Status Report

NASA Hubble Space Telescope Daily Report #4189

By SpaceRef Editor
August 31, 2006
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NASA Hubble Space Telescope Daily Report #4189

HUBBLE SPACE TELESCOPE – Continuing to collect World Class Science


PERIOD COVERED: UT August 30, 2006 (DOY 242)


ACS/HRC 10860

The largest Kuiper belt object

The past year has seen an explosion in the discoveries of Pluto-sized objects in the Kuiper belt. With the discoveries of the methane-covered 2003 UB313 and 2005 FY9, the multiple satellite system of 2003 EL61, and the Pluto-Charon analog system of Orcus and its satellite, it is finally apparent that Pluto is not a unique oddball at the edge of the solar system, but rather one of a family of similarly large objects in the Kuiper belt and beyond. HST observations over the past decade have been critical for understanding the interior, surface, and atmosphere of Pluto and Charon. We propose here a comprehensive series of observations designed to similarly expand our knowledge of these recently discovered Pluto-sized and near-Pluto-sized Kuiper belt objects. These observations will measure objects’ sizes and densities, explore the outcome of collisions in the outer solar system, and allow the first ever look at the interior structure of a Kuiper belt object. Our wide field survey that discovered all of these objects is nearly finished, so after five years of continuous searching we are finally almost complete in our tally of these near-Pluto-sized objects. This large HST request is the culmination of this half-decade search for new planetary-sized objects. As has been demonstrated repeatedly by the approximately 100 previous orbits devoted to the study of Pluto, only HST has the resolution and sensitivity for detailed study of these distant objects. With these new Pluto-sized objects only now being discovered we have a limited window left to still use HST for these critical observations.


CCD Stability Monitor

This program will verify that the low frequency flat fielding, the photometry, and the geometric distortion are stable in time and across the field of view of the CCD detectors. A moderately crowded stellar field in the cluster 47 Tuc is observed every three months with the HRC {at the cluster core} and WFC {6′ West of the cluster core} using the full suite of broad and narrow band imaging filters. The positions and magnitudes of objects will be used to monitor local and large scale variations in the plate scale and the sensitivity of the detectors and to derive an independent measure of the detector CTE. An additional orbit is required to compare WFC observations taken at gain 1 with those taken at the new default gain 2.


ACS CCDs daily monitor

This program consists of a set of basic tests to monitor, the read noise, the development of hot pixels and test for any source of noise in ACS CCD detectors. The files, biases and dark will be used to create reference files for science calibration. This programme will be for the entire lifetime of ACS. Changes from cycle 13:- The default gain for WFC is 2 e-/DN. As before bias frames will be collected for both gain 1 and gain 2. Dark frames are acquired using the default gain {2}. This program cover the period May, 31 2006- Oct, 1-2006. The first half of the program has a different proposal number: 10729.

ACS/WFC 10505

The Onset of Star Formation in the Universe: Constraints from Nearby Isolated Dwarf Galaxies.

The details of the early star formation histories of tiny dwarf galaxies can shed light on the role in galaxy formation of the reionization which occured at high redshift. Isolated dwarfs are ideal probes since their evolution is not complicated by environmental effects owing to the vicinity of the Milky Way and M31. In addition, dwarf galaxies are the most common type of galaxies, and potentially the building blocks of larger galaxies. Since we can date the oldest stars in them, their study represents a complementary approach to the study of the formation and evolution of galaxies through high-z observations. We propose to use the ACS to obtain a homogeneus dataset of high-quality photometry, down to the old {13 Gyr} main-sequence turnoffs, for a representative sample of 4 isolated Local Group dwarf galaxies. These data are essential to unambiguously determine their early star formation histories, through comparison with synthetic color-magnitude diagrams, and using the constraints provided by their variable stars. Parallel WFPC2 observations of their halos will allow us to reveal the actual nature of their stellar population gradients, providing important aditional constraints on their evolution. The proposed observations are being complemented with ground-based spectroscopy, to obtain metallicity and kinematic information. The observations requested here, which must reach M_I=+3.5 {I=27.5- 28.2} with S/N=10 in crowded systems, can only be achieved with HST using ACS, and won’t be possible with planned ground- or space-based facilities such as JWST. Based on deep WFPC2 observations and ACS image simulations, our team has designed an observational strategy which carefully considers the optimal filter combination, the necessary photometry depth and the effects of stellar crowding.

ACS/WFC 10630

The Fine Structure of Elliptical Galaxies in Voids

Elliptical galaxies constitute a remarkably homogeneous class of objects with a tight color- magnitude relation and a well-defined Fundamental Plane. In spite of their bland and symmetrical morphology, they are characterized by a wealth of structural features {such as nuclear disks, dust lanes, shells, blue cores, etc.} which contain important clues to their formation history. Little is known about how and if these sub-structures vary as a function of environment; in fact, due to the morphology density relation, our knowledge of ellipticals is strongly biased towards overdense regions such as clusters. But what of the fine structure of ellipticals in voids? According to theoretical predictions, void galaxies should have different merger histories than those in clusters, which may imply that their fine structure also differs. We address these issues using the exquisite angular resolution of HST/ACS to resolve sub-structures in the most accurately classified sample, to date, of truly isolated ellipticals, identified using the 2dFGRS.


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

HSTARS: (None)


17913-0 – Install TRTT macro @ 242/1412z


                         SCHEDULED      SUCCESSFUL 
FGS GSacq               08                    08 
FGS REacq               05                    05 
OBAD with Maneuver  26                    26 


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