NASA Hubble Space Telescope Daily Report #4022

HUBBLE SPACE TELESCOPE – Continuing to collect World Class Science

DAILY REPORT # 4022

PERIOD COVERED: UT January 05, 2006 (DOY 005)

OBSERVATIONS SCHEDULED

ACS/HRC 10476

Accurate Mass Determination of the Ancient White Dwarf ER 8 Through Astrometric Microlensing

We propose to determine the mass of the very cool white dwarf ER 8 through astrometric microlensing. We have predicted that ER 8 will pass very close to a 15th-mag background star in January 2006, with an impact parameter of less than 0.05 arcsec. As it passes in front, it will cause a deflection of the background star’s image by >8 milliarcsec, an amount easily detectable with HST/FGS. The gravitational deflection angle depends only on the distances and relative positions of the stars, and on the mass of the white dwarf. Since the distances and positions can be determined precisely before the event, the astrometric measurement offers a unique and direct method to measure the mass of the white dwarf to high accuracy {<5%}. Unlike all other stellar mass determinations, this technique works for single stars {but only if they are nearby and of sufficient mass}. The mass of ER 8 is of special interest because it is a member of the Galactic halo, and appears to be the oldest known field white dwarf. This object can thus set a lower limit on the age of the Galactic halo, but since white-dwarf cooling rates depend on their masses, the mass is a necessary ingredient in the age determination. As a byproduct, we will obtain an accurate parallax for ER 8, and thus its luminosity and {from its effective temperature} its radius. Such quantities are at present rather poorly known for the coolest white dwarfs, and will provide strong constraints on white-dwarf physics.

ACS/WFC 10626

A Snapshot Survey of Brightest Cluster Galaxies and Strong Lensing to z = 0.9

We propose an ACS/WFC snapshot survey of the cores of 150 rich galaxy clusters at 0.3 < z < 0.9 from the Red Sequence Cluster Survey {RCS}. An examination of the galaxian light in the brightest cluster galaxies, coupled with a statistical analysis of the strong-lensing properties of the sample, will allow us to contrain the evolution of both the baryonic and dark mass in cluster cores, over an unprecedented redshift range and sample size. In detail, we will use the high- resolution ACS images to measure the metric {10 kpc/h} luminosity and morphological disturbances around the brightest clusters galaxies, in order to calibrate their accretion history in comparison to recent detailed simulations of structure formation in cluster cores. These images will also yield a well-defined sample of arcs formed by strong lensing by these clusters; the frequency and detailed distribution {size, multiplicity, redshifts} of these strong lens systems sets strong constraints on the total mass content {and its structure} in the centers of the clusters. These data will also be invaluable in the study of the morphological evolution and properties of cluster galaxies over a significant redshift range. These analyses will be supported by extensive ongoing optical and near-infrared imaging, and optical spectroscopy at Magellan, VLT and Gemini telescopes, as well as host of smaller facilities.

ACS/WFC/WFPC2/NIC3 10395

Environmental drivers of galaxy evolution: an HST survey of dwarf galaxy morphologies in the Abell

Galaxies in dense environments are subject to numerous physical processes that leave a lasting impact, yet studies of galaxy evolution to date have been limited to the most luminous galaxies — those least sensitive to environmental influence. We propose to explore the environmental drivers of DWARF galaxy evolution: with a mosaic of 9×9 ACS pointings in F606W we will determine morphologies for ~1200 galaxies down to M_V=-14 in the A901/902 supercluster, spanning 3×3 Mpc at z=0.16. The deep ACS data will allow us to probe their surface brightness profiles, shapes, sizes, asymmetry and fine structure such as tidal features. With the addition of extensive existing multi-wavelength data, we will probe the dependence of these important parameters on dark matter content {from weak lensing maps}, the hot intercluster medium {from deep XMM-Newton imaging}, and local galaxy density {from hyper-accurate COMBO-17 photometric redshifts with delta z=0.02 to m_R=24}, thus disentangling the various environmental processes shaping dwarf galaxy evolution. Furthermore, the 8000+ background galaxies at 0.2< z <1.0 will be of enormous scientific benefit for additional studies of weak lensing, AGN host galaxies, the morphology-density relation, and the merger rate as a function of redshift.

FGS 10614

Internal Structure and Figures of Binary Asteroids

The goal of this proposal is to obtain very important information on the internal structure of a number of asteroids, and insight on the gravitational reaccumulation-process after a catastrophic disruptive collision. High resolutions observations with the HST/FGS interferometer are proposed to obtain high precision data for the topographic shape and size of a number of selected asteroids. Here we focus on objects with satellites, hence with known masses, so that the bulk density and porosity will be derived in the most accurate manner. This will yield plausible estimates on the internal properties of the objects, test wether they are close or not to figures of equilibrium {in terms of shape and adimensional rotational frequency}, and provide estimates of their relative density. The HST/FGS in interferometric mode is an ideal facility to carry out this program.

