Status Report

NASA Hubble Space Telescope Daily Report # 4613

By SpaceRef Editor
May 19, 2008
Filed under , ,


Continuing to collect World Class Science

PERIOD COVERED: 5am May 16 – 5am May 19, 2008 (DOY 137/0900z-140/0900z)


NIC1/NIC2/NIC3 8795

NICMOS Post-SAA calibration – CR Persistence Part 6

A new procedure proposed to alleviate the CR-persistence problem of NICMOS. Dark frames will be obtained immediately upon exiting the SAA contour 23, and every time a NICMOS exposure is scheduled within 50 minutes of coming out of the SAA. The darks will be obtained in parallel in all three NICMOS Cameras. The POST-SAA darks will be non-standard reference files available to users with a USEAFTER date/time mark. The keyword ‘USEAFTER=3Ddate/time’ will also be added to the header of each POST-SAA DARK frame. The keyword must be populated with the time, in addition to the date, because HST crosses the SAA ~8 times per day so each POST-SAA DARK will need to have the appropriate time specified, for users to identify the ones they need. Both the raw and processed images will be archived as POST-SAA DARKSs. Generally we expect that all NICMOS science/calibration observations started within 50 minutes of leaving an SAA will need such maps to remove the CR persistence from the science i mages. Each observation will need its own CRMAP, as different SAA passages leave different imprints on the NICMOS detectors.

NIC1/NIC2/NIC3 8794

NICMOS Post-SAA calibration – CR Persistence Part 5

A new procedure proposed to alleviate the CR-persistence problem of NICMOS. Dark frames will be obtained immediately upon exiting the SAA contour 23, and every time a NICMOS exposure is scheduled within 50 minutes of coming out of the SAA. The darks will be obtained in parallel in all three NICMOS Cameras. The POST-SAA darks will be non-standard reference files available to users with a USEAFTER date/time mark. The keyword ‘USEAFTER=3Ddate/time’ will also be added to the header of each POST-SAA DARK frame. The keyword must be populated with the time, in addition to the date, because HST crosses the SAA ~8 times per day so each POST-SAA DARK will need to have the appropriate time specified, for users to identify the ones they need. Both the raw and processed images will be archived as POST-SAA DARKs. Generally we expect that all NICMOS science/calibration observations started within 50 minutes of leaving an SAA will need such maps to remove the CR persistence from the science images. Each observation will need its own CRMAP, as different SAA passages leave different imprints on the NICMOS detectors.

WFPC2 11518

Mutual eclipses of a Kuiper belt-satellite system

Ground-based observations two weeks ago strongly suggest that the orbit of the small inner satellite of 2003 EL61, the 5th largest known dwarf planet, is possibly precisely edge-on and thus somewhere in the middle of a ~3 year long cycle of mutual eclipses, occultations, and transits. We anticipate that with another year of ground-based observation we may have sufficient data to accurately predict the times and durations of these events, but by then the events may well be over. If events are indeed occurring, measurement of the timing and depths of such events provides a wealth of precise geometric information for constraining sizes, shapes, orbits, and dynamics of the system.

We propose to obtain 5 quick WFPC2 visits to 2003 EL61 over the ~19 day orbital period of the inner satellite to determine a precise orbit and predict mutual event times. We will instantly (within ~1 day of the end of the observations) make these predictions public to allow the maximum number of attempts to collect the data as possible.

ACS/SBC 11517

A >10000 solar mass black hole

The X-ray source XMMUJ134736.6+173403 has recently been discovered serendipitously. Its X-ray position coincides with two interacting galaxies, one of which is a Seyfert II. The X-ray variability and spectrum rule out an association with the Seyfert II. Carpano et al. (2008) suggest that the source is a foreground quiescent low-mass X-ray binary (unrelated to the galaxy-pair). Our recent optical photometry rules out such a scenario since the counterpart to the low-mass X-ray binary should have been detected. Furthermore, we find an extended source in the XMM error circle. Optical spectroscopy shows emission lines, such as those found in ULX nebulae, redshifted to the same redshift as that of the pair of interacting galaxies. Swift/UVOT observations show that the spectrum of the emission nebula is very blue. If this emission nebula is indeed associated with the X-ray source it implies that the X-ray source is a ULX. We propose here to obtain an ACS/SBC image to accurately determine the magnitude and the extend of the nebula and to investigate if the ULX/nebula emission can be responsible for the observed X-ray emission by extending the SED to ~1300 angstrom.

