Status Report

NASA Hubble Space Telescope Daily Report # 3767

By SpaceRef Editor
January 4, 2005
Filed under , ,

HUBBLE SPACE TELESCOPE – Continuing to collect World Class Science

DAILY REPORT        # 3767

PERIOD COVERED: DOYs 365 (2004) -002 (2005)

OBSERVATIONS SCHEDULED

NIC3 9846

The Origins of Sub-stellar Masses: Searching for the End of the IMF

Is there a preferred scale that defines the end of the IMF? We propose
to test this hypothesis by conducting a deep spectroscopic survey of
extremely low mass objects in the embedded young cluster associated
with NGC1333. At a distance of only 300pc, this cluster is one of the
nearest examples of a dense young cluster. We will be able to obtain
R=200 spectra and photometry for 40-60 cluster members with masses
between 5-40 Jupiter masses at an age of 1 Myr observed through
A{v}<10 mag. This will enable us to estimate temperatures and luminosities for all sources detected in the survey. We will compare their positions in an H-R diagram to PMS evolutionary tracks in order to estimate their ages and masses. For a solar metallicity cloud at a temperature of 10 K, the minimum mass for fragmentation is thought to be 10 Jupiter masses. A statistically significant sample of objects detected below this limit would challenge the role of hierarchical fragmentation in limiting substellar masses. The proximity of this cluster combined with the unique sensitivity, wavelength coverage, and multi-object spectroscopic capability of NICMOS on HST make this experiment possible.

NICMOS 8790

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.

ACS/HRC 10435

Merger-Induced Populations in Early-Type Galaxy Cores

Hierarchical formation models predict that early-type galaxies are
built up over an extended period from mergers of smaller systems, a
process which should leave long-lived signatures in their light
profiles and stellar population colors. Merger events should have
continued up to relatively recent times {the last 1-5 Gyr}, and many
ellipticals and S0 bulges should therefore show evidence of multiple,
discrete, intermediate-age populations. Although there is substantial
observational support for a dissipational merger origin for some
early- type galaxies, most do not exhibit the expected anomalies in
either their light profiles or color distributions. However, existing
searches {mainly in the V and I bands} have not probed very deeply.
Here we propose high resolution, broad-band, near-ultraviolet
{2500-3400 A} imaging of the cores of bright early-type galaxies. This
is the most sensitive probe available for the detection of
spatially-segregated, multiple population components with ages in the
range 1-5 Gyr. Our sample consists of dust- and AGN-free systems with
both normal and mildly anomalous central light profiles. There is very
little existing information on the near-UV structure of early-type
galaxies, and our program would effectively explore new terrain.

ACS/WFC/WFPC2 10402

The Formation and Evolution of Spirals: An ACS and WFPC2 Imaging
Survey of Nearby Galaxies

Over 50% of galaxies in the local universe are spirals. Yet the star
formation histories and evolution of this crucial population remain
poorly understood. We propose to combine archival data with new
ACS/WFC and WFPC2 observations of 11 galaxies, to tackle a
comprehensive investigation of nearby spirals covering the entire
spiral sequence. The new observations will fill a serious deficiency
in HST’s legacy, and maximize the scientific return of existing HST
data. The filter combination of UBVI, and Halpha is ideal for studying
stellar populations, dust properties, and the ISM. Our immediate
scientific objectives are: {i} to use the resolved cluster
populations, both young massive clusters and ancient globular clusters
as a chronometer, to understand how spirals assembled as a function of
time; {ii} study the rapid disruption properties of young clusters;
and {iii} understand dust distributions in spirals from pc to kpc
scales. Each of these goals provides an important step towards
charting the evolution of galaxies, and an essential baseline for
interpreting the galaxy populations being surveyed in both the early
and present universe. The resolution of our survey, which exploits the
excellent imaging capabilities of HST’s two optical cameras, will
enable us to understand the record of star cluster, and galaxy
formation in a level of detail which is not possible for more distant
systems. Finally, the proposed observations will provide a key to
interpret an extensive, multiwavelength archive of space- and ground-
based data at lower spatial resolution {SPITZER, CHANDRA, GALEX,
NICMOS P alpha and H band imaging} for local spirals.

NIC1/Spacecraft 10382

NICMOS Focus Stability

The purpose of this activity is to determine the best focus. This
program will execute in one month intervals starting about 1 month
after the last execution of proposal 9994 {the previous focus
monitoring program}. The program starts with a focus sweep using only
the NIC1 camera {visit 11}. The following observation is with the NIC2
camera {visit 12} after about 45 days. This pattern is repeated
throughout the period except for Feb 15 where also the NIC3 camera is
used. In total this will result in 9 orbits. Notice that VISIT #1 #2
refers to visits for #1 sequential visit number for a given camera #2
camera in question visit 32 is therefore the third visit for camera 2.

