSDAS hotseat
(410-516-5100, userid HOTSEAT). Questions about the data archive may be
addressed to the archive scientist, Stefi Baum (410-338-4797, userid SBAUM)
or to the head of the STScI Data Systems Operations Branch (410- 338-4439,
userid MLIVIO).

-Mario Livio

TINY TIM -

A NEW PSF SIMULATOR

Tiny Tim, a portable program for the easy and fast generation of high
quality HST point spread functions, is now available.  It is written and
distributed in C and should compile on most UNIX and VAX VMS computers
without modification. Executables for use on IBM PC compatible 386+387 or
486 computers are also available, and feature a DOS extender with virtual
memory capabilities.

Tiny Tim includes features such as maps of mirror zonal errors and WF/PC
obscuration shifts.  It is available on STEIS in the software/tinytim
directory.

-John Krist

A GUIDE TO THE STScI RESEARCH SUPPORT BRANCH

In addition to helping General Observers (GOs) with proposing, scheduling,
and executing HST observations, the Space Telescope Science Institute can
be a big help in the data analysis phase.

The Research Support Branch (RSB) provides considerable support to GOs
analyzing their HST data. Some of the typical GO questions that RSB can
answer include: How can I extract some science from my data? Where is the
information I need to continue the analysis? Is this right, or do I have to
do something else?

This article describes the services provided by RSB, and the procedures to
follow to take advantage of them.

Science Data Analysts

RSB has a staff of Scientific Data Analysts (SDAs) who help GOs work with
their HST data. They are knowledgeable about the telescope, the data, and
how to work with the data. Each visiting GO is assigned two SDAs, who serve
as the prime contacts during the visit.

The SDAs are experts in IRAF and STSDAS, particularly the
instrument-specific software. Some are also very proficient with IDL,
others with AIPS, DAOPHOT, or VISTA. All know and use both UNIX and VMS.

Because part of each SDA's time is also devoted to help in-house staff with
their research, they are familiar with a wide range of astronomical work.
They know how, for example, to complement HST spectra with IUE spectra, to
browse on-line catalogs, or to register a radio map with an FOC image. In
addition, the SDAs are also responsible for all GO and staff GASP requests,
in particular those necessary for Phase II observing plans and accurate
measurement of target coordinates.

Scheduling RSB Services

When a GO contacts the User Support Branch (USB) to make arrangements for a
visit to STScI, USB notifies RSB. The SDA Coordinator (SDAC) then contacts
the GO to assess her/his needs. This is generally done by phone, but if
not, via e-mail.

The SDA Coordinator needs to ask many questions. Does the GO know
IRAF/STSDAS? Is this the first time the GO will be dealing with HST data?
Are the observations " complicated?"  Are there many observations? What are
the GO' s plans for analysis? Are special PSFs needed? How many
co-investigators will accompany the GO? Does s/he have all the necessary
(and up-to-date) documentation? Did s/he send the Data Release Form? If so,
are the data to be sent to her/his home institution or picked up at STScI?
Does the GO authorize the SDAC and the SDA to work with the data in
advance? (This last question has to be answered in writing, by sending an
e- mail message, a letter, or a fax.)

The Coordinator then assigns one primary SDA plus one backup to help the GO
during the visit. Together the SDAC and SDAs review the analysis plan,
noting any special requirements specified either in the proposal or in a
communication with the GO. They also consult the Instrument Scientists for
any particular recommendations about how to treat the data.

If necessary, documentation is mailed to the GO. If authorized to do so,
the SDAC and SDAs extract the data from the archive and have it on-line and
ready before the GO arrives. All the necessary reference files are also
on-line or easily accessible, as are any other relevant information (like
the jitter data or the Guide Star Acquisition Report, for example). RSB
provides special visitor accounts, tailored to the needs of the GOs, that
can be used on any of the several public workstations at STScI (both UNIX
and VMS are available).

A Typical Visit

Shortly after arriving at STScI and making contact with USB, the GO is
introduced to her/his assigned SDA. The SDA guides the GO, explaining the
computer logistics, the suggested analysis plan, and the software packages
used. The SDA remains in very close contact with the GO during the entire
visit.

The SDA will also indicate, if necessary, whom to consult for specific
questions (e.g., pointing or acquisition problems). Behind the scenes,
another SDA and/or the SDAC are typically also working on this project,
perhaps obtaining finder charts for a difficult field or tracking down
engineering data. In general, there are far too many details for just one
SDA to cover. Please note that HST data are processed through the
calibration pipeline, archived, and written to tape within two days of the
observations. Before this time, they are accessible only in a format that
is difficult to work with.

A typical visit lasts three or four days, after which the GO can return to
her/his home institution with a fairly good knowledge of the data, how it
has been processed, and how to continue the work. When the GO leaves, the
guest account is disabled and its contents deleted. RSB double checks that
the GO has all the data needed. If necessary a final assessment of what
needs to be done next is discussed by the GO with the SDA, and future
visits to continue working with these data or with new data may also be
discussed. Finally, the GO is asked to evaluate the services provided by
USB and RSB.