WFPC2 11498

2008 Passage of Jupiter’s Great Red Spot and Oval BA

Jupiter’s largest anticyclonic storm, the Great Red Spot (GRS), drifts slowly westward relative to the radio rotation rate of the planet (System III W. longitude). In contrast, the next largest storm, Oval BA (a.k.a. the Little Red Spot or LRS), drifts slowly eastward. The relative drift of the two is approximately 0.5 deg/day, resulting in a passage of the storms every two years. The GRS sits at ~22 deg. S planetographic latitude, while the LRS resides at ~33 deg. S latitude. Both vortices deflect nearby eastward and westward winds jets around their periphery, and are somewhat confined to their latitude bands by the alternating, and nearly constant, zonal wind field. However, they do oscillate slightly in latitude, particularly near the times of a passage, in part because the deflected wind jets push to keep the spots separated. It is during these passages that the LRS, and its predecessor white ovals, is most likely to show changes in size and morphology, which are related to the internal wind fields and regulate the vertical cloud structure of the vortex. For example, GRS passages in 1998 and 2000 preceded the merger of the three white ovals into the single large Oval BA, after the ovals and intervening cyclonic cells were deflected by the GRS.

We propose to study the 2008 passage to look for changes in internal vortex winds, nearby zonal winds and vortex upper cloud structure, particularly in particle size and opacity, using five orbits of WFPC2 and two orbits of NICMOS. These data will be combined with a multitude of planned ground-based coverage to offer an unprecedented view of a GRS/Oval passage, which will give insight on cloud structure, dynamics, and possibly even water abundance below the cloud decks (water abundance governs the distance of interaction between the two spots). HST is required to provide adequate spatial resolution and wavelength coverage while observing the passage. The 2008 passage is expected to be especially important, as Jupiter underwent a global upheaval in 2007, with disturbances near the GRS and LRS. This upheaval began after the normal Cycle 16 proposal deadline, raising the priority of these observations enough to warrant a request for HST time.

WFPC2 11235

HST NICMOS Survey of the Nuclear Regions of Luminous Infrared Galaxies in the Local Universe

At luminosities above 10^11.4 L_sun, the space density of far-infrared selected galaxies exceeds that of optically selected galaxies. These `luminous infrared galaxies’ {LIRGs} are primarily interacting or merging disk galaxies undergoing enhanced star formation and Active Galactic Nuclei {AGN} activity, possibly triggered as the objects transform into massive S0 and elliptical merger remnants. We propose NICMOS NIC2 imaging of the nuclear regions of a complete sample of 88 L_IR > 10^11.4 L_sun luminous infrared galaxies in the IRAS Revised Bright Galaxy Sample {RBGS: i.e., 60 micron flux density > 5.24 Jy}. This sample is ideal not only in its completeness and sample size, but also in the proximity and brightness of the galaxies. The superb sensitivity and resolution of NICMOS NIC2 on HST enables a unique opportunity to study the detailed structure of the nuclear regions, where dust obscuration may mask star clusters, AGN and additional nuclei from optical view, with a resolution significantly higher than possible with Spitzer IRAC. This survey thus provides a crucial component to our study of the dynamics and evolution of IR galaxies presently underway with Wide-Field, HST ACS/WFC and Spitzer IRAC observations of these 88 galaxies. Imaging will be done with the F160W filter {H-band} to examine as a function of both luminosity and merger stage {i} the luminosity and distribution of embedded star clusters, {ii} the presence of optically obscured AGN and nuclei, {iii} the correlation between the distribution of 1.6 micron emission and the mid- IR emission as detected by Spitzer IRAC, {iv} the evidence of bars or bridges that may funnel fuel into the nuclear region, and {v} the ages of star clusters for which photometry is available via ACS/WFC observations. The NICMOS data, combined with the HST ACS, Spitzer, and GALEX observations of this sample, will result in the most comprehensive study of merging and interacting galaxies to date.