NIC1/NIC2/NIC3 10379

Flats Stability

This calibration proposal is the Cycle 13 NICMOS flat field monitor
program. A series of camera 1, 2, & 3 flat fields will be obtained to
monitor the health of the cameras.

ACS/HRC/WFC 10370

CCD Hot Pixel Annealing

Hot pixel annealing will continue to be performed once every 4 weeks.
The CCD TECs will be turned off and heaters will be activated to bring
the detector temperatures to about +20C. This state will be held for
approximately 12 hours, after which the heaters are turned off, the
TECs turned on, and the CCDs returned to normal operating condition.
To assess the effectiveness of the annealing, a bias and four dark
images will be taken before and after the annealing procedure for both
WFC and HRC. The HRC darks are taken in parallel with the WFC darks.
The charge transfer efficiency {CTE} of the ACS CCD detectors declines
as damage due to on-orbit radiation exposure accumulates. This
degradation has been closely monitored at regular intervals, because
it is likely to determine the useful lifetime of the CCDs. We will now
combine the annealling activity with the charge transfer efficiency
monitoring and also merge into the routine dark image collection. To
this end, the CTE monitoring exposures have been moved into this
proposal . All the data for this program is acquired using internal
targets {lamps} only, so all of the exposures should be taken during
Earth occultation time {but not during SAA passages}. This program
emulates the ACS pre-flight ground calibration and post- launch SMOV
testing {program 8948}, so that results from each epoch can be
directly compared. Extended Pixel Edge Response {EPER} and First Pixel
Response {FPR} data will be obtained over a range of signal levels for
both the Wide Field Channel {WFC}, and the High Resolution Channel
{HRC}.

ACS/HRC/WFC 10367

ACS CCDs daily monitor- cycle 13 – part 1

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.

WFPC2 10363

WFPC2 CYCLE 13 Intflat and Visflat Sweeps and Filter Rotation Anomaly
Monitor

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 in the event of complete failure of the visflat lamp
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.

ACS/WFC 10361

Earth Flats

This proposal monitors flatfield stability. This proposal obtains
sequences of Earth streak flats to construct high quality flat fields
for the WFPC2 filter set. These flat fields will allow mapping of the
OTA illumination pattern and will be used in conjunction with previous
internal and external flats to generate new pipeline superflats. These
Earth flats will complement the Earth flat data obtained during cycles
4-12.

ACS/WFC/WFPC2 10265

The Formation History of Andromeda

We propose deep observations of Andromeda’s outer disk and giant tidal
stream, to reconstruct their star formation histories. As the nearest
giant galaxy, Andromeda offers the best testing ground for
understanding galaxy formation and evolution. Given the dramatic
increase in sensitivity offered by the ACS, we can now resolve stars
on the old main sequence in the other giant spiral of the Local Group,
and employ the same direct age diagnostics that have been used for
decades in the study of Galactic globular clusters. In Cycle 11, we
successfully observed a field in the Andromeda halo and constructed a
deep color-magnitude diagram reaching well below the oldest main
sequence turnoff. In Cycle 13, we propose to extend these observations
to the outer disk and tidal stream of Andromeda, to constrain their
star formation histories and compare them to that of the halo. The
combined observations from these two programs will offer a dramatic
advance in our understanding of the overall evolution of spiral
galaxies.

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 10201

The Origin of Dwarf Galaxies and Steep Luminosity Functions in
Clusters

Clusters of galaxies contain an over density of dwarfs compared to the
field. The origin of these dwarfs is unknown, but a large fraction of
them did not form through standard collapses early in the universe.
Some dwarf ellipticals in clusters have metal rich and young stellar
populations while others contain old metal poor populations,
suggesting multiple formation mechanisms and time scales. We propose
to test the idea that dwarfs descend from galaxies accreted into
clusters during the past 8 Gyrs by correlating ages and metallicities
of dwarfs with their internal structures – spiral arms, bars, and
disks. If dwarfs originate from more massive galaxies then these
features should be common in metal rich and young dwarfs. On the other
hand, if no correlation is found it would suggest that dwarfs form
through in-situ collapses of gas in the intragalactic medium after the
universe was reionized.

ACS/HRC 10199

The Most Massive Galaxies in the Universe: Double Trouble?