Take Advantage of RSB

RSB strongly recommends that all GOs visit STScI at least once, preferably
the first time they receive HST data. RSB has the facilities and the
expertise to help. HST data are complicated, and a visit to STScI not only
will speed the learning process, but will greatly enhance the scientific
yield of the data.

If you plan visit STScI, please give at least two weeks advance notice so
that the necessary arrangements can be made. Contact the User Support
Branch (800-544-8125, 410-338-4413, userid USB) or the Research Support
Branch (410-338-1082, userid ANALYSIS).

-Daniel Golombek

STEIS UPDATE

STEIS is an electronic news service at STScI available through anonymous
FTP (File Transfer Protocol). For details about STEIS and how to use it,
see the December 1990 Newsletter or consult the example on page 19.

The Abstract and Exposure Catalogs have been posted to STEIS. Also, the
RPSS software is available in both the proposer/software/RPSS and
software/rpss directories. After the Phase II deadline, the latter copy
will be removed, and any new versions of the software will appear only in
proposer/software/RPSS.

A new library of sample proposals culled from our database has been posted
to proposer/documents/props_library.

As always, proposers are advised to check the daily HST status reports and
the instrument_news directory for recent information. To find out what' s
been posted since you last logged in, always get the new_items file from
the top level directory.

The sample STEIS session (see figure) was from a VAX-VMS environment.
Commands differ on different systems: for example, under UNIX, you' ll see
a prompt for Name, which should be followed with ╘anonymous' . In the
example given, the commands typed by a user named Smith are in bold face
type.

If your local host does not have stsci in its address table, the Internet
address is 130.167.1.2. It is also possible to reach STEIS through SPAN
(using ZEUS, or node number 6624) or Bitnet (using the Princeton FTP
server).

-Peter Reppert

PROPOSAL SCHEDULING

   HST observers may wonder what becomes of their observing programs
between successful submission to STScI via the Remote Proposal Submission
System (RPSS) and receipt of a data tape from the STScI Data Systems
Operations Branch (DSOB). This article describes the intricate
procedures involved in scheduling HST observations.

The scheduling process addresses three broad objectives: to find and
correct problems that would prevent the successful completion of the
science observations, to determine the optimal time to execute the
observations, and to prepare the sequence of commands that will control the
telescope and Scientific Instruments (SIs) during the observations.

The User Support Branch, Science Planning Branch, and Science Planning and
Scheduling Branch at STScI (with support from the Telescope and
Instruments, Engineering Support, and Advanced Planning Systems Branches)
are all involved in preparing an observation for execution by the HST
observatory.

To do all the work necessary to achieve these objectives generally takes at
least 18 weeks from receipt of a proposal until execution of the first
observations, although both longer and shorter work intervals do occur. If
problems are found that require the proposal to be revised, then the
scheduling duration will be even longer.

The experience at STScI has been that approximately half of the Phase II
proposals do contain problems that must be corrected before they can be
scheduled. Furthermore, the software subsystems are written to operate on
complete proposals, so it is necessary to correct all errors in a proposal
before any of the exposures can be scheduled. Of course, not all the
proposals can be executed right after the Phase II deadline, so some will
be executed at the end of that Cycle, roughly 16 months later.

The Eighteen Week Timeline

Three weeks are used by the User Support Branch for receipt processing.
During that time the RPSS spacecraft time estimate is compared to the
proposal allocation, observations are checked for science duplication with
other science programs, the use of the SIs (especially for target
acquisition) is reviewed with members of the Telescope and Instruments
Branch, and target coordinates are checked by observers using charts
prepared with GASP by USB.

    The observing program is then handed off to the Science Planning Branch
(SPB), which requires five weeks to perform long-range planning for the
observation. The proposal is reformatted by the Transformation subsystem
for use in the planning, scheduling, and commanding systems. Long-range
guide star availability checks are made with the Guide Star Selection
System (GSSS), which is especially important for observations to be made
with fine-lock guiding mode. The SI field of view is searched for bright
objects that might damage detectors. For moving targets, the target aspect
conditions are converted to time windows and the long-range ephemeris of
the target is computed with the Moving Object Support System. Finally, the
best week of the year is selected for each observation using the Spike
subsystem.

The selected weeks are then published on STEIS in the long_range_plan
sub-directory of the observer directory, and the program is delivered to
the Science Planning and Scheduling (SPSS) Branch. The scheduling format is
checked by SPSS for compatability with the most recent requirements, and
the program is test- scheduled to verify consistency with the scheduling
system. Observations from approximately a dozen programs are then placed
into a weekly observing sequence to form a Science Mission Specification
(SMS), following selections and priorities given by SPB. During the
preparation of the SMS, guide stars are selected, the command sequences are
specified, and a final review is performed. All these activities by SPSS
require six and a half weeks. A summary of the SMS is then published on
STEIS in the weekly_timeline directory.

The next two and a half weeks are used by the Mission Operations Center at
Goddard Space Flight Center to determine when the spacecraft tape recorders
are to be read to the ground, to obtain Tracking and Data Relay Satellite
contacts for real-time observations and for tape recorder readouts, to
prepare the commands that point the communications antennas and the solar
arrays, to verify the complete command sequence and command values, and to
prepare the bit stream to be sent to HST. This work is completed one week
before the observations on a weekly SMS begin execution, and the command
loads are generated five days prior to SMS execution.

