Status Report

NASA Hubble Space Telescope Daily Report #4041

By SpaceRef Editor
February 2, 2006
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NASA Hubble Space Telescope Daily Report #4041

HUBBLE SPACE TELESCOPE – Continuing to collect World Class Science


PERIOD COVERED: UT February 01, 2006 (DOY 032)


ACS/HRC 10495

The Nuclear Environment of the Galaxy Hosting the Largest Known Radio Outburst

We propose to image the cD galaxy host of the most powerful radio outburst known in the Universe. The outburst was identified in a Chandra image of a z=0.216 galaxy cluster which revealed a pair of enormous cavities, each 200 kpc in diameter, embedded in its X-ray halo. The outburst began approximately 100 Myr ago and has expended 6×10^61 ergs. It is apparently powered by accretion onto the cD’s billion solar mass nuclear black hole, which grew heavier by roughly 1/3 during the outburst. We intend to examine the morphology and nuclear environment of the host galaxy to understand the conditions that created this remarkable event.

ACS/HRC 10512

Search for Binaries Among Faint Jupiter Trojan Asteroids

We propose an ambitious SNAPSHOT program to survey faint Jupiter Trojan asteroids for binary companions. We target 150 objects, with the expectation of acquiring data on about 50%. These objects span Vmag = 17.5-19.5, a range inaccessible with ground-based adaptive optics. We now have a significant sample from our survey of brighter Trojans to suggest that the binary fraction is similar to that which we find among brighter main-belt asteroids, roughly 2%. However, our observations suggest a higher binary fraction for smaller main-belt asteroids, probably the result of a different formation mechanism {evident also from the physical characteristics of the binaries}. Because the collision environment among the Trojans is similar to that of the Main Belt, while the composition is likely to be very different, sampling the binary fraction among the fainter Trojans should help us understand the collisional and binary formation mechanisms at work in various populations, including the Kuiper Belt, and help us evaluate theories for the origin of the Trojans. Calibration of and constraints on models of binary production and collisional evolution can only be done using these large-scale, real-life physical systems that we are beginning now to find and utilize.


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 Oct, 2 2005- May, 29-2006. The second half of the program has a different proposal number: 10758.

ACS/SBC 10739

Internal Flat Field Stability

The stability of the CCD flat fields will be monitored using the calibration lamps and a sub-sample of the filter set. For the SBC imaging filters, differences in the low-frequency flat field structure with wavelength will be assessed. New high signal P-flats will be obtained for the SBC prisms.

ACS/WFC 10493

A Survey for Supernovae in Massive High-Redshift Clusters

We propose to measure, to an unprecedented 30% accuracy, the SN-Ia rate in a sample of massive z=0.5-0.9 galaxy clusters. The SN-Ia rate is a poorly known observable, especially at high z, and in cluster environments. The SN rate and its redshift dependence can serve as powerful discrimiminants for a number of key issues in astrophysics and cosmology. Our observations will: 1. Put clear constraints on the characteristic SN-Ia “delay time, ” the typical time between the formation of a stellar population and the explosion of some of its members as SNe-Ia. Such constraints can exclude entire categories of SN-Ia progenitor models, since different models predict different delays. 2. Help resolve the question of the dominant source of the high metallicity in the intracluster medium {ICM} – SNe-Ia, or core-collapse SNe from an early stellar population with a top-heavy IMF, perhaps those population III stars responsible for the early re-ionization of the Universe. Since clusters are excellent laboratories for studying enrichment {they generally have a simple star-formation history, and matter cannot leave their deep potentials}, the results will be relevant for understanding metal enrichment in general, and the possible role of first generation stars in early Universal enrichment. 3. Reveal, via nuclear variability, the AGN fraction in clusters at this redshift, to be compared with the field AGN fraction. This will be valuable input for understanding black-hole demographics, AGN evolution, and ICM energetics. 4. Potentially discover intergalactic cluster SNe, which can trace the stripped stellar population at high z.

ACS/WFC 10494

Imaging the mass structure of distant lens galaxies

The surface brightness distribution of extended gravitationally lensed arcs and Einstein rings contains super-resolved information about the lensed object, and, more excitingly, about the smooth and clumpy mass distribution of the lens galaxies. The source and lens information can non-parametrically be separated, resulting in a direct “gravitational-mass image” of the inner mass-distribution of cosmologically-distant galaxies {Koopmans 2005}. With this goal in mind, we propose deep HST ACS-F555W/F814W and NICMOS-F160W imaging of 15 gravitational-lens systems with spatially resolved lensed sources, selected from the 17 new lens systems discovered by the Sloan Lens ACS Survey {Bolton et al. 2004}. Each system has been selected from the SDSS and confirmed in a time-efficient HST-ACS snapshot program {cycle-13}; they show highly-magnified arcs or Einstein rings, lensed by a massive early-type lens galaxy. High- fidelity multi-color HST images are required {not delivered by the 420-sec snapshot images} to isolate these lensed images {properly cleaned, dithered and extinction-corrected} from the lens galaxy surface brightness distribution, and apply our “gravitational-mass imaging” technique. The sample of galaxy mass distributions – determined through this method from the arcs and Einstein ring HST images – will be studied to: {i} measure the smooth mass distribution of the lens galaxies {Dark and luminous mass are separated using the HST images and the stellar M/L values derived from a joint stellar-dynamical analysis of each system}; {ii} quantify statistically and individually the incidence of mass-substructure {with or without obvious luminous counter- parts such as dwarf galaxies}. Since dark-matter substructure should be considerably more prevalent at higher redshift, both results provide a direct test of this prediction of the CDM hierarchical structure-formation model.

