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Daily 3761
HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science
DAILY REPORT # 3761 PERIOD COVERED: DOY 356 OBSERVATIONS SCHEDULED ACS/HRC 10165 Determination of orbits and colors for two new binaries in the Koronis asteroid family We propose to measure color and orbital properties of two asteroid binaries in the Koronis family discovered in our SNAP-9747 survey. The best previously studied asteroid binary system, Ida/Dactyl, is also in the Koronis family. Differential space weathering measured on the Ida and Dactyl surfaces has been a powerful constraint on models of satellite formation mechanisms and satellite survivability. HST offers the unique opportunity for similar measurements of these much smaller, main-belt binaries. The new satellites are believed to have formed through different collisional mechanisms than Ida/Dactyl. Further, with a set of 4 relative position measurements for each of the two systems, added to the discovery snapshots, we will determine and compare the densities of the primaries with Ida {a large, 31.5 km, asteroid with density 2.6+-0.5 g/cm^3, measured by the Galileo flyby}. In contrast, {17246} and {22899} are 4.5 km bodies that are likely to have been restructured since the family-forming event by subsequent collisions. As all are members of the same family, differences in density would constrain bulk composition and internal structure {e.g. shard vs. rubble-pile}. Hence, these measurements are likely to further elucidate the mechanisms for formation of satellites. ACS/HRC 10391 Wavelength and Flux Calibration of the ACS prisms The wavelength calibration of the SBC {PR110L and PR130L} and HRC {PR200L} prisms will be established by observing a planetary nebula in the LMC and QSOs at carefully selected redshifts. Flux calibrations will be derived for each prism by observing white dwarf standards. ACS/WFC/WFPC2 10265 The Formation History of Andromeda We propose deep observations of Andromeda's outer disk and giant tidal stream, to reconstruct their star formation histories. As the nearest giant galaxy, Andromeda offers the best testing ground for understanding galaxy formation and evolution. Given the dramatic increase in sensitivity offered by the ACS, we can now resolve stars on the old main sequence in the other giant spiral of the Local Group, and employ the same direct age diagnostics that have been used for decades in the study of Galactic globular clusters. In Cycle 11, we successfully observed a field in the Andromeda halo and constructed a deep color-magnitude diagram reaching well below the oldest main sequence turnoff. In Cycle 13, we propose to extend these observations to the outer disk and tidal stream of Andromeda, to constrain their star formation histories and compare them to that of the halo. The combined observations from these two programs will offer a dramatic advance in our understanding of the overall evolution of spiral galaxies. ACS/WFC/WFPC2 9392 The Ancient Stars of M32 The question of whether the dwarf elliptical galaxy M32 contains a population of truly ancient stars has remained unsettled for decades. We recently used HST/WFPC2 to identify for the first time a population of RR Lyr stars in this galaxy. Since these stars are known only to be present in stellar populations older than 8-10 Gyr, we contend that M32 does possess an old stellar component and certainly cannot be comprised of only intermediate-age {~ 5 Gyr} stars as has been frequently suggested in the literature. Our earlier observations were insufficient to determine even the most basic photometric properties of these stars. Nor could we use the data to identify independent evidence of the old population that could help constrain just what fraction of the galaxy's stars are ancient. We propose new HST/ACS observations to {a} get periods and luminosities of the previously observed RR Lyr stars, {b} search for additional RR Lyr stars in a significantly larger volume of M32, and {c} obtain ultra-deep 2-color photometry to study the ancient main-sequence turnoff region of that galaxy directly, {d} look for radial population gradients in M32, both among the RR Lyr/Horizontal Branch and main- sequence populations, {e} compare the M31/M32 old populations in terms of metallicity spread, and {f} use the RR Lyr stars to precisely determine the relative and possibly the absolute distances of M32 and M31's halo. WFPC2 10132 UV Confirmation of New Quasar Sightlines Suitable for the Study of Intergalactic Helium The reionization of intergalactic helium is thought to have occurred between redshifts of about 3 and 4. The study of HeII Lyman-alpha absorption towards a half-dozen quasars at 2.7z3.5 demonstrates the great potential of such probes of the IGM, but the current critically-small sample limits confidence in resulting cosmological inferences. The requisite unobscured quasar sightlines to high-redshift are extremely rare, especially due to severe absorption in random intervening Lyman-limit systems, but SDSS provides hundreds of bright, new quasars at such redshifts potentially suitable for HeII studies. Our cycle 13 SNAP program proposes to verify the UV detectability of 40 new, bright, z2.9 SDSS quasars, but with special emphasis on extending helium studies to the highest redshift sightlines. Our proposed approach has already proven successful, and additional sightlines will enable follow-up spectal observations to measure the spectrum and evolution of the ionizing background radiation, the density of intergalactic baryons, and the epoch of reionization of the IGM. WFPC2 10360 WFPC2 CYCLE 13 INTERNAL MONITOR This calibration proposal is the Cycle 13 routine internal monitor for WFPC2, to be run weekly to monitor the health of the cameras. A variety of internal exposures are obtained in order to provide a monitor of the integrity of the CCD camera electronics in both bays {gain 7 and gain 15}, a test for quantum efficiency in the CCDs, and a monitor for possible buildup of contaminants on the CCD windows. FLIGHT OPERATIONS SUMMARY: Significant Spacecraft Anomalies: (The following are preliminary reports of potential non-nominal performance that will be investigated.) None COMPLETED OPS REQs: None OPS NOTES EXECUTED: 0900-1 COMMAND PROBLEM @ 357/08:36:25z SCHEDULED SUCCESSFUL FAILURE TIMES FGS Gsacq 06 06 FGS Reacq 09 09 FHST Update 11 11 LOSS of LOCK SIGNIFICANT EVENTS: Secondary Mirror move scheduled first opportunity 357/23:12Z - 23:27Z (OR 17352 with attached script). The STScI has requested a Secondary Mirror move of +4 microns. Last Secondary Mirror move, a +3.6 micron move, was executed 2000.336. |
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