Observer Input

Observers may be involved in the scheduling process in several ways. They
receive a set of finding charts for their observations which they should
check to verify that correct coordinates have been provided. Targets may
have to be removed if bright, damaging sources are found in the SI field of
view. Observers can use STEIS to check the observation schedule.

Observing programs may have to be modified, with different exposure times
or observing sequence specifications (such as SEQ NON-INT, or SPATIAL
SCAN), in order to make it possible to schedule some observations. The need
for such changes is identified during the operation of the Transformation,
Spike, and SPSS subsystems. These software subsystems are used to compute
the total elapsed time necessary to execute each sequence of observations
and to compute the duration of available target visibility windows. They
are also used to verify the logical consistency of observer-specified
linkages and their compatibility with external constraints such as the
duration of target visibility windows, solar avoidance, and spacecraft
dark-time and South Atlantic Anomaly passage. These checks by STScI often
reveal problems that an observer could not easily have found.

While the kinds of problems described above may require consultation with
observers to effect solutions, other scheduling problems may be solved here
at STScI. For example, some exposures are too long to be completed during
orbital target visibility. If trimming the exposure duration will make it
possible to schedule the observation, then STScI will do that. As stated in
the Proposal Instructions, the observation will be trimmed as necessary,
but so that the signal-to-noise ratio is not decreased by more than 25%.

   We hope that this description has provided insight into the present
process of scheduling observations for HST. The process can be improved,
and we are investigating ways to decrease the work required of STScI and of
observers to prepare observations for execution. A task force chaired by
Jim Etchison and Peg Stanley was established in January 1992 (see p. 6) to
investigate this issue and to recommend ways to increase scheduling
efficiency by improving the end-to-end proposal processing procedures.

-Larry Petro & Jim Etchison



PROPOSAL NEWS

CYCLE 2 PROPOSAL REVIEW AND SELECTION

    The selection of HST Cycle 2 observing programs has been completed. The
statistics of received proposals were presented in the November 1991
Newsletter (p. 19). As shown there, four kinds of proposals were
considered: standard General Observer, Guaranteed Time Observer
Augmentation (see the June 1991 Newsletter, p. 12, for a description of the
associated policy), Snapshot (March 1991 Newsletter, p. 8), and Archival
Research. All four types of proposals were reviewed comparatively for
scientific merit by the same committees, although the resources involved are
distinct (with the exception of the US GO/AR funding).

Proposals were mailed well in advance of the panel meetings to members of
the appropriate subdiscipline panel. Each proposal was assigned one primary
and two secondary reviewers. Preliminary grades were assigned by the
designated reviewers prior to the meetings, and these helped define the
order of discussion within scientific subcategories.

   During the panel meetings, each proposal was presented by the three
assigned reviewers and discussed by the full panel (excluding anyone with
institutional or competitive conflicts). The panel then made resource
recommendations and voted on a final grade. After all the proposals were
graded, the panel generated a ranked list.

The reviewers also prepared written comments describing their rationale and
any specific recommendations for transmission to the proposers. These
comments were usually comprehensive and useful, although the large volume
of proposals occasionally led to excessively brief written comments. Any
perfunctory comments should not be construed by the proposers to mirror the
review process itself.

The Solar System panel met at the STScI during 4-6 December 1991. All other
subdiscipline panels met concurrently during 9-11 December, and the
cross-discipline Telescope╩Allocation╩Committee (TAC) met 12-13
December to integrate and reconcile the individual panel recommendations.

The TAC consisted of its chair, the six panel chairs, and six additional
members-at-large who did not participate in the subdiscipline panels. The
latter individuals provided broader perspectives to counterbalance the
natural and desirable advocacy by the panel chairs.

A total of sixty-four astronomers contributed their valuable time and
expertise to this extensive review effort (the complete membership of the
panels and TAC is listed in the table on p. 21).

The TAC recommendations were reviewed by the STScI Director, or in the case
of the GTO Augmentations by the NASA HST Program Scientist, during the week
following the peer meetings. They made final decisions on a few remaining
issues during the first week of January 1992, and notifications to all
proposers were mailed on January 15.

The complete list of approved Cycle 2 GO/AR programs and general
statistical results of the review are given in tables on pp. 22-26. The
article following this one describes the procedures and timeline for the
Phase II activities.

    The determination of the appropriate subdiscipline balance during the
TAC meeting proved more difficult than in Cycle 1. (The Cycle 1 balance both
before and after the Reassessment TAC review can be found on p. 18 of the
June 1991 Newsletter.) Following suggestions by the peer reviewers and
discussion within the STScI, several procedural refinements to facilitate
the integration of the panel and TAC roles in future cycles are under
consideration.

The possibilities include a meeting of the full TAC at the end of the first
day of panel meetings, to consider the Large/Key program recommendations
and arrive at a preliminary subdiscipline balance which the panels can
adopt as specific targets during their remaining deliberations and
rankings. It may also be desirable to include two members from each panel
on the TAC. Finally, the topical composition of the two stellar panels will
be redefined in an attempt to achieve a more even distribution of proposal
volume, since Stellar Astrophysics received a larger number than any other
panel in both Cycles 1 and 2.

