Status Report

NASA Hubble Space Telescope Daily Status Report #3861

By SpaceRef Editor
May 17, 2005
Filed under , ,

HUBBLE SPACE TELESCOPE – Continuing to collect World Class Science




ACS/HRC 10165

Determination of orbits and colors for two new binaries in the Koronis
asteroid family

We propose to measure color and orbital properties of two asteroid
binaries in the Koronis family discovered in our SNAP-9747 survey. The
best previously studied asteroid binary system, Ida/Dactyl, is also in
the Koronis family. Differential space weathering measured on the Ida
and Dactyl surfaces has been a powerful constraint on models of
satellite formation mechanisms and satellite survivability. HST offers
the unique opportunity for similar measurements of these much smaller,
main-belt binaries. The new satellites are believed to have formed
through different collisional mechanisms than Ida/Dactyl. Further,
with a set of 4 relative position measurements for each of the two
systems, added to the discovery snapshots, we will determine and
compare the densities of the primaries with Ida {a large, 31.5 km,
asteroid with density 2.6+-0.5 g/cm^3, measured by the Galileo flyby}.
In contrast, {17246} and {22899} are 4.5 km bodies that are likely to
have been restructured since the family-forming event by subsequent
collisions. As all are members of the same family, differences in
density would constrain bulk composition and internal structure {e.g.
shard vs. rubble-pile}. Hence, these measurements are likely to
further elucidate the mechanisms for formation of satellites.

ACS/HRC 10255

A Never Before Explored Phase Space: Resolving Close White Dwarf / Red
Dwarf Binaries We propose an ACS Snapshot imaging survey to resolve a
well-defined sample of highly probable white dwarf plus red dwarf
close binaries. These candidates were selected from a search for white
dwarfs with infrared excess from the 2MASS database. They represent
unresolved systems {separations less than approximately 2″ in the
2MASS images} and are distributed over the whole sky. Our HST+ACS
observations will be sensitive to a separation range {1-20 AU} never
before probed by any means. The proposed study will be the first
empirical test of binary star parameters in the post-AGB phase, and
cannot be accomplished from the ground. By resolving as few as 20 of
our ~100 targets with HST, we will be able to characterize the
distribution of orbital semi-major axes and secondary star masses.

ACS/HRC 10377

ACS Earth Flats

High signal sky flats will be obtained by observing the bright Earth
with the HRC and WFC. These observations will be used to verify the
accuracy of the flats currently used by the pipeline and will provide
a comparison with flats derived via other techniques: L-flats from
stellar observations, sky flats from stacked GO observations, and
internal flats using the calibration lamps. Weekly coronagraphic
monitoring is required to assess the changing position of the spots.


ACS CCDs daily monitor – Cycle 13 – Part 2

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.

ACS/WFC 10187

Direct imaging of the progenitors of massive, core-collapse supernovae

Modern supernovae searches in the nearby Universe are discovering
large numbers of SNe which have massive star progenitors {Types II, Ib
and Ic}. The extensive HST image archives of galaxies within ~20Mpc
enables their individual bright stellar content to be resolved. As
massive, evolved stars are the most luminous single objects in a
galaxy, the progenitors of core-collapse SNe should be directly
detectable on pre-explosion images. In our ongoing HST programme we
have detected the first red supergiant progenitor of a normal type II
supernova, shown that SN 1993J came from a binary system, and set
direct mass-limits on three other type II supernovae progenitors.
These discoveries are providing strong constraints on theoretical
models of pre-supernova stellar evolution that predict which stars
produce which type of supernovae. We request time to continue this
successful project, and require ACS observations of future SNe which
are discovered in galaxies closer than 20Mpc which have pre-explosion
HST archive images available. These observations will allow the SNe to
be precisely positioned on the pre-explosion frames with the required
astrometric accuracy of around 0.05″, and provide 3-colour photometry
of the surrounding stellar populations for reddening estimations. The
goal of this project is to directly identify the progenitor stars of
core-collapse supernovae. We will compare the results to our own
stellar evolutionary tracks in order to determine masses or
restrictive mass-limits for the progenitors.

