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 observationsÊfor 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 5¡ 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 10¡ C lower by keeping the Side 2 low voltage on, and thus increasing the minimum Side 1 electronics temperature to +5¡ C instead of -5¡ 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. TheÊpipelineÊbiasÊlevelÊcorrection (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 JanuaryÊ1991ÊtoÊtheÊpresentÊwillÊbe 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 Ôanonymous' . 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 TelescopeÊAllocationÊCommittee (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, williamson@stsci.edu), 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, stevens@stsci.edu) 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,MichaelÊNorman,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 410-338-4767, 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 C—rdova, 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- ÔHibernation' 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. " pû-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. …gelman, 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: 410-338-4767 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: userid@stsci.bitnet Internet: userid@stsci.edu 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.