WFPC2 11233

Multiple Generations of Stars in Massive Galactic Globular Clusters

This is a follow-up to recent HST imaging of NGC 2808, which discovered that its main sequence is triple, with three well-separated parallel branches {Fig.~1}. Along with the double MS of Omega Centauri, this challenges the long-held paradigm that globular clusters are simple, single stellar populations. The cause of this main sequence multiplicity in both clusters is likely to be differences in helium abundance, which could play a fundamental role in the understanding of stellar populations. We propose to image seven more of the most massive globular clusters, to examine their main sequences for indications of splitting.

NIC2 11219

Active Galactic Nuclei in nearby galaxies: a new view of the origin of the radio-loud radio-quiet dichotomy?

Using archival HST and Chandra observations of 34 nearby early-type galaxies {drawn from a complete radio selected sample} we have found evidence that the radio-loud/radio-quiet dichotomy is directly connected to the structure of the inner regions of their host galaxies in the following sense: [1] Radio-loud AGN are associated with galaxies with shallow cores in their light profiles [2] Radio-quiet AGN are only hosted by galaxies with steep cusps. Since the brightness profile is determined by the galaxy’s evolution, through its merger history, our results suggest that the same process sets the AGN flavour. This provides us with a novel tool to explore the co-evolution of galaxies and supermassive black holes, and it opens a new path to understand the origin of the radio-loud/radio-quiet AGN dichotomy. Currently our analysis is statistically incomplete as the brightness profile is not available for 82 of the 116 targets. Most galaxies were not observed with HST, while in some cases the study is obstructed by the presence of dust features. We here propose to perform an infrared NICMOS snapshot survey of these 82 galaxies. This will enable us to i} test the reality of the dichotomic behaviour in a substantially larger sample; ii} extend the comparison between radio-loud and radio-quiet AGN to a larger range of luminosities.

FGS 11210

The Architecture of Exoplanetary Systems

Are all planetary systems coplanar? Concordance cosmogony makes that prediction. It is, however, a prediction of extrasolar planetary system architecture as yet untested by direct observation for main sequence stars other than the Sun. To provide such a test, we propose to carry out FGS astrometric studies on four stars hosting seven companions. Our understanding of the planet formation process will grow as we match not only system architecture, but formed planet mass and true distance from the primary with host star characteristics for a wide variety of host stars and exoplanet masses. We propose that a series of FGS astrometric observations with demonstrated 1 millisecond of arc per-observation precision can establish the degree of coplanarity and component true masses for four extrasolar systems: HD 202206 {brown dwarf+planet}; HD 128311 {planet+planet}, HD 160691 =3D mu Arae {planet+planet}, and HD 222404AB =3D gamma Cephei {planet+star}. In each case the companion is identified as such by assuming that the minimum mass is the actual mass. For the last target, a known stellar binary system, the companion orbit is stable only if coplanar with the AB binary orbit.

WFPC2/NIC3 11209

Determining the Structural Parameters of the First Globular Cluster Found to Host an Black-Hole X-ray Binary

We recently published the discovery of the first black hole X-ray binary in a globular cluster. This object is located in a bright globular cluster around the Virgo elliptical NGC 4472. Here we propose to obtain HST PC images of this black- hole hosting globular cluster and a sample of other NGC 4472 globulars. We will use these data to determine the structural parameters of both the globular cluster known to have a black hole and a control sample of other NGC 4472 clusters. This will test recent theoretical predictions how black holes affect the structural parameters of globular clusters, and more generally will allow for the first time constraints on any relationship between the presence of a black hole and the surface brightness profiles of globular clusters. The deep WFPC2 images outside of the galaxy’s central regions will also be invaluable for studying how the sizes and luminosity function of globular clusters depend on distance from the center of the galaxy, and thus address questions about the origin of the size differences between metal-rich and metal-poor clusters and the shape of the globular cluster luminosity function. In addition, parallel NIC3 images will allow the optical to near-infrared colors of NGC 4472 globular cluster to be determined over a wide range of galactocentric radii.