The heavy oversubscription of HST entails an inevitable measure of
frustration for reviewers and proposers alike; many meritorious proposals
could not be accommodated. The available time is determined by the typical
spacecraft efficiency of 30%, or 2630 hours annually. Thirty percent of
that amount is consumed by overheads (15% calibration/engineering, 10%
repeats, 5% Director' s Discretionary time). Of the balance, 30% on
average, or 550 hours, is designated for the GTO program, leaving
approximately 1300 hours of GO spacecraft time per cycle.

The possibilities of increasing the available time through scheduling
enhancements such as greater use of the Continuous Viewing Zones, and of
improving the exposure-time efficiency for a given spacecraft time, are
currently being investigated by the STScI (see p. 6). In any case, this
very oversubscription, together with the extensive efforts of both the peer
reviewers and STScI staff, guarantees that an outstanding scientific
program has been selected for Cycle 2 of HST.

-Nolan Walborn

CYCLE 2 SCIENCE PROGRAMS AND CYCLE 3 PROPOSALS

    Selection notification letters were sent to Cycle 2 proposers on 15
January 1992, and Phase II instructions were sent to PIs of all approved
observing programs. Phase II is when the accepted Phase I proposals are
transformed into detailed computer-readable files containing the
information needed for scheduling and implementation of the observations.
The Phase II deadline for approved Cycle 2 programs was 20 March 1992; for
approved future- cycle programs it is 24 April 1992.

HST is an inherently complicated observatory to use, and the STScI is
continuing to develop ways to lessen the workload for users. We provide a
considerable array of support and information for Phase II, much of which
has been newly developed or recently updated based on our experience since
launch.  Listed below are some of the more significant changes:

*  Phase II Proposal Instructions have been updated, including new
instructions on Target Descriptions, a section describing parallel
observations, and new guiding tolerances.

*  Target Acquisition Handbooks have been updated, with revisions that
reflect in-orbit experience and new techniques.

*  RPSS software, available through STEIS, has been updated to conform
with the new proposal instructions, and the Resource Estimator has been
adjusted to provide better estimates of spacecraft time.

*  A library of sample Phase II programs has been posted on STEIS to
serve as examples and templates for Cycle 2 submissions.  These programs
are derived from those that have successfully executed on HST, and utilize
common  modes for the various scientific instruments.

*  The GNUPEP editor, which is an optional program editor, has been
created as an alternative to the RPSS template editor.  It can be
downloaded from STEIS, and provides those who can work in the GNU Emacs
environment with more on-line assistance when creating and editing the
program files.

*  Preliminary Exposure and Abstract Catalogs for the accepted Cycle 2
programs have been posted on STEIS.

   Many users are new to HST this cycle, and the time available to create
the Phase II programs is short. It is often fast and effective for users to
come to the STScI to work directly with the staff when preparing Phase II
programs.  A limited amount of financial support is available for HST users
at U.S. institutions to visit STScI for this purpose, with priority given
to first-time users. Please contact Sheryl Falgout in the

User Support Branch (410-338-4413, userid FALGOUT) to make the necessary
arrangements.

Cycle 2 observations are expected to begin around July 1992, with some
programs started earlier if possible.  The Call for Proposals for Cycle 3
will be issued around 1 May 1992, with a proposal deadline of mid-August.

-Bruce Gillespie



SOFTWARE NEWS

STSDAS VERSION 1.2 RELEASED

Version 1.2 of the Space Telescope Science Data Analysis Software (STSDAS)
was released on 13 January 1992, and is now the default for most machines
at STScI. Off-site users may obtain this new software by contacting the
STSDAS System Administrator, Ray Williamson (410-516-8400,
[e-mail]), for a distribution tape and installation
instructions. Alternatively, users may obtain STSDAS via anonymous FTP on
STEIS. If you choose to get the software electronically (as many sites do),
please send the electronic registration form to STScI so you can be
notified about revisions to the software and documentation.

Major releases of STSDAS will occur roughly every year and a half, but the
latest updates and bug fixes will also be made available to outside users
in the form of incremental upgrades, or " patch"  kits. These patches will
be prepared as needed, probably every three to four months, and will be
available electronically.

Concurrent with the STSDAS release, STScI has also released V1.2 of the
TABLES external package. This package is intended for sites whose software
(e.g., SAO' s XRAY package) requires the tools utilities, but not the rest
of STSDAS. The TABLES package now also includes the Interactive Graphics
Interpreter task (stplot.igi) and FITS utilities (from the fitsio package).
As with STSDAS, the TABLES package is available on STEIS via anonymous FTP.

-Dick Shaw & Bob Hanisch

NEW FEATURES OF STSDAS

Several new tasks have appeared since the last incremental release of
STSDAS (V1.1D) in June 1991, including two in the new restore package to
deconvolve HST images, and a new task to determine the orbital position of
HST from an ephemeris.

The wfpc package also has several new tasks, including one to compute image
statistics on multi-group images (excluding flagged data), and one to
determine the noise and gain characteristic for each chip.

Tasks in the fourier package have been enhanced to make use of World
Coordinate System information in the image headers, and the calibration
pipeline tasks have also been revised to accommodate several changes to the
FITS-style science data header keywords.