We are proposing an HST snapshot survey of 70 objects with velocity
dispersion larger than 350 km/s, selected from the Sloan Digital Sky
Survey. Potentially this sample contains the most massive galaxies in
the Universe. Some of these objects may be superpositions; HST imaging
is the key to determining if they are single and massive or if they
are two objects in projection. The objects which HST imaging shows to
be single objects are interesting because they potentially harbor the
most massive black holes, and because their existence places strong
constraints on galaxy formation models. When combined with ground
based data already in hand, the objects which HST imaging shows are
superpositions provide valuable information about interaction rates of
early-type galaxies as well as their dust content. They also constrain
the allowed parameter space for models of binary gravitational lenses
{such models are currently invoked to explain discrepancies in the
distribution of lensed image flux ratios and separations}.

ACS/WFC/NIC3 10195

Probing the Surroundings of a Highly Luminous Redshift 6.5 Galaxy

We propose deep images of a recently discovered galaxy at z=6.535,
which is among the most luminous Lyman-alpha emitting galaxies known
at high redshift. The brightness and rarity of this source imply that
it is associated with a high peak in the matter density distribution.
{It is the brightest Lyman alpha source in 2e5 comoving Mpc3, with a
luminosity of 6 L*.} Further objects in this peak are expected to be
visible with HST’s sensitivity. The Lyman alpha line has a large rest
frame equivalent width, with a lower bound >100 Angstroms. Such a
large equivalent width would be impossible for objects embedded in
neutral gas, and instead requires either that {a} the universe was
reionized before z=6.5 or {b} the galaxy resides in a local ionized
bubble, in which case an additional contribution to the ionizing
photon budget from presently undetected neighbors is required. With 19
orbits of ACS and NICMOS imaging, we will measure this object’s
morphology and spectral energy distribution, thus searching for either
active nuclei or old stellar populations. We will also search for
possible neighbors, which could establish the first known galaxy group
at z>6, and may provide sufficient ionizing flux to allow the escape
of the observed Lyman alpha photons in a neutral universe. If
neighbors are not found, it will lead to an upper bound on the neutral
fraction in the general IGM at z=6.5.

ACS/WFC 10178

Imaging Polarimetry of Young Stellar Objects with ACS and NICMOS: A
study in dust grain evolution

The formation of planetary systems is intimately linked to the dust
population in circumstellar disks, thus understanding dust grain
evolution is essential to advancing our understanding of how planets
form. By combining {1} the high resolution polarimetric capabilities
of ACS and NICMOS, {2} powerful 3-D radiative transfer codes, and {3}
observations of objects known to span the earliest stellar
evolutionary phases, we will gain crucial insight into the initial
phases of dust grain growth: evolution away from an ISM distribution.
Fractional polarization is a strong function of wavelength, therefore
by comparing polarimetric images in the optical and infrared, we can
sensitively constrain not only the geometry and optical depth of the
scattering medium, but also the grain size distribution. By observing
objects representative of the earliest evolutionary sequence of YSOs,
we will be able to investigate how the dust population evolves in size
and distribution during the crucial transition from a disk+envelope
system to a disk+star system. The proposed study will help to
establish the fundamental time scales for the initial depletion of
ISM-like grains: the first step in understanding the transformation
from small submicron sized dust grains, to large millimeter sized
grains, and untimely to planetary bodies.

NIC2 10177

Solar Systems In Formation: A NICMOS Coronagraphic Survey of
Protoplanetary and Debris Disks

Until recently, despite decades of concerted effort applied to
understanding the formation processes that gave birth to our solar
system, the detailed morphology of circumstellar material that must
eventually form planets has been virtually impossible to discern. The
advent of high contrast, coronagraphic imaging as implemented with the
instruments aboard HST has dramatically enhanced our understanding of
natal planetary system formation. Even so, only a handful of evolved
disks {~ 1 Myr and older} have been imaged and spatially resolved in
light scattered from their constituent grains. To elucidate the
physical processes and properties in potentially planet-forming
circumstellar disks, and to understand the nature and evolution of
their grains, a larger spatially resolved and photometrically reliable
sample of such systems must be observed. Thus, we propose a highly
sensitive circumstellar disk imaging survey of a well-defined and
carefully selected sample of YSOs {1-10 Myr T Tau and HAeBe stars} and
{> app 10 Myr} main sequence stars, to probe the posited epoch of
planetary system formation, and to provide this critically needed
imagery. Our resolved images will shed light on the spatial
distributions of the dust in these thermally emissive disks. In
combination with their long wavelength SEDs the physical properties of
the grains will be discerned, or constrained by our photometrically
accurate surface brightness sensitivity limits for faint disks which
elude detection. Our sample builds on the success of the exploratory
GTO 7233 program, using two-roll per orbit PSF-subtracted NICMOS
coronagraphy to provide the highest detection sensitivity to the
smallest disks around bright stars which can be imaged with HST. Our
sample will discriminate between proposed evolutionary scenarios while
providing a legacy of cataloged morphologies for interpreting mid- and
far-IR SEDs that the recently launched Spitzer Space Telescope will
deliver.