WFPC2 11202

The Structure of Early-type Galaxies: 0.1-100 Effective Radii

The structure, formation and evolution of early-type galaxies is still largely an open problem in cosmology: how does the Universe evolve from large linear scales dominated by dark matter to the highly non-linear scales of galaxies, where baryons and dark matter both play important, interacting, roles? To understand the complex physical processes involved in their formation scenario, and why they have the tight scaling relations that we observe today {e.g. the Fundamental Plane}, it is critically important not only to understand their stellar structure, but also their dark-matter distribution from the smallest to the largest scales. Over the last three years the SLACS collaboration has developed a toolbox to tackle these issues in a unique and encompassing way by combining new non-parametric strong lensing techniques, stellar dynamics, and most recently weak gravitational lensing, with high-quality Hubble Space Telescope imaging and VLT/Keck spectroscopic data of early-type lens systems. This allows us to break degeneracies that are inherent to each of these techniques separately and probe the mass structure of early-type galaxies from 0.1 to 100 effective radii. The large dynamic range to which lensing is sensitive allows us both to probe the clumpy substructure of these galaxies, as well as their low-density outer haloes. These methods have convincingly been demonstrated, by our team, using smaller pilot-samples of SLACS lens systems with HST data. In this proposal, we request observing time with WFPC2 and NICMOS to observe 53 strong lens systems from SLACS, to obtain complete multi-color imaging for each system. This would bring the total number of SLACS lens systems to 87 with completed HST imaging and effectively doubles the known number of galaxy-scale strong lenses. The deep HST images enable us to fully exploit our new techniques, beat down low-number statistics, and probe the structure and evolution of early-type galaxies, not only with a uniform data-set an order of magnitude larger than what is available now, but also with a fully coherent and self-consistent methodological approach!

WFPC2 11176

Location and the Origin of Short Gamma-Ray Bursts

During the past decade extraordinary progress has been made in determining the origin of long- duration gamma-ray bursts. It has been conclusively shown that these objects derive from the deaths of massive stars. Nonetheless, the origin of their observational cousins, short-duration gamma-ray bursts {SGRBs} remains a mystery. While SGRBs are widely thought to result from the inspiral of compact binaries, this is a conjecture. A number of hosts of SGRBs have been identified, and have been used by some to argue that SGRBs derive primarily from an ancient population {~ 5 Gyr}; however, it is not known whether this conclusion more accurately reflects selection biases or astrophysics. Here we propose to employ a variant of a technique that we pioneered and used to great effect in elucidating the origins of long-duration bursts. We will examine the degree to which SGRB locations trace the red or blue light of their hosts, and thus old or young stellar populations. This approach will allow us to study the demographics of the SGRB population in a manner largely free of the distance dependent selection effects which have so far bedeviled this field, and should give direct insight into the age of the SGRB progenitor population.

WFPC2 11156

Monitoring Active Atmospheres on Uranus and Neptune

We propose Snapshot observations of Uranus and Neptune to monitor changes in their atmospheres on time scales of weeks and months. Uranus equinox is only months away, in December 2007. Hubble Space Telescope observations during the past several years {Hammel et al. 2005, Icarus 175, 284 and references therein} have revealed strongly wavelength- dependent latitudinal structure, the presence of numerous visible-wavelength cloud features in the northern hemisphere, at least one very long-lived discrete cloud in the southern hemisphere, and in 2006 the first dark spot ever seen on Uranus. Long-term ground-based observations {Lockwood and Jerzekiewicz, 2006, Icarus 180, 442; Hammel and Lockwood 2007, Icarus 186, 291} reveal seasonal brightness changes whose origins are not well understood. Recent near-IR images of Neptune obtained using adaptive optics on the Keck Telescope, together with HST observations {Sromovsky et al. 2003, Icarus 163, 256 and references therein} which include previous Snapshot programs {GO 8634, 10170, 10534} show a general increase in activity at south temperate latitudes until 2004, when Neptune returned to a rather Voyager-like appearance. Further Snapshot observations of these two dynamic planets will elucidate the nature of long-term changes in their zonal atmospheric bands and clarify the processes of formation, evolution, and dissipation of discrete albedo features.