Note that the new HRS and FOS pipelines are incompatible with the old
headers (prior to SOGS Build 28 in November 1991), but utilities are
available to convert the old headers for those instruments to the new
format. See the November 1991 Newsletter for additional details.

Some tasks that were not necessarily written by the STSDAS group, such as
redshift, have been moved into a new package called contrib. As its name
implies, this provides a means for useful, user- contributed software to be
distributed to the community. Please note, however, that while the STSDAS
group will make some effort to ensure that these tasks function without
obvious problems, they can only be supported at a minimal level. The STSDAS
group will report bugs to the contributing authors and install their
revisions, but will not generally fix bugs in these tasks, nor guarantee
that the output is accurate.

Users who would like more details about STSDAS software may wish to receive
our new STSDAS Newsletter, which is prepared two or three times per year.
The STSDAS Newsletter provides many useful insights into using some of the
more complicated tasks, advice on which STSDAS tasks are most appropriate
for particular types of analyses, and descriptions of new tasks that are
being developed. Please contact Mark Stevens (410-516-8154,
[e-mail]) to obtain the first (Fall 1991) and subsequent issues.

-Dick Shaw & Bob Hanisch

NEW/UPDATED DOCUMENTATION AVAILABLE

With the release of STSDAS V1.2, the user manuals have been substantially
revised and updated. These include the STSDAS User' s Guide, STSDAS
Calibration Guide, Site Manager' s Guide, STSDAS Installation Procedures
and, for local users and visitors, the STScI Site Guide for STSDAS and
IRAF. Three new Quick Reference Cards are also available: one each for IRAF
and STSDAS, CL programming, and site management.

All of these documents are available from the STSDAS Group, and full sets
will be mailed to sites from which we receive either distribution requests
or electronic registration forms. These guides are also distributed in
electronic form with the STSDAS source code, and can be found in
sub-directories of stsdas$doc/user in both PostScript and ASCII-text files.

-Dick Shaw & Bob Hanisch

IRAF UPGRADES

The new release of IRAF V2.10 should be available to users on SUN systems
by the time this Newsletter is distributed. We received the BETA release of
V2.10 for testing against STSDAS V1.2; users should find that STSDAS V1.2
works well with either IRAF V2.9.3 or IRAF V2.10.

The V2.10 BETA version has been installed on some of the STScI SUN clusters
and is available as irafx, or the development version of IRAF. This was
necessitated by the demand for the improved tape drive interface in V2.10,
which supports newer devices such as Exabytes and DATs.

The new version of IRAF will also feature a new networking driver, which
will be faster and more reliable, and will eliminate the bothersome
multiple password prompts when accessing data on different machines.

The V2.10 release for VAX systems will probably not be available for
another six months or so, but it will be installed for visitor and local
use as soon as possible.

-Dick Shaw & Bob Hanisch



INSTITUTE NEWS

DIGITIZED SKY SURVEYS ON CD ROM

The STScI recently surveyed the astronomical community to determine
interest in acquiring the digitized sky surveys (DSS) on CD ROM. The
response has been overwhelmingly positive.  This article describes the
status of the distribution project.

Over 200 astronomical institutions and several dozen individual astronomers
have informed STScI of their desire to acquire the DSS. Most are using Sun
or Dec workstations, with Unix or VMS operating systems.  Many stated that
they could probably afford $2000 for the DSS, but that $6000 would be
difficult to find.

NASA Headquarters recently supported an STScI study to ascertain effective
ways of distributing the DSS.  The study emphasized data- compression
algorithms (to ease greatly the cost and bulk of distributing a 0.6
TeraByte-sized dataset).  A highly efficient algorithm has been identified,
tested extensively, and used to compress the digitized versions of seven of
the Schmidt plates in the Guide Stars Archives. A " sampler"  CD ROM,
containing the compressed, digitized images of these seven plates, has been
produced.

As an example, we show a galaxy image after compression and decompression
(with the H-Transform algorithm) by factors between 1 and 82 in the figure
at left.  The algorithm and details of the tests carried out with it are
described by White, Postman, and Lattanzi (Proceedings of the June 1991
Workshop on Digitized Optical Sky Surveys, Edinburgh, Scotland, in press).
A free copy of the sampler CD ROM, plus software to access the images on
it, is being distributed to every institution that responded to the STScI
survey. A limited number of additional sampler CD ROMS is still available.
These will be mailed free of charge, on a first-come, first-served basis to
institutions requesting them.

Encouraged by the positive community response, NASA Headquarters has now
approved an STScI request to compress the 1477 digitized scans covering the
entire sky.  At a compression factor of ~10X, these compressed scans will
fit on fewer than 100 CD ROMs, and occupy less than 2 linear feet of shelf
space.  NASA is also providing support for a highly compressed (~80X)
version of the DSS, useful for " quick look"  analysis, finder charts, and
educational purposes. The generous support provided by NASA will
significantly reduce the cost to the astronomical community.

The southern sky survey (Science and Engineering Research Council J plates)
will be compressed first, followed by the northern sky Palomar Observatory
103a-E survey.  A precise timetable is difficult to establish, but the
digitized southern sky should be available in two years; the northern sky
will follow one year later. The availability, cost, and details of ordering
the DSS will be well publicized, with sufficient lead time to enable
institutions to budget for it.