ACS/WFC 10237

Low-Ionization BALs: Evolution or Orientation?

We propose to test the hypothesis that Low-Ionization Broad Absorption
Line Quasars {LoBALs} represent a special stage of quasar evolution:
young quasars in systems with strong interaction and star-formation.
We will carry out high resolution imaging using ACS/WFC and NICMOS to
measure the properties of the host galaxies of four LoBAL quasars at z
= 0.9 – 2.0 that show strong overlapping FeII absorption troughs. The
ACS imaging will be carried out in the passband with the strongest BAL
absorption, acting as a natural coronagraph. This results in a
reduction of quasar light by a factor of 15 – 26 in these passbands,
providing arguably the best view of the host galaxies of luminous,
high-redshift quasars. This method allows efficient detection and
detailed modeling of the host galaxy morphology in the rest-frame
ultraviolet, which is most sensitive to star formation and galaxy
interaction. We will also use NICMOS imaging to measure the rest-
frame light from the host galaxy to probe the old stellar populations
where the host galaxy is likely to be brighter. It has been suggested
that LoBALs might not be explained simply as an orientation effect but
rather as an early phase of quasar evolution. Such a phase is
typically associated with large amounts of dust and gas, and young
galaxies with strong star formation. With HST observations, we will
study the color and morphology of the FeLoBAL quasar host galaxies,
and measure the age of their dominant stellar populations. We will
also measure the density of close companions, and, in particular, look
for signs of ongoing or recent mergers. These measurements will be
compared to those of control samples of normal quasars at similar
redshift. If LoBALs are indeed young systems, then their host galaxies
are expected to show stronger interactions and merger activity,
younger stellar ages, and regions with strong star formation. If the
LoBAL host galaxies show no significant difference from those of
normal quasars, it will support the view that LoBAL quasars are not a
distinct population and that all quasars have BAL outflows along some
lines of sight.

ACS/WFC 10417

Host Galaxies and Environments of the Most Massive Black Holes in the
Early Universe

The existence of luminous quasars with billion solar mass black holes
at high redshift poses important questions about the relation between
the formation and evolution of the earliest galaxies and quasars in
the universe: how could these high- redshift black holes accrete
matter so quickly and so efficiently? Is the quasar phase connected to
the formation of galactic bulge in the earliest epoch? Was the black
hole-bulge mass relation observed locally already established at
high-redshift? We will use ACS/WFC to obtain rest-frame UV imaging of
five quasars at z~4 with the highest estimated black hole mass, of the
order 10 billion solar masses. The goal of the HST observation is to
directly detect their host galaxies and to probe their galactic
environment. These quasars are likely among the most massive and
luminous host galaxies at high-redshift, providing ideal targets for
direct detection. The rest-frame UV properties measured with HST will
be combined with rest-frame optical, mid to far-IR oberservations of
these quasars to measure the star-formation rate, to estimate the
stellar age and mass of the host galaxy, and to probe the
quasar/starburst connection, quasar triggering mechanism and relation
between black hole and bulge formation at the highest possible
redshift. One of the targets, PSS 2322+1944 {z=4.17}, is a
gravitational lensed quasar with a nearly complete Einstein ring in CO
emission, providing a unique opportunity to study the small scale
structure of a high-redshift quasar host galaxy.

