Status Report

NASA Hubble Space Telescope Daily Report #4066

By SpaceRef Editor
March 9, 2006
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NASA Hubble Space Telescope Daily Report #4066

HUBBLE SPACE TELESCOPE – Continuing to collect World Class Science


PERIOD COVERED: UT March 08, 2006 (DOY 067)


ACS/HRC 10396

Star Clusters, Stellar Populations, and the Evolution of the Small Magellanic Cloud

As the closest star forming dwarf galaxy, the SMC is the preferred location for detailed studies of this extremely common class of objects. We therefore propose to use the capabilities of ACS, which provide an improvement by an order of magnitude over what is possible with ground- based optical imaging surveys that are limited by confusion anddepth, to measure key stellar population parameters in the SMC from VI color-magnitude diagrams. Our program focuses on regions where crowding makes HST essential and includes 7 star clusters and 7 field star locations. We will measure accurate ages of the clusters, test stellar evolution models, gain fiducial stellar sequences to use in fitting the field stars, check the form of the IMF, and substantially extend the study of RR Lyrae variables in the key NGC121 SMC globular cluster. The field pointings will allow us to reconstruct the star formation history, look for enhanced star formation that is expected when the SMC interacts with the LMC and/or Milky Way, and compare its main sequence luminosity {and mass} functions with those of the Milky Way, LMC, and UMi dwarf spheroidal. This proposal is part of a coordinated HST and ground-based study of the stellar history and star formation processes in the SMC.


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 10231

Tracing the Reionization History of Intergalactic Helium out to Redshift 3.8

We have found He II absorption in a quasar at redshift 3.82 via our Cycle 12 program of UV snapshots. This is the highest redshift yet at which He II absorption has been observed, and we propose to study helium ionization in the IGM along this new, long, unobscured sightline to high- redshift. The object has UV flux comparable to that of the rare handful of other z>3 quasars known to be suitable for helium studies, and it is also in the Continuous Viewing Zone. The proposed spectrum will allow us to study the evolution and properties of the IGM and ionizing radiation from z=3.8 {the IGM environment near the quasar} all the way down to z=2.8. This redshift range may span the epoch of helium reionization, and even extends to high enough redshift to enable improved helium opacity measures using both He II Ly-alpha and Ly-beta. This program is now approved to use ACS prism.

ACS/WFC 10475

An ACS H-alpha Survey of the Carina Nebula

We propose an H-alpha ACS imaging survey covering 540 square arcminutes of the Carina Nebula, including an unbiased survey of the bright core, and several prominent dust pillars in the rich southern region of the nebula. Carina provides an important link between well-studied nearby H II regions like Orion, and more distant mini-starbusts like 30 Doradus. CVZ orbits will allow extremely efficient use of HST to map a large area of this complex and important region — more than 95 percent of the proposed survey will be observed by HST for the first time. This survey will provide a complete census of microjets, proplyds, and silhouette disks with diameters as small as 200 AU, enough to spatially resolve disks like those in Orion, and will provide the first catalog of outflows {jets} from embedded low-mass stars, thin filamentary shocks, and wind-wind collisions in Carina. An accurate census of these phenomena is needed to characterize the star formation activity and gas dynamics as a function of position in the nebula, and to determine if models for protoplanetary disk evaporation from Orion are applicable in more extreme regions. Our previous ground-based optical and IR surveys have already revealed dozens of candidates for this type of activity — but this is just the tip of the iceberg. Our proposed HST/ACS survey promises to be a bonanza for understanding ongoing low-mass star formation influenced by extremely high-mass stars.

ACS/WFC 10587

Measuring the Mass Dependence of Early-Type Galaxy Structure

We propose two-color ACS-WFC Snapshot observations of a sample of 118 candidate early- type gravitational lens galaxies. Our lens-candidate sample is selected to yield {in combination with earlier results} an approximately uniform final distribution of 40 early-type strong lenses across a wide range of masses, with velocity dispersions {a dynamical proxy for mass} ranging from 125 to 300 km/s. The proposed program will deliver the first significant sample of low-mass gravitational lenses. All of our candidates have known lens and source redshifts from Sloan Digital Sky Survey data, and all are bright enough to permit detailed photometric and stellar- dynamical observation. We will constrain the luminous and dark-matter mass profiles of confirmed lenses using lensed-image geometry and lens-galaxy structural/photometric measurements from HST imaging in combination with dynamical measurements from spatially resolved ground-based follow-up spectroscopy. Hence we will determine, in unprecedented detail, the dependence of early-type galaxy mass structure and mass-to-light ratio upon galaxy mass. These results will allow us to directly test theoretical predictions for halo concentration and star-formation efficiency as a function of mass and for the existence of a cuspy inner dark- matter component, and will illuminate the structural explanation behind the fundamental plane of early-type galaxies. The lens-candidate selection and confirmation strategy that we propose has been proven successful for high-mass galaxies by our Cycle 13 Snapshot program {10174}. The program that we propose here will produce a complementary and unprecedented lens sample spanning a wide range of lens-galaxy masses.

ACS/WFC 10740

Absolute Photometric & Spectrophometric Calibration

This program has several goals: 1.}Verify repeatability of the ACS instrumentation on a single bright star to +/-0.2%. 2.}Determine any shift in the filter bandpasses since the preflight lab measurements. 3.}Determine the relative magnitude of the 3 primary WD calibrators to 0.1%. 4.}Refine the sensitivity calibration of the CCD prism and grisms at field center and determine the repeatability accuracy of this calibration. 5.}Determine the level of variability of the three HST red standard stars: VB-8 {M7}, 2M0038+18 {L3.5} and 2M0559-14 {T5}, and also measure their short wavelength {<7000A} fluxes. 6.}Cross calibrate with a faint STIS and NICMOS standard WD and solar analog star.


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

HSTARS: (None)



                         SCHEDULED      SUCCESSFUL
FGS GSacq               07                    07
FGS REacq               05                    05
OBAD with Maneuver  24                    24


SpaceRef staff editor.