The STScI appreciates the strong support from the community on this
project, and we look forward to the opportunity to provide the full DSS in
the near future.

-Michael Shara

HUBBLE FELLOWSHIP PROGRAM

The 115 applications received for the third round of Hubble Fellowships
were considered by the Review Panel in late January 1992. Offers to
successful candidates have been made, with replies due by mid-February
1992.

The selection process should be completed by early March 1992 at which time
the names of this year' s new Hubble Fellows will be announced.

An Announcement of Opportunity for the third round of Hubble Fellowships
will be issued in early Summer 1992.  The deadline for submitting
applications is anticipated to be mid-November 1992.

-Nino Panagia

PASP NEWS

As described in the June 1991 Newsletter, the editorial office of the
Publications of the Astronomical Society of the Pacific (PASP) is now
located at STScI.  The editorial staff at STScI consists of Howard E. Bond
(Managing Editor), Abhijit Saha (Deputy Editor), and Denise Dankert
(Editorial Assistant).

Starting with the January 1992 issue, PASP has been published by the
American Institute of Physics.  The journal has been redesigned, with a new
cover that now carries a different illustration each month.

We believe that PASP has the fastest publication schedule of any of the
major astronomical journals (2.5 months from acceptance of the last
manuscript for an issue until that issue is printed and mailed).

PASP continues to welcome submissions in all areas of astronomy and
astrophysics including, of course, papers reporting HST results.

-Howard E. Bond

ANNUAL STScI MAY SYMPOSIUM

The topic of the STScI Symposium this year is Astrophysical Jets. The
Symposium will be held at the Institute on 12-14 May 1992. The purpose of
the Symposium is to consider physical processes that operate in both
stellar and extragalactic jets, and whether an understanding of one
contributes to an understanding of the other.

Invited reviews will be presented by Jim Pringle, Roger Blandford, Bo
Reipurth, Alan Marscher, Sterl Phinney, Robert Laing, Andrew Wilson, Tom
Ray, Steve Stahler,Michael╩Norman,Rene Vermeulen, John Biretta, and
Mitch Begelman. Shorter contributions will be in the form of posters. As
with other STScI Symposia, the proceedings will be published by Cambridge
University Press.

The deadline for registration was April 1992. Barbara Jedrzejewski, STScI
Workshop Coordinator (410-338-4836, fax [phone], userid ELLER).

-Mike Fall

HST WORKSHOP IN SARDINIA

    Preparations are well under way for the forthcoming workshop on "
Science with the Hubble Space Telescope"  to be held in Sardinia during 29
June through 7

July 1992.

There appears to be great interest in this meeting, and we expect many new
HST results to be presented. The deadline for abstracts, registration, and
deposits was 31 March.

-Ethan Schreier

NEW DATES FOR WORKSHOP ON WOMEN IN ASTRONOMY

    The last issue of the Newsletter described the meeting " Women at Work:
the Status of Women in Astronomy"  that will be held at STScI in the fall
of 1992. The correct dates for the meeting are 8-9 September, not 3-4
September as previously published.

The workshop will be geared toward graduate students, postdocs, junior and
senior astronomers, administrators, and representatives of funding
agencies. The agenda will include discussion of the current status of women
in the field, the particular challenges women face, and ways to improve the
recruitment and retention of women in astronomy.

The organizing committee for the workshop includes Neta Bahcall, Peter
Boyce, France Cùrdova, Laura Danly, Doug Duncan, Riccardo Giacconi,
Anne Kinney, Julie Lutz, Goetz Oertel, Charles Pellerin, Ethan Schreier,
Meg Urry, and Sidney Wolff.

A poster advertizing the workshop will soon be sent to a wide distribution.
If you have not received a poster by the end of April, and you are
interested in receiving further details about the workshop, please contact
Barbara Jedrzejewski, Conference Coordinator (410-338-4836,userid ELLER)

-Meg Urry

ESA FELLOWSHIPS AT STScI

Astronomers of the European Space Agency (ESA) member countries are
reminded of the possibility of coming to STScI as ESA Fellows. Prospective
fellowship candidates should aim to work with a particular member or
members of the ESA staff at STScI, and for this reason applications must be
accompanied by a supporting letter from STScI.

Details of the interests of staff members at STScI can be obtained from Dr.
Nino Panagia in the Academic Affairs Division (410-338- 4916, userid
PANAGIA). Details of the fellowships and applications procedures can be
obtained from the Education Office, ESA, 8-10 rue Mario Nikis, 75738 Paris
15, France. Completed application forms must be submitted through the
appropriate national authority and should reach ESA no later than 31 March
for consideration in May, and no later than September 30 for consideration
in November.

-Nino Panagia

STAFF NEWS

Phil Martell became a postdoc at STScI in April 1991 after completing his
Ph.D. thesis on intermediate polars at the Ohio State University. Phil is
currently making stroboscopic Doppler maps of these asynchronously-rotating
magnetic cataclysmic variables.