ACS/WFC/NIC2 10189

PANS-Probing Acceleration Now with Supernovae

Type Ia supernovae {SNe Ia} provide the most direct evidence for an
accelerating Universe, a result widely attributed to dark energy.
Using HST in Cycle 11 we extended the Hubble diagram with 6 of the 7
highest-redshift SNe Ia known, all at z>1.25, providing conclusive
evidence of an earlier epoch of cosmic deceleration. The full sample
of 16 new SNe Ia match the cosmic concordance model and are
inconsistent with a simple model of evolution or dust as alternatives
to dark energy. Understanding dark energy may be the biggest current
challenge to cosmology and particle physics. To understand the nature
of dark energy, we seek to measure its two most fundamental
properties: its evolution {i.e., dw/dz}, and its recent equation of
state {i.e., w{z=0}}. SNe Ia at z>1, beyond the reach of the ground
but squarely within the reach of HST with ACS, are crucial to break
the degeneracy in the measurements of these two basic aspects of dark
energy. The SNe Ia we have discovered and measured with HST in Cycle
11, now double the precision of our knowledge of both properties. Here
we propose to quadruple the sample of SNe Ia at z>1 in the next two
cycles, complementing on-going surveys from the ground at z<1, and again doubling the precision of dark energy constraints. Should the current best fit model prove to be the correct one, the precision expected from the current proposal will suffice to rule out a cosmological constant at the 99% confidence level. Whatever the result, these objects will provide the basis with which to extend our empirical knowledge of this newly discovered and dominant component of the Universe, and will remain one of the most significant legacies of HST. In addition, our survey and follow-up data will greatly enhance the value of the archival data within the target Treasury fields for galaxy studies.

NIC1 10143

Ultracool companions to the nearest L dwarfs

We propose to conduct the most sensitive survey to date for low mass
companions to nearby L dwarfs. We will use NICMOS to image targets
drawn from a volume- complete sample of 70 L dwarfs within 20 parsecs.
The combination of infrared imaging and proximity will allow us to
search for T dwarf companions at separations as small as 1.6 AU. This
is crucial, since no ultracool binaries are currently known with
separations exceeding 15 AU. Only 10 dwarfs in this sample have
previous HST observations primarily at optical wavelengths. With the
increased sensitivity of our survey, we will provide the most
stringent test to date of brown dwarf models which envisage formation
as ejected stellar embryos. In addition, our observations will be
capable of detecting binaries with mass ratios as low as 0.3, and will
therefore also test the apparent preference for equal-mass ultracool
binaries. Finally, our observations offer the best prospect to date of
detecting companions significantly cooler than the coolest t dwarf
currently known.

NIC2 10418

Morphologies and Color Gradients of Galaxies with the Oldest Stellar
Populations at High Redshifts

We have isolated a sample of 9 luminous {~2L*} galaxies with the very
oldest stellar populations at their respective redshifts. The galaxies
have been found in radio- source fields chosen to be at the key
redshifts z~1.5 and z~2.5, which allow the cleanest separation of old
stellar populations from highly reddened starbursts with colors
derived from standard filter combinations. Ground-based observations
in excellent seeing and with adaptive optics of 3 of these galaxies
indicate that all 3 are dominated by well relaxed disks of old stars,
suggesting that the first large stellar systems to form in the
universe were disks in which star formation proceeded extremely
rapidly and efficiently. In order to test this conjecture, we are
requesting NICMOS2 exposures of our sample to obtain high S/N imaging
in the F160W filter to determine detailed morphologies of the old
stellar population, coupled with either NICMOS2 F110W or ACS F814W
exposures {depending on redshift} to determine color gradients and/or
other systematic color variations that might provide clues to
formation processes.


NICMOS Post-SAA calibration – CR Persistence Part 1.

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.

WFPC2 10359

WFPC2 CYCLE 13 Standard Darks

This dark calibration program obtains dark frames every week in order
to provide data for the ongoing calibration of the CCD dark current
rate, and to monitor and characterize the evolution of hot pixels.
Over an extended period these data will also provide a monitor of
radiation damage to the CCDs.

WFPC2 10363

WFPC2 CYCLE 13 Intflat and Visflat Sweeps and Filter Rotation Anomaly

Using intflat observations, this WFPC2 proposal is designed to monitor
the pixel-to- pixel flatfield response and provide a linearity check.
The intflat sequences, to be done once during the year, are similar to
those from the Cycle 12 program 10075. The images will provide a
backup database as well as allow monitoring of the gain ratios. The
sweep is a complete set of internal flats, cycling through both
shutter blades and both gains. The linearity test consists of a series
of intflats in F555W, in each gain and each shutter. As in Cycle 12,
we plan to continue to take extra visflat, intflat, and earthflat
exposures to test the repeatability of filter wheel motions.


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

HSTARS: (None)



 FGS Gsacq          6             6 
 FGS Reacq         10            10 
 FHST Update       12            12 


SpaceRef staff editor.