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Daily 3776
HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science DAILY REPORT # 3776 PERIOD COVERED: DOY 013 Next Daily Report will be issued on 1/18/05 due to MLK Holiday. OBSERVATIONS SCHEDULED ACS/WFC 10452 HST/ACS Mosaic of M51 A six-pointing ACS WFC mosaic of the galaxy pair M51 will be obtained in four filters, B, V, I and H-alpha. Four orbits per pointing will allow high-quality S/N images of the entire galaxy. ACS/WFC/NIC2/WFPC2 9873 Main Sequence Turnoff Ages For Second Parameter Clusters in M33 In cycle 5, we were granted 40 orbits to study the early formation history of M33 by investigating the nature of the "second parameter" phenomenon among its globular star clusters. Discovered among the globular clusters of the Milky Way more than 30 years ago, the "second parameter" effect describes the degeneracy in the behavior of horizontal branch {HB} morphology with metal abundance. This degeneracy implies the existence of a second parameter, which, in addition to metal abundance, influences the morphology of the HB. We constructed {V, V-I} color-magnitude diagrams for 10 M33 halo globular clusters. From these diagrams, we measured the cluster metallicities and HB morphologies. Surprisingly, 8 of the 10 clusters display extremely red horizontal branches, with most of the HB stars lying near or on top of the red giant branch, yet their metal abundances are in the range -1.6 = [Fe/H] = -1.0. A likely explanation is that the halo clusters in M33 are several Gyr younger than those in the Milky Way. To test this hypothesis, we propose to obtain main sequence turnoff photometry for two of our M33 clusters with similar metallicities but vastly differing HBs - a so-called `second parameter pair.' This will help to answer the question of whether age is the second parameter among the M33 halo clusters and provide an important clue to the overall nature of the second parameter effect. ACS/WFC/NIC3 10127 Imaging a protocluster at z=3.1: Effects of environment and evolution on galaxy populations in the early universe We propose imaging a rich protocluster, 0316-26 at z = 3.13, with 31 confirmed Lya cluster members. The bright radio galaxy host is identified with the progenitor of the dominant cluster galaxy. Because its redshift places Lya into an ACS narrow-band filter, the protocluster provides a unique laboratory for studying galaxies at a crucial epoch in the evolution of the Universe. We shall {i} measure and compare sizes, morphologies and colors of galaxies from populations detected using 4 different selection techniques {Lyman and 4000A breaks, Lya and [OIII] excesses}, {ii} study effects of an overdense environment by comparing the properties of protocluster galaxies with z~3 field galaxies from GOODS, {iii} study effects of evolution by relating our data to observations of similar protocluster/cluster targets at redshifts z = 4.1, 2.2, and 1.2, and {iv} constrain the formation of the most massive cluster galaxies by investigating the spatial distribution, Lya equivalent widths and other properties within the 5" radio galaxy host. The ultimate aim is to disentangle the history of structure development and stellar evolution for rich clusters of galaxies. ACS/WFC/WFPC2 10242 Pre-History of a Starburst: Deep Imaging of IC 10 The peculiar Local Group dwarf galaxy IC 10 is the nearest case of a starburst in progress. Starburst galaxies are a prime laboratory for studying the physical processes which regulate star formation in galaxies; as the closest example, IC 10 is potentially the key galaxy for understanding the starburst phenomenon. We propose to obtain deep optical images of IC 10 with the ACS/WFC to achieve three main goals: 1} To make the first estimates of the pre-burst history of IC 10 based on morphological and statistical analysis of its {V, I} color-magnitude diagram; 2} to search for evidence of a past history of burst-dormancy cycles; and 3} to explore the connection between the ages and locations of bright stars and the large-scale structure of the interstellar medium. The distance {0.8 Mpc}, extinction {2.5 mag}, and high surface brightness of IC 10 make these goals unobtainable except with HST. The observations proposed here will yield far and away the deepest images, in absolute magnitudes, ever obtained for any starburst galaxy. Our photometry will reach to magnitudes {V, I} = {28.5, 27.5}, which is below the level of the red clump/horizontal branch and the location of the main-sequence turnoff of stars as old as a billion years. For the first time, it will be possible to measure the detailed history of a starburst host for the Gigayear time period leading up to the burst. The horizontal branch morphology and colors will provide new information on the metallicity and age distribution of stars spanning the entire age of IC 10. Because of its close distance, IC 10 is the ONLY starburst galaxy for which this type of information is obtainable now or in the next decade. We propose to use WFPC2 in parallel to search for a low-surface brightness population associated with the neutral gas filaments surrounding IC 10. NICMOS 8790 NICMOS Post-SAA calibration - CR Persistence Part 1. 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. 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 10357 Saturn's Inner Satellites at True Opposition We request one HST orbit to observe Janus, Epimetheus, Mimas, and Enceladus with WFPC2 exactly at opposition, when the Earth transits the center of the solar disk seen from Saturn on UT 13/14 January 2005. Data obtained at this unique viewing geometry are essential to determining physical properties of the moon's surface, related to its emplacement and evolution, and critical for the interpretation of photometric data obtained by Cassini at higher phase angles. This single observation will be the capstone of 9 years of legacy HST WFPC2 observations of the Saturnian system {Cycles 6-12, R. French, PI} from which we have constructed precise, multiwavelength phase curves which demonstrate how the reflectance of these satellites varies with solar phase angle from 0.07 to 6.4 degrees. Each satellite exhibits a dramatic increase in brightness, or "opposition effect", as phase angles decrease below 1 degree. Since 1998 {Cycle 7} the minimum observable phase angle at opposition has decreased each year to 0.07 degrees in Cycle 12; however, the absolute minimum observable phase angle, about 0.02 degrees {limited by the angular size of the Sun viewed from Saturn}, has not been accessible until Cycle 13. Using the same set of broadband filters for continuity with our previous programs, we will place observations made during the Earth transit on the existing UVBRI phase curves and establish the amplitude of each satellite's opposition surge. From these observations we will determine surface properties such as porosity, grain size distribution and particle opacity using radiative transfer models. While the Cassini spacecraft will obtain images at larger phase angles, it will miss entirely the narrow brightness surge near opposition due to orbital constraints. Because these inner satellites will be either lost in or contaminated by the glare of the fully open rings, they are not accessible to ground-based telescopes. The 2005 opposition presents the only opportunity for HST to observe the Saturnian system during this rare planetary alignment. The next transit of Earth across the solar disk seen from Saturn occurs in 2020; the next central transit occurs in 2049. 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: None SCHEDULED SUCCESSFUL FAILURE TIMES FGS Gsacq 06 06 FGS Reacq 10 10 FHST Update 09 09 LOSS of LOCK SIGNIFICANT EVENTS: None |
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