Fuhua Cheng joined STScI as a postdoc in August 1991. Previously he was at
the University of California at Santa Cruz, where he developed models of
accretion disk spectra and polarization. Fuhua has recently been
interpreting HST observations of Nova Muscae 1991.

In December Todd Henry joined STScI as a post-doc, having completed his
thesis at the University of Arizona on infrared speckle imaging of nearby M
dwarfs in a search for sub-stellar companions. He will be working with Dave
Soderblom on target selection for NASA's SETI Microwave Observing Project.

     Carole Haswell became a postdoc at STScI in February 1992, after
completing her Ph.D. thesis on the black-hole binary A0620-00 at the
University of Texas at Austin.

Ron Downes has joined the User Support Branch as a Proposal Scientist. He
comes to STScI from the the ROSAT Data Center at Goddard. Prior to that, he
spent 6 years working with the FOS team. Ron' s main area of research
interest is cataclysmic variables.

Keith Noll has joined STScI as a Planning Scientist in the Science Planning
Branch. Most recently, he was a National Research Council Fellow at
Marshall Space Flight Center, where he went after completing his Ph.D.
thesis at the State University of New York at Stony Brook. His research
specialty is the solar system, particularly infrared spectroscopy of the
outer planets.

Alex Storrs comes to STScI from a postdoctoral position at McDonald
Observatory where he studied cometary continua in spectra in the Faint
Comet Survey. Alex has joined the Science Planning Branch as a Planning
Scientist. His research interests lie generally in the direction of the
formation of planetary systems, and specifically in the composition of
comets.

There have been several new appointments in the Telescope and Instruments
Branch (TIB). Having completed his sabbatical, David Soderblom has returned
to programmatic work as a GHRS Instrument Scientist. Dave replaces Doug
Duncan who began his own sabbatical in January.                Steve
Hulbert has accepted a position as Assistant Scientist in TIB and will also
work on the GHRS, primarily analyzing calibration data. Charles (Tony)
Keyes joined the FOS group as an Assistant Scientist, and will have
responsibilities for calibration. Bill Sparks, formerly FOC Instrument
Scientist, is now a WF/PC instrument scientist. Except for Bill, these new
TIB staff worked previously in other areas of the Institute, and their
experience will add to the depth of talent in the spectroscopic group.

     Brad Whitmore began a sabbatical in January. His research interests
include the study of stellar velocity dispersions, polar ring galaxies,
clusters of galaxies, and interacting/merging galaxies. Brad has served as
Deputy Division Head of the Science Programs Division for the past four years.

Chris Blades has accepted the position of Deputy Division Head in the
Science Programs Division. He served as Chief of the Telescope and
Instruments Branch for nearly four years prior to this step up to the
Division Office. Chris' s main research interests are concerned with
studies of the interstellar medium, especially galactic halo studies and
gas in external galaxies.

     Andrew Wilson has moved north from the University of Maryland to join
the Academic Affairs Branch at STScI. Andrew is well-known for his research
on active galaxies, particularly Seyferts, in a variety of wavebands.

In June Meg Urry will become Chief of the Research Support Branch. At
present she works in the Science Program Selection Office where, among
other things, she edits the STScI Newsletter. Meg' s research involves
multiwavelength spectral and variability studies of active galaxies.



RECENT STScI PREPRINTS

586.  " White Dwarf Masses in Nova Systems and the Maximum- Magnitude vs.
Rate-of-Decline Relation"  and " The Cyclic Evolution- ╘Hibernation'
Scenario of Cataclysmic Variables,"  M. Livio.

587.  " RR Lyrae Stars in Local Group Galaxies III. NGC 205,"  A. Saha,
J.G. Hoessel, J. Krist.

588.  " Spiral Instabilities and Bars in N-Body Simulations,"  J.A.
Sellwood.

589.  " Why Do all the Extragalactic Jets Have Lorentz Factors less than
Twenty?"  M.A. Abramowicz.

590.  " HST Observations of Jets and AGNs,"  F. Macchetto.

591.  " Dynamics of Ultraharmonic Resonances,"  P. Artymowicz, S.H. Lubow.

592.  " Spectroscopy of Emission Line Nebulae in Powerful Radio Galaxies:
Interpretation,"  S.A. Baum, T.M. Heckman, W. van Breugel.

593.  " The First Year of Observations with the Hubble Space Telescope,"
A.L. Kinney, S.P. Maran.

594. " Flexures of Conventional Cassegrain-Fed Spectrographs,"  U. Munari,
M.G. Lattanzi.

595.  " The AGK3U: An Updated Version of the AGK3,"  B. Bucciarelli, D.
Daou, M.G. Lattanzi, L.G. Taff.

596.  " A Search for Gravitational Lenses Using Sky Survey Plate Scans,"
G. Meylan, S. Djorgovski, J. Surdej, B. Pirenne,  W.N. Weir, S. Beaulieu; "
A Search for the Optical Counterpart of the Einstein Ring PKS 1830-211,"
S. Djorgovski, G. Meylan, D. Thompson,

N. Weir, G. Swarup, P. Rao, R. Subrahmanyan, A. Smette.

597.  " Type 1 Supernovae and Accretion Induced Collapses from Cataclysmic
Variables?"  M. Livio, J.W. Truran.