WFPC2 11134

WFPC2 Tidal Tail Survey: Probing Star Cluster Formation on the Edge

The spectacular HST images of the interiors of merging galaxies such as the Antennae and NGC 7252 have revealed rich and diverse populations of star clusters created over the course of the interaction. Intriguingly, our WFPC2 study of tidal tails in these and other interacting pairs has shown that star cluster birth in the tails does not follow a similarly straightforward evolution. In fact, cluster formation in these relatively sparse environments is not guaranteed — only one of six tails in our initial study showed evidence for a significant population of young star clusters. The tail environment thus offers the opportunity to probe star cluster formation on the edge of the physical parameter space {e.g., of stellar and gas mass, density, and pressure} that permits it to occur. We propose to significantly extend our pilot sample of optically bright, gas-rich tidal tails by a factor of 4 in number to include a more diverse population of tails, encompassing major and minor mergers, gas-rich and gas-poor tails, as well as early, late, and merged interaction stages. With 21 orbits of HST WFPC2 imaging in the F606W and F814W filters, we can identify, roughly age-date, and measure sizes of star clusters to determine what physical parameters affect star cluster formation. WFPC2 imaging has been used effectively in our initial study of four mergers, and it will be possible in this program to reach similar limits of Mv=3D-8.5 for each of 16 more tails. With the much larger sample we expect to isolate which factors, such as merger stage, HI content, and merger mass ratio, drive the formation of star clusters. =20 WFPC2 11130

AGNs with Intermediate-mass Black Holes: Testing the Black Hole-Bulge Paradigm, Part II

The recent progress in the study of central black holes in galactic nuclei has led to a general consensus that supermassive {10^6-10^9 solar mass} black holes are closely connected with the formation and evolutionary history of large galaxies, especially their bulge component. Two outstanding issues, however, remain unresolved. Can central black holes form in the absence of a bulge? And does the mass function of central black holes extend below 10^6 solar masses? Intermediate-mass black holes {<10^6 solar masses}, if they exist, may offer important clues to the nature of the seeds of supermassive black holes. Using the SDSS, our group has successfully uncovered a new population of AGNs with intermediate-mass black holes that reside in low-luminosity galaxies. However, very little is known about the detailed morphologies or structural parameters of the host galaxies themselves, including the crucial question of whether they have bulges or not. Surprisingly, the majority of the targets of our Cycle 14 pilot program have structural properties similar to dwarf elliptical galaxies. The statistics from this initial study, however, are really too sparse to reach definitive conclusions on this important new class of black holes. We wish to extend this study to a larger sample, by using the Snapshot mode to obtain WFPC2 F814W images from a parent sample of 175 AGNs with intermediate- mass black holes selected from our final SDSS search. We are particularly keen to determine whether the hosts contain bulges, and if so, how the fundamental plane properties of the host depend on the mass of their central black holes. We will also investigate the environment of this unique class of AGNs.

NIC3 11120

A Paschen-Alpha Study of Massive Stars and the ISM in the Galactic Center

The Galactic center (GC) is a unique site for a detailed study of a multitude of complex astrophysical phenomena, which may be common to nuclear regions of many galaxies. Observable at resolutions unapproachable in other galaxies, the GC provides an unparalleled opportunity to improve our understanding of the interrelationships of massive stars, young stellar clusters, warm and hot ionized gases, molecular clouds, large scale magnetic fields, and black holes. We propose the first large-scale hydrogen Paschen alpha line survey of the GC using NICMOS on the Hubble Space Telescope. This survey will lead to a high resolution and high sensitivity map of the Paschen alpha line emission in addition to a map of foreground extinction, made by comparing Paschen alpha to radio emission. This survey of the inner 75 pc of the Galaxy will provide an unprecedented and complete search for sites of massive star formation. In particular, we will be able to (1) uncover the distribution of young massive stars in this region, (2) locate the surfaces of adjacent molecular clouds, (3) determine important physical parameters of the ionized gas, (4) identify compact and ultra-compact HII regions throughout the GC. When combined with existing Chandra and Spitzer surveys as well as a wealth of other multi-wavelength observations, the results will allow us to address such questions as where and how massive stars form, how stellar clusters are disrupted, how massive stars shape and heat the surrounding medium, and how various phases of this medium are interspersed.