ACS/WFC 10543

Microlensing in M87 and the Virgo Cluster

Resolving the nature of dark matter is an urgent problem. The results of the MACHO survey of the Milky Way dark halo toward the LMC indicate that a significant fraction of the halo consists of stellar mass objects. The VATT/Columbia survey of M31 finds a similar lens fraction in the M31 dark halo. We propose a series of observations with ACS that will provide the most thorough search for microlensing toward M87, the central elliptical galaxy of the Virgo cluster. This program is optimized for lenses in the mass range from 0.01 to 1.0 solar masses. By comparing with archival data, we can detect lenses as massive as 100 solar masses, such as the remnants of the first stars. These observations will have at least 15 times more sensitivity to microlensing than any previous survey, e.g. using WFPC2. This is due to the factor of 2 larger area, factor of more than 4 more sensitivity in the I-band, superior pixel scale and longer baseline of observations. Based on the halo microlensing results in the Milky Way and M31, we might expect that galaxy collisions and stripping would populate the overall cluster halo with a large number of stellar mass objects. This program would determine definitively if such objects compose the cluster dark matter at the level seen in the Milky Way. A negative result would indicate that such objects do not populate the intracluster medium, and may indicate that galaxy harassment is not as vigorous as expected. We can measure the level of events due to the M87 halo: this would be the best exploration to date of such a lens population in an elliptical galaxy. Star-star lensing should also be detectable. About 20 erupting classical novae will be seen, allowing to determine the definitive nova rate for this giant elliptical galaxy. We will determine if our recent HST detection of an M87 globular cluster nova was a fluke, or indicative of a 100x higher rate of incidence of cataclysmic variables and nova eruptions in globulars than previously believed. We will examine the populations of variable stars, and will be able to cleanly separate them from microlensing.

ACS/WFC 10573

Globular Clusters in the Direction of the Inner Galaxy

The age, chemical and kinematic distributions of stellar populations provide powerful constraints on models of the formation and evolution of the Milky Way. The globular clusters constitute an especially useful case because the stars within individual clusters are coeval and spatially distinct. But a serious limitation in the study of many globular clusters — especially those located near the Galactic Center — has been the existence of large absolute and differential extinction by foreground dust. We propose to use the ACS to map the differential extinction and remove their effects in a large sample of globular clusters located in the direction of the inner Galaxy using a technique refined recently by von Braun and Mateo {2001}. These observations and their analyses will let us produce high quality color-magnitude diagrams of these poorly studied clusters that will allow us to determine these clusters’ relative ages, distances and chemistry and to address important questions about the formation and the evolution of the inner Galaxy. Our aim for these ACS observations is to obtain data for the most crowded clusters in the inner Galaxy where the excellent spatial resolution of the ACS is most necessary.

ACS/WFC 10696

Galaxy Populations at Very Large Cluster Radii III: The Outskirts of CL J1226.9+3332 at z=0.89

We propose to use the Advanced Camera for Surveys to image 10 selected fields in the outskirts of X-ray luminous cluster Cl J1226.9+3332 at z=0.89, for a detailed study of those galaxies entering the cluster for the first time. These data will be combined with the existing ACS imaging of the inner portions of the cluster, and be analyzed in parallel with our wide-field two- color ACS mosaics of MS 1054–03 {z=0.83} and RX J0152–13 {z=0.83}. Together, these studies of the galaxy populations well beyond the virial radii of the clusters will allow us to directly {1} study the transformation of infalling field spirals into cluster early-types using the morphology-density relation to large radii and very low local densities; {2} measure the frequency of galaxy-galaxy mergers and interactions in the infall region; and {3} determine the star-formation histories of those field galaxies most recently accreted by the cluster, using accurate colors, morphologies, and M/L ratios. The wide-field HST/ACS data will be supplemented with both wide-field multi-object spectroscopy and photometric redshifts from ground-based broadband optical and near-IR imaging. By studying the clusters out to twice their virial radii, the three clusters in our sample will directly test predictions for the formation of early- type galaxies and for the transformation of field galaxies into present-day cluster galaxies.

FGS 10610

Astrometric Masses of Extrasolar Planets and Brown Dwarfs

We propose observations with HST/FGS to estimate the astrometric elements {perturbation orbit semi-major axis and inclination} of extra-solar planets orbiting six stars. These companions were originally detected by radial velocity techniques. We have demonstrated that FGS astrometry of even a short segment of reflex motion, when combined with extensive radial velocity information, can yield useful inclination information {McArthur et al. 2004}, allowing us to determine companion masses. Extrasolar planet masses assist in two ongoing research frontiers. First, they provide useful boundary conditions for models of planetary formation and evolution of planetary systems. Second, knowing that a star in fact has a plantary mass companion, increases the value of that system to future extrasolar planet observation missions such as SIM PlanetQuest, TPF, and GAIA.


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

HSTARS: (None)



                         SCHEDULED      SUCCESSFUL
FGS GSacq               13                     13
FGS REacq                02                     02
OBAD with Maneuver   30                     30


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