NIC2 10173

Infrared Snapshots of 3CR Radio Galaxies

Radio galaxies are an important class of extragalactic objects: they
are one of the most energetic astrophysical phenomena and they provide
an exceptional probe of the evolving Universe, lying typically in high
density regions but well-represented across a wide redshift range. In
earlier Cycles we carried out extensive HST observations of the 3CR
sources in order to acquire a complete and quantitative inventory of
the structure, contents and evolution of these important objects.
Amongst the results, we discovered new optical jets, dust lanes,
face-on disks with optical jets, and revealed point-like nuclei whose
properties support FR-I/BL Lac unified schemes. Here, we propose to
obtain NICMOS infrared images of 3CR sources with z<0.3 as a major enhancement to an already superb dataset. We aim to deshroud dusty galaxies, study the underlying host galaxy free from the distorting effects of dust, locate hidden regions of star formation and establish the physical characteristics of the dust itself. We will measure frequency and spectral energy distributions of point-like nuclei, expected to be stronger and more prevalent in the IR, seek spectral turnovers in known synchrotron jets and find new jets. We will strongly test unified AGN schemes and merge these data with existing X-ray to radio observations. The resulting database will be an incredibly valuable resource to the astronomical community for years to come.

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.

ACS/WFC/NIC3/WFPC2 10134

The Evolution and Assembly of Galactic Disks: Integrated studies of
mass, stars and gas in the Extended Groth Strip

This project is a 126-orbit imaging survey in F606W/F814W ACS to
measure the evolution of galaxy disks from redshift z = 1.4 to the
present. By combining HST imaging with existing observations in the
Extended Groth Strip, we can for the first time simultaneously
determine the mass in dark matter that underlies disks, the mass in
stars within those disks, and the rate of formation of new stars from
gas in the disks, for samples of >1, 000 objects. ACS observations are
critical for this work, both for reliable identifications of disks and
for determining their sizes and inclinations. Combining these data
with the kinematics measured from high- resolution Keck DEIMOS spectra
will give dynamical masses that include dark matter. Stellar masses
can be measured separately using ground-based BRIK and Spitzer IRAC
GTO data, while cross-calibrated star formation rates will come from
DEEP2 spectra, GALEX, and Spitzer/MIPS. The field chosen is the only
one where all multiwavelength data needed will be available in the
near term. These data will show how the fundamental properties of
disks {luminosity, rotation speed, scale length} and their scaling
relations have evolved since z~1, and also will measure the build-up
of stellar disks directly, providing fundamental tests of disk
formation and evolution. In addition to the above study of disk
galaxies, the data will also be used to measure the evolution of
red-sequence galaxies and their associated stellar populations. ACS
images will yield the number of red-sequence galaxies versus time,
together with their total associated stellar mass. ACS images are
crucial to classify red-sequence galaxies into normal E/S0s versus
peculiar types and to measure radii, which will complete the suite of
fundamental structural parameters needed to study evolution. We will
measure the zeropoints of major scaling laws {Fundamental Plane,
radius versus sigma}, as well as evolution in characteristic
quantities such as L*, v*, and r*. Stellar population ages will be
estimated from high-resolution Keck DEIMOS spectra and compared to SED
evolution measured from GALEX, HST, Spitzer, and ground-based colors.
Important for both disk and red-galaxy programs are parallel exposures
to be taken with both NIC3 {J and H} and WFPC2 {B}. These are arranged
so that ACS, WFPC2, and NIC3 all overlap where possible , providing a
rich data set of galaxies imaged with all three HST cameras from B to
H. These data will be used to measure restframe visible morphologies
and UV star-formation rates for galaxies near the edge of the survey,
to discover and count EROs below the Keck spectroscopic limit of R =
24, and to provide an improved database of photometric redshifts for
galaxies in the overlap regions.

WFPC2 10132

UV Confirmation of New Quasar Sightlines Suitable for the Study of
Intergalactic Helium

The reionization of intergalactic helium is thought to have occurred
between redshifts of about 3 and 4. The study of HeII Lyman-alpha
absorption towards a half-dozen quasars at 2.72.9 SDSS quasars, but with special
emphasis on extending helium studies to the highest redshift
sightlines. Our proposed approach has already proven successful, and
additional sightlines will enable follow-up spectal observations to
measure the spectrum and evolution of the ionizing background
radiation, the density of intergalactic baryons, and the epoch of
reionization of the IGM.