WFPC2 11119

The Stellar Origins of Supernovae

Supernovae {SNe} have a profound effect on galaxies, and have been used recently as precise cosmological probes, resulting in the discovery of the accelerating Universe. They are clearly very important events deserving of intense study. Yet, even with nearly 4000 known SNe, we know relatively little about the stars which give rise to these powerful explosions. The main limitation has been the lack of spatial resolution in pre-SN imaging data. However, since 1999 our team has been at the vanguard of directly identifying SN progenitor stars in HST images. From this exciting new line of study, the emerging trend from 5 detections for Type II-Plateau SNe is that their progenitors appear to be relatively low mass {8 to 20 Msun} red supergiants, although more cases are needed. Nonetheless, the nature of the progenitors of Type Ib/c SNe, a subset of which are associated with the amazing gamma-ray bursts, remains ambiguous. Furthermore, we remain in the continually embarrassing situation that we still do not yet know which progenitor systems explode as Type Ia SNe, which are currently being used for precision cosmology. We propose to confirm the identities of the progenitors of 4 SNe within 17 Mpc, which we expect to occur during Cycle 16, through ToO observations using WFPC2/PC.

NIC1 11117

The Search for Atmospheric Water in the Transiting Planet HD189733b

We propose to use the NICMOS camera to search for transit NIR signatures of atmospheric water in HD189733b. While water absorption bands exist in the optical and IR, space-based NIR signatures are uniquely positioned to offer the best chance at detection. Using narrow band photometric filters, we will be able to detect absorption signatures while the planet is in primary transit. A positive detection would be the first proof of water on an extrasolar planet. Furthermore, it would provide invaluable planetary information, constraining the entire chemistry. As a byproduct of the high SNR required for our primary science goal, we will be able to improve on the value of the planetary radius, a result independent of our primary science objective. The accurate radius estimate, together with planet structure models, will allow constraining the planet interior and its relationship with formation models and stellar metallicity.

WFPC2 11113

Binaries in the Kuiper Belt: Probes of Solar System Formation and Evolution

The discovery of binaries in the Kuiper Belt and related small body populations is powering a revolutionary step forward in the study of this remote region. Three quarters of the known binaries in the Kuiper Belt have been discovered with HST, most by our snapshot surveys. The statistics derived from this work are beginning to yield surprising and unexpected results. We have found a strong concentration of binaries among low-inclination Classicals, a possible size cutoff to binaries among the Centaurs, an apparent preference for nearly equal mass binaries, and a strong increase in the number of binaries at small separations. We propose to continue this successful program in Cycle 16; we expect to discover at least 13 new binary systems, targeted to subgroups where these discoveries can have the greatest impact.

NIC3 11107

Imaging of Local Lyman Break Galaxy Analogs: New Clues to Galaxy Formation in the Early Universe

We have used the ultraviolet all-sky imaging survey currently being conducted by the Galaxy Evolution Explorer {GALEX} to identify for the first time a rare population of low-redshift starbursts with properties remarkably similar to high-redshift Lyman Break Galaxies {LBGs}. These “compact UV luminous galaxies” {UVLGs} resemble LBGs in terms of size, SFR, surface brightness, mass, metallicity, kinematics, dust, and color. The UVLG sample offers the unique opportunity of investigating some very important properties of LBGs that have remained virtually inaccessible at high redshift: their morphology and the mechanism that drives their star formation. Therefore, in Cycle 15 we have imaged 7 UVLGs using ACS in order to 1} characterize their morphology and look for signs of interactions and mergers, and 2} probe their star formation histories over a variety of timescales. The images show a striking trend of small- scale mergers turning large amounts of gas into vigorous starbursts {a process referred to as dissipational or “wet” merging}. Here, we propose to complete our sample of 31 LBG analogs using the ACS/SBC F150LP {FUV} and WFPC2 F606W {R} filters in order to create a statistical sample to study the mechanism that triggers star formation in UVLGs and its implications for the nature of LBGs. Specifically, we will 1} study the trend between galaxy merging and SFR in UVLGs, 2} artificially redshift the FUV images to z=3D1-4 and compare morphologies with those in = similarly sized samples of LBGs at the same rest-frame wavelengths in e.g. GOODS, UDF, and COSMOS, 3} determine the presence and morphology of significant stellar mass in “pre- burst” stars, and 4} study their immediate environment. Together with our Spitzer {IRAC+MIPS}, GALEX, SDSS and radio data, the HST observations will form a unique union of data that may for the first time shed light on how the earliest major episodes of star formation in high redshift galaxies came about. This proposal was adapted from an ACS HRC+WFC proposal to meet the new Cycle 16 observing constraints, and can be carried out using the ACS/SBC and WFPC2 without compromising our original science goals.