598.  " Optimal Grazing Incidence Optics, and its Application to Wide Field
X-Ray Imaging,"  C.J. Burrows, R. Burg, R. Giacconi.

599.  " The Implications of Runaway OB Stars for High Mass Star Formation,"
 C.J. Clarke, J.E. Pringle.

600.  " A New Class of Galactic Discrete g-ray Sources: Chaotic Winds of
Massive Stars,"  " Low Energy g-ray Emission from the Cygnus OB2
Association,"  W. Chen, R.L. White.

601.  " The Common Envelope Phase in Novae,"  M. Livio.

602.  " AG Carinae and the LBV Phenomenon,"  C. Leitherer, A.D. Neto, W.
Schmutz.

603.  " Classical Novae and the Extragalactic Distance Scale,"  M. Livio.

604.  " The Infrared Properties of Quasars and Radio Galaxies: Testing the
Unification Schemes,"  T.M. Heckman, K.C. Chambers, M. Postman.

605.  " Circumstellar Discs,"  J.E. Pringle.

606.  " Catalog-to-Catalog Reductions: Results for the FK Catalogs, the N30
and the GC,"  L.G. Taff, B. Bucciarelli, M.G. Lattanzi.

607.  " Target Selection Strategy for NASA' s SETI/MOP,"  D.R. Soderblom,
D.W. Latham.

608.  " Emission Line Nebulae in Clusters of Galaxies,"  S.A. Baum.

609.  " Non-Thermal Emissions from Hot Stars,"  R.L. White, W. Chen.

610.  " Ultraviolet and Radio Observations of Milky Way Halo Gas,"  L.
Danly, F.J. Lockman, M.R. Meade, B.D. Savage.

611.  " On the Kinematics of Intermediate-Redshift Gaseous Galaxy Halos,"
K.M. Lanzetta, D.V. Bowen.

612.  " Detection of a Local High Velocity Absorption Line System Towards
HD 93721,"  B.E. Penprase, J.C. Blades.

613.  " Spin Down of Rapidly Rotating, Convective Stars,"  C.A. Tout, J.E.
Pringle.

614. " Evidence for an Extranuclear AGN Fuel Source,"  T.M. Heckman.

615.  " Electron Temperature Variations and the Measurement of Nebular
Abundances,"  D.R. Garnett.

616.  " The Braided Jets in the Spiral Galaxy NGC 4258,"  G. Cecil, A.S.
Wilson, R.B. Tully.

617.  " p√-Decay Gamma-ray Emission from Winds of Massive Stars," R.L.
White, W. Chen.

618.  " Observation of Circumstellar Environments with the Hubble Space
Telescope,"  F. Paresce.

619.  " Unification of Radio-Loud AGN,"  C.M. Urry, P. Padovani; " Lyman
Edges: Signatures of Accretion Disks,"  A.L. Kinney; " Preliminary Results
of Optical and Near Infrared Imaging of GPS Radio Sources: Evidence for an
Obscured AGN?"  C.P. O' Dea, J.K. Davies, C. Stanghellini, S.A. Baum, E.
Laurikainen; " Time Dependent Inhomogeneous Jet Models for BL Lac Objects,"
 A.T. Marlowe, C.M. Urry, I.M. George.

620.  " The Contribution of Quasars to the Ultraviolet Extragalactic
Background,"  P. Madau.

621.  " On the Role of Radioactive Decays in Powering g-rays and X- rays
from Novae,"  M. Livio, A. Mastichiadis, H. àgelman, J.W. Truran.



HOW TO CONTACT STScI

Telephone: The area code for Baltimore has changed from 301 to 410. The
telephone numbers for staff members are generally of the form 410-338-xxxx,
or in some cases 410-516-xxxx, where xxxx is the extension number. Two
important cases with the 516 extension are the Grants Administration Branch
(410-516-8611) and the SDAS Hot Seat (410-516-5100). If an individual staff
member' s number is not known, call the STScI receptionist at 410-338-4700.

Fax: [phone]

Mail:     STScI

    3700 San Martin Drive

    Baltimore, MD 21218

    USA

E-mail: It is possible to reach most staff members at STScI on NSI/DECnet
(formerly known as SPAN), BITNET, and Internet. Address formats are as
follows:

NSI/DECnet:   stscic::userid

        or 6559::userid

BITNET:    [e-mail]

Internet:    [e-mail]

In most, but not all, cases the " userid"  is the staff member' s surname.
Alternatively, many userids are published in the Membership Directory of
the American Astronomical Society. If you have difficulty reaching someone,
please send the mail to the User Support Branch (userid USB), which will
forward it. The USB is the central point of contact for scientists who wish
to conduct research with HST.



Newsletter Notes

Comments on this issue of the STScI Newsletter should be addressed to the
Editor, Meg Urry (410-338-4593, userid CMU). Mailing-list corrections
should be sent to Amy Connor (userid CONNOR).

Persons who assisted in the preparation of this issue include John Godfrey,
Dave Paradise, and Pete Reppert.

The STScI Newsletter is issued three to four times a year by the Space
Telescope Science Institute, which is operated by the Association of
Universities for Research in Astronomy, Inc., for the National Aeronautics
and Space Administration.