ACS/WFC/NIC3 10127

Imaging a protocluster at z=3.1: Effects of environment and evolution
on galaxy populations in the early universe

We propose imaging a rich protocluster, 0316-26 at z = 3.13, with 31
confirmed Lya cluster members. The bright radio galaxy host is
identified with the progenitor of the dominant cluster galaxy. Because
its redshift places Lya into an ACS narrow-band filter, the
protocluster provides a unique laboratory for studying galaxies at a
crucial epoch in the evolution of the Universe. We shall {i} measure
and compare sizes, morphologies and colors of galaxies from
populations detected using 4 different selection techniques {Lyman and
4000A breaks, Lya and [OIII] excesses}, {ii} study effects of an
overdense environment by comparing the properties of protocluster
galaxies with z~3 field galaxies from GOODS, {iii} study effects of
evolution by relating our data to observations of similar
protocluster/cluster targets at redshifts z = 4.1, 2.2, and 1.2, and
{iv} constrain the formation of the most massive cluster galaxies by
investigating the spatial distribution, Lya equivalent widths and
other properties within the 5″ radio galaxy host. The ultimate aim is
to disentangle the history of structure development and stellar
evolution for rich clusters of galaxies.

FGS 10106

An Astrometric Calibration of the Cepheid Period-Luminosity Relation

We propose to measure the parallaxes of 10 Galactic Cepheid variables.
When these parallaxes {with 1-sigma precisions of 10% or better} are
added to our recent HST FGS parallax determination of delta Cep
{Benedict et al 2002}, we anticipate determining the Period-Luminosity
relation zero point with a 0.03 mag precision. In addition to
permitting the test of assumptions that enter into other Cepheid
distance determination techniques, this calibration will reintroduce
Galactic Cepheids as a fundamental step in the extragalactic distance
scale ladder. A Period-Luminosity relation derived from solar
metallicity Cepheids can be applied directly to extragalactic solar
metallicity Cepheids, removing the need to bridge with the Large
Magellanic Cloud and its associated metallicity complications.

ACS/HRC/WFC 10105

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 10006

Black Hole X-ray Novae in M31

During A01-3 we found 22 Black Hole X-ray Novae {BHXN} in M31 using
Chandra, and with HST {WFPC2} found two optical counterparts. Our
results suggest either a surprisingly high ratio of BH to NS binaries,
or a surprisingly high duty cycle for BHXN. We propose to continue
this program, with the goals of understanding the relative number of
BH vs. NS X-ray binaries in the M31 bulge, and determining the orbital
period distribution and duty cycles of these BHXN. Continued
observations can determine the duty cycle. The new ACS will allow us
to go 2 mags deeper than the WFPC2, and could triple the number of
optical counterparts and therefore orbital period estimates. M31 is
the only galaxy near enough to allow this extragalactic survey for
BHXN.

FLIGHT OPERATIONS SUMMARY:

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

HSTAR 9638: FHST Updates (U2,3RD) @ 001/20:42:49Z resulted in Error
Box failure indicating “2 FAILED”. One 486 Status Buffer 901 message
received. Update followed Astrometry session. Under investigation.

HSTAR 9639: FHST Updates (U2,3FM) @ 001/16:09:46Z resulted in Error
Box failure indicating “2 FAILED”. One 486 Status Buffer 901 message
received. FM Update directly following it passed along with the GS
Acquisition. Under investigation.

HSTAR 9640: During LOS, GS Acquisition @ 002/23:04:34Z resulted in FL
backup (2,0,2) using FGS 2. The two FM Updates @ 002/22:55:23Z and
22:58:08Z, prior to the GS Acquisition, both succeeded and had a very
low vehicle error observed. Subsequent FHST Map @ 002/23:09:09Z
showed axis errors of -15.422, -4.226, and -1.610 arcsec. Under
investigation.

COMPLETED OPS REQs:

17357-0 Dump ACS EDAC RAM @365/1729Z

OPS NOTES EXECUTED: None

                    SCHEDULED     SUCCESSFUL    FAILURE TIMES
FGS Gsacq             37             37
FGS Reacq             26             26
FHST Update           57             55        001/2043z (HSTAR#9638) 
002/1611z (HSTAR#9639)
LOSS of LOCK

SIGNIFICANT EVENTS:

ACS successfully intercepted the Science Timeline on December 30,
following recovery from Suspend mode. All data look nominal and ACS is
successfully functioning in Operate mode without any problems.

SpaceRef staff editor.