WFPC2 11103

A Snapshot Survey of The Most Massive Clusters of Galaxies

We propose the continuation of our highly successful SNAPshot survey of a sample of 125 very X-ray luminous clusters in the redshift range 0.3-0.7. As demonstrated by the 25 snapshots obtained so far in Cycle14 and Cycle15 these systems frequently exhibit strong gravitational lensing as well as spectacular examples of violent galaxy interactions. The proposed observations will provide important constraints on the cluster mass distributions, the physical nature of galaxy-galaxy and galaxy-gas interactions in cluster cores, and a set of optically bright, lensed galaxies for further 8-10m spectroscopy. All of our primary science goals require only the detection and characterization of high-surface-brightness features and are thus achievable even at the reduced sensitivity of WFPC2. Because of their high redshift and thus compact angular scale our target clusters are less adversely affected by the smaller field of view of WFPC2 than more nearby systems. Acknowledging the broad community interest in this sample we waive our data rights for these observations. Due to a clerical error at STScI our approved Cycle15 SNAP program was barred from execution for 3 months and only 6 observations have been performed to date – reinstating this SNAP at Cycle16 priority is of paramount importance to reach meaningful statistics.

WFPC2 10905

The Dynamic State of the Dwarf Galaxy Rich Canes Venatici I Region

With accurate distances, the nearest groups of galaxies can be resolved in 3 dimensions and the radial component of the motions of galaxies due to local density perturbations can be distinguished from cosmological expansion components. Currently, with the ACS, galaxy distances within 8 Mpc can be measured effectively and efficiently by detecting the tip of the red giant branch {TRGB}. Of four principal groups at high galactic latitude in this domain, the Canes Venatici I Group {a} is the least studied, {b} is the most populated, though overwhelmingly by dwarf galaxies, and {c} is likely the least dynamically evolved. It is speculated that galaxies in low mass groups may fail to retain baryons as effectively as those in high mass groups, resulting in significantly higher mass-to-light ratios. The CVn I Group is suspected to lie in the mass regime where the speculated astrophysical processes that affect baryon retention are becoming important.


Significant Spacecraft Anomalies: (The following are preliminary reports of potential non-nominal performance that will be investigated.)

HSTARS: 11310 – GSacq(1,2,1) failed to RGA control GSacq(1,2,1) scheduled at 139/22:45:38 failed at 22:50:03 due to search radius limit exceeded on FGS 1. ESB “a05” Exceeded SRL was received. OBAD1 had an RSS value of 4802.35 a-s and OBAD2 had an RSS value of 41.85 a-s.

11311 – REacq(1,2,1) failed to RGA Control REacq(1,2,1)scheduled at 140/03:32:02 failed to RGA control due to search radius limit exceeded on FGS 1. ESB “a05” Exceeded SRL was received. OBAD1 showed errors of V1=3D-428.49, V2=3D-634.65, V3=3D219.34 and RSS =3D 796.55. OBAD2 showed errors of V1=3D-45.94, = V2=3D-26.59,V3=3D-63.00, and RSS=3D82.38.



                       SCHEDULED      SUCCESSFUL

FGS GSacq               27                  26

FGS REacq               16                  15

OBAD with Maneuver      86                  86


SpaceRef staff editor.