NASA Hubble Space Telescope Daily Report #3950
HUBBLE SPACE TELESCOPE – Continuing to collect World Class Science
DAILY REPORT # 3950
PERIOD COVERED: UT September 21, 2005 (DOY 264)
OBSERVATIONS SCHEDULED
ACS/HRC 10572
Resolving M32’s Main Sequence: A Critical Test for Stellar Population Studies
We propose to observe the M32 main-sequence turnoff {MSTO} with deep ACS/HRC B and V images. Only the superior resolution and blue sensitivity of ACS/HRC make this possible. M32 is the only elliptical galaxy close enough to allow direct observation of its MSTO – it is a vital laboratory for deciphering the stellar populations of all other elliptical galaxies, which can only be studied by the spectra of their integrated light, given their greater distances. Major questions about M32’s star formation history remain unanswered. Spectral studies suggest that M32 underwent a recent burst of star formation 3 to 8 billion years ago; observation of the M32 MSTO will confirm this directly. In the process, ACS will easily resolve more luminous components: hot blue stars, luminous, intermediate-age red clump and AGB stars, and any extended blue horizontal branch. These detailed CMDs will provide a direct comparison with population synthesis models for M32, providing a bridge to studies of the integrated light of more distant elliptical galaxies, a crucial ingredient for understanding their star formation histories. As M32 is projected against the edge of the M31 disk, an essential part of our proposal includes deep observation of an M31 disk field to allow the M32 photometry to be background corrected. These observations will reveal the star formation history of M31’s outer disk and are thus of interest in their own right.
ACS/HRC 10602
A Complete Multiplicity Survey of Galactic O2/O3/O3.5 Stars with ACS
Massive stars are preferentially formed in compact multiple systems and clusters and many of them remain spatially unresolved to date, even in our Galaxy. This has hindered the determination of the stellar upper mass limit. The lack of an accurate knowledge of the multiplicity of massive stars can also introduce biases in the calculation of the IMF at its high-mass end. We have recently used ACS/HRC to resolve HD 93129 A, the earliest O-type star known in the Galaxy, into a 55 mas binary. We propose here to extend that work into a complete multi-filter ACS imaging survey of all {20} known O2/O3/O3.5 Galactic stars to characterize the multiplicity of the most massive stars. The data will be combined with existing FGS observations to explore as large a parameter range as possible and to check for consistency. We will also derive the IMF of each system using a crowded-field photometry package and processing the data with CHORIZOS, a code that can derive stellar temperatures, extinctions, and extinction laws from multicolor photometry.
ACS/WFC 10421
Searching for Ancient Mergers in Early Type Host Galaxies of Classical QSOs
Recent HST imaging of QSO host galaxies indicates that at least a large fraction of QSOs reside in seemingly undisturbed elliptical hosts. However, our deep Keck spectroscopy of a sample of these host galaxies indicates that many of these objects were involved in a major starburst episode between 0.6 and 1.6 Gyr ago. We propose to obtain very deep ACS WFC observations of the five hosts in this sample that have the most reliable age determinations to search for fine structure indicative of a past merger event and to test the hypothesis that the elliptical hosts are the products of relatively recent merger events rather than old galaxies which formed at high redshifts. By establishing a firm connection between ancient mergers and the aging starbursts in these classical QSOs, we will be able to estimate the fraction of the total QSO population that results directly from mergers accompanied by massive starbursts and to place constraints on the duty cycle for QSO activity.
ACS/WFC 10496
Decelerating and Dustfree: Efficient Dark Energy Studies with Supernovae and Clusters
We propose a novel HST approach to obtain a dramatically more useful “dust free” Type Ia supernovae {SNe Ia} dataset than available with the previous GOODS searches. Moreover, this approach provides a strikingly more efficient search-and-follow-up that is primarily pre- scheduled. The resulting dark energy measurements do not share the major systematic uncertainty at these redshifts, that of the extinction correction with a prior. By targeting massive galaxy clusters at z > 1 we obtain a five-times higher efficiency in detection of Type Ia supernovae in ellipticals, providing a well-understood host galaxy environment. These same deep cluster images then also yield fundamental calibrations required for future weak lensing and Sunyaev-Zel’dovich measurements of dark energy, as well as an entire program of cluster studies. The data will make possible a factor of two improvement on supernova constraints on dark energy time variation, and much larger improvement in systematic uncertainty. They will provide both a cluster dataset and a SN Ia dataset that will be a longstanding scientific resource.
ACS/WFC 10497
Cepheid Calibrations of the Luminosity of Two Reliable Type Ia Supernovae and a Re- determination of the Hubble Constant
We propose to determine the luminosity of two type Ia supernovae {SNe Ia}, 1995al in NGC 3021 and SN 2002fk in NGC 1309, by observing Cepheids in their spiral hosts. Modern CCD photometry yields an extremely tight Hubble diagram for SNe Ia with a precisely determined intercept {i.e., Delta H_0/H_0}. Yet, the measurement of the true Hubble constant via SNe Ia is limited by the calibration derived from problematic and unreliable SN data. Most of the SNe Ia calibrated by HST to date are significantly compromised by the systematics of photographic photometry, high reddening and SN peculiarity, and by the photometric anomolies associated with WFPC2. The extended reach of ACS now provides opportunities to more reliably calibrate SNe Ia and H_0. Our Cepheid calibration of a reliable SN Ia dataset, SN 1994ae, using ACS in Cycle 11 resulted in a 15% increase in H_0 from the value derived by the HST SN Ia Calibration Program. Yet, there remains a terribly small sample of reliable SN Ia data sets on which to base such a crucial cosmological result. SN 1995al and SN 2002fk are two of the best observed SNe Ia both with little reddening. They provide two opportunities to use ACS for placing the calibration of H_0 via SN Ia on firmer footing and potentially improve its precision.
WFPC2 10356
WFPC2 Cycle 13 Decontaminations and Associated Observations
This proposal is for the monthly WFPC2 decons. Also included are instrument monitors tied to decons: photometric stability check, focus monitor, pre- and post-decon internals {bias, intflats, kspots, & darks}, UV throughput check, VISFLAT sweep, and internal UV flat check.
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.)
HSTARS: (None)
COMPLETED OPS REQUEST: (None)
COMPLETED OPS NOTES: (None)
SCHEDULED SUCCESSFUL FGS Gsacq 5 5 FGS Reacq 10 10 OBAD with Maneuver 30 30
SIGNIFICANT EVENTS: (None)
