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Daily Report #4829
HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science
DAILY REPORT***** #4829 PERIOD COVERED: 5am April 8 - 5am April 9, 2009 (DOY 098/0900z-099/0900z) OBSERVATIONS SCHEDULED ACS/SBC 11982 Spanning the Reionization History of IGM Helium: a Large and Efficient HST Spectral Survey of Far-UV-Bright Quasars The reionization of IGM helium is thought to have occurred at redshifts of z=3 to 4. Detailed studies of HeII Lyman-alpha absorption toward a handful of QSOs at 2.7z3.3 demonstrated the high potential of such IGM probes, but the small sample size and redshift range limit confidence in cosmological inferences. The requisite unobscured sightlines to high-z are extremely rare, but we've cross-correlated 10, 000 z2.8 SDSS DR7 (and other) quasars with GALEX GR4 UV sources to obtain 550 new, high confidence, sightlines potentially useful for HST HeII studies; and in cycle 15-16 trials we demonstrated the efficacy of our SDSS/GALEX selection approach identifying 9 new HeII quasars at unprecedented 67% efficiency. We propose the first far-UV-bright HeII quasar survey that is both large in scale and also efficient, via 2-orbit reconnaissance ACS/SBC prism spectra toward a highly select subset of 40 new SDSS/GALEX quasars at 3.1z5.1. These will provide a community resource list that includes 5 far-UV-bright (restframe) HeII sightlines in each of 8 redshift bins spanning 3.1z3.9 (and perhaps several objects at z4), enabling superb post-SM4 follow-up spectra with COS or STIS. But simultaneously and independent of any SM4 uncertainties, we will hereby directly obtain 10-orbit UV spectral stacks from the 5 HeII quasars in each of the 8 redshift bins to trace the reionization history of IGM helium over at least 3.1z3.9. These spectral stacks will average over cosmic variance and individual object pathology. Our new high-yield HeII sightline sample and spectral stacks, covering a large redshift range, will allow confident conclusions about the spectrum and evolution of the ionizing background, the evolution of HeII opacity, the density of IGM baryons, and the epoch of helium reionization. WFPC2 11975 UV Light from Old Stellar Populations: a Census of UV Sources in Galactic Globular Clusters In spite of the fact that HST has been the only operative high-resolution eye in the UV-window over the last 18 years, no homogeneous UV survey of Galactic globular clusters (GGCs) has been performed to date. In order to fill this gap in the stellar population studies, we propose a program that exploits the unique capability of the WFPC2 and the SBC in the far-/mid- UV for securing deep UV imaging of 46 GGCs. The proposed observations will allow to study with unprecedented accuracy the hottest GGC stars, comprising the extreme horizontal branch (HB) stars and their progeny (the so-called AGB-manque', and Post-early AGB stars), and "exotic stellar populations" like the blue straggler stars and the interacting binaries. The targets have been selected to properly sample the GGC metallicity/structural parameter space, thus to unveil any possible correlation between the properties of the hot stellar populations and the cluster characteristics. In addition, most of the targets have extended HB "blue tails", that can be properly studied only by means of deep UV observations, especially in the far-UV filters like the F160BW, that is not foreseen on the WFC3. This data base is complemented with GALEX observations in the cluster outermost regions, thus allowing to investigate any possible trend of the UV-bright stellar types over the entire radial extension of the clusters. Although the hottest GGC stars are just a small class of "special" objects, their study has a broad relevance in the context of structure formation and chemical evolution in the early Universe, bringing precious information on the basic star formation processes and the origin of blue light from galaxies. Indeed, the proposed observations will provide the community with an unprecedented data set suitable for addressing a number of still open astrophysical questions, ranging from the main drivers of the HB morphology and the mass loss processes, to the origin of the UV upturn in elliptical galaxies, the dating of distant systems from integrated light, and the complex interplay between stellar evolution and dynamics in dense stellar aggregates. In the spirit of constructing a community resource, we entirely waive the proprietary period for these observations. WFPC2 11987 The Recent Star Formation History of SINGS Galaxies The Spitzer Legacy project SINGS provided a unique view of the current state of star formation and dust in a sample of galaxies of all Hubble types. This multi-wavelength view allowed the team to create current star formation diagnostics that are independent of the dust content and increased our understanding of the dust in galaxies. Even so, using the SINGS data alone we can only make rough estimates of the recent star formation history of these galaxies. The lack of U-band observations means that it is impossible to estimate the ages of young clusters. In addition, the low resolution of the Spitzer and ground-based observations means that what appear to be individual Spitzer sources can actually be composed of many individual clusters with varying ages. In this proposal we plan to address this missing area in SINGS by obtaining high-resolution WFPC2 UBVI observations to accurately find and determine the ages of the young stellar clusters in a subset of the SINGS galaxies. These observations will greatly enhance the legacy value of the SINGS observations while also directly answering questions pertaining to star formation in galaxies. FLIGHT OPERATIONS SUMMARY: Significant Spacecraft Anomalies: (The following are preliminary reports of potential non-nominal performance that will be investigated.) HSTARS: (None) COMPLETED OPS REQUEST: (None) COMPLETED OPS NOTES: (None) *********************** SCHEDULED***** SUCCESSFUL FGS GSAcq************** 06***************** 06 FGS REAcq************** 09***************** 09 OBAD with Maneuver **** 30***************** 30 SIGNIFICANT EVENTS: (None) |
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