NIC1/NIC2/NIC3 8792

NICMOS Post-SAA calibration – CR Persistence Part 3

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. The keyword ‘USEAFTER=date/time’ will also be added to the header of each POST-SAA DARK frame. The keyword must be populated with the time, in addition to the date, because HST crosses the SAA ~8 times per day so each POST-SAA DARK will need to have the appropriate time specified, for users to identify the ones they need. Both the raw and processed images will be archived as POST-SAA DARKSs. Generally we expect that all NICMOS science/calibration observations started within 50 minutes of leaving an SAA will need such maps to remove the CR persistence from the science images. Each observation will need its own CRMAP, as different SAA passages leave different imprints on the NICMOS detectors.

NIC1/NIC2/NIC3 8793

NICMOS Post-SAA calibration – CR Persistence Part 4

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. The keyword ‘USEAFTER=date/time’ will also be added to the header of each POST-SAA DARK frame. The keyword must be populated with the time, in addition to the date, because HST crosses the SAA ~8 times per day so each POST-SAA DARK will need to have the appropriate time specified, for users to identify the ones they need. Both the raw and processed images will be archived as POST-SAA DARKSs. Generally we expect that all NICMOS science/calibration observations started within 50 minutes of leaving an SAA will need such maps to remove the CR persistence from the science images. Each observation will need its own CRMAP, as different SAA passages leave different imprints on the NICMOS detectors.

NIC3/ACS/WFC 10404

The Nature of Protocluster Galaxies at z=2.16: Morphology-Density and Color-Magnitude Relations

To establish the epoch when galaxy environment manifests itself as a large-scale evolutionary process, we propose to extend the study of galaxy colors and morphologies to a protocluster at z=2.16. Here the universe is only 3 Gyrs old and significant differences are expected between scenarios favoring a morphology-radius relation over a morphology-density relation. In addition, because the fractional age differences among cluster galaxies are larger, study of the color- magnitude relation provides considerable leverage for determining the epoch of early-type galaxy formation. To facilitate direct comparison to studies at lower redshift, one must probe the same rest-frame wavelengths with high photometric accuracy and at similar physical scales. Its near-infrared photometric stability {low, constant background} and ability to image large areas of sky at high angular-resolution {compared to adaptive optics} makes HST/NICMOS ideal for this program. Six pointings of NICMOS camera 3 will result in rest-frame optical, high resolution images of 16 confirmed protocluster members, and an additional 60 candidate protocluster members including 29 EROs. These galaxies were selected with a variety of techniques and span a range of projected radii within the protocluster. The proposed observations constitute a unique opportunity to extend the study of galaxies in overdense regions to an early time in cosmic history.

WFPC2 10751

WFPC2 CYCLE 14 Intflat Linearity Check and Filter Rotation Anomaly Monitor

Intflat observations will be taken to provide a linearity check: the linearity test consists of a series of intflats in F555W, in each gain and each shutter. A combination of intflats, visflats, and earthflats will be used to check the repeatability of filter wheel motions. {Intflat sequences tied to decons, visits 1-18 in prop 10363, have been moved to the cycle 14 decon proposal 10744 for easier scheduling.} Note: long-exposure WFPC2 intflats must be scheduled during ACS anneals to prevent stray light from the WFPC2 lamps from contaminating long ACS external exposures.

WFPC2/ACS/WFC 10590

Star-Formation History of an Unmerged Fragment: the Leo A Dwarf Galaxy

The Leo A dwarf irregular is the only known Local Group galaxy that on the weight of current evidence has been suggested to have experienced its first star formation within the past 2-3 billion years. As a galaxy that could have been almost purely gaseous during the epoch of giant galaxy assembly, Leo A is the best nearby candidate to be a redshift zero analogue to the major building blocks of the Milky Way. We propose to obtain deep optical images of Leo A with the ACS/WFC to achieve three main goals: 1} To establish the fractions of star-formation, by mass, that occurred prior and subsequent to the main epoch of hierarchical merging {redshift z ~ 2-4, Age ~ 10-12.5 Gigayears}; 2} to measure the time variation in Leo A’s star-formation rate over the past 10 Gyr, based on statistical analyses of its {V-I, I} color-magnitude diagram; and 3} to measure the radial distributions of young and old stellar populations and quantify the degree to which the optically prominent, young population is embedded in an extended, low-surface brightness sheet or halo of ancient stars. Because of the distance modulus {24.5 mag} and high degree of stellar crowding at the level of the oldest main-sequence turnoffs, the observations necessary to achieve these goals are unobtainable except with HST. The ONLY way to reliably derive the star-formation history of Leo A over its entire lifetime is with photometry to magnitudes of {B, I} = {28.6, 27.9}, the level of the oldest main-sequence turnoff in Leo A. These data would confirm and extend the limited inferences obtained from WFPC2 photometry over 2 magnitudes less deep, and provide the first opportunity to measure the complete star-formation history of a potential “living fossil” analogue to the building blocks of the Milky Way. We propose to use WFPC2 in parallel to measure radial variations in the stellar populations between the galaxy’s core and outskirts. Because the expected 2-gyro jitter ellipse is comparable to the pixel scale of ACS/WFC, we rely on point-spread function fitting photometry, and we require no special scheduling constraints, our proposed program would be virtually unaffected by entry into 2-gyro mode.

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                07                    07
FGS REacq                08                    08
OBAD with Maneuver   31                     31

SIGNIFICANT EVENTS: (None)