Daily #4035

HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT #4035

PERIOD COVERED: UT January 24, 2006 (DOY 024)

OBSERVATIONS SCHEDULED

ACS/HRC 10556

Neutral Gas at Redshift z=0.5

Damped Lyman-alpha systems {DLAs} are used to track the bulk of the
neutral hydrogen gas in the Universe. Prior to HST UV spectroscopy,
they could only be studied from the ground at redshifts z1.65.
However, HST has now permitted us to discover 41 DLAs at z1.65 in our
previous surveys. Followup studies of these systems are providing a
wealth of information about the evolution of the neutral gas phase
component of the Universe. But one problem is that these 41
low-redshift systems are spread over a wide range of redshifts
spanning nearly 70% of the age of the Universe. Consequently, past
surveys for low-redshift DLAs have not been able to offer very good
precision in any small redshift regime. Here we propose an ACS-HRC-
PR200L spectroscopic survey in the redshift interval z=[0.37, 0.7]
which we estimate will permit us to discover another 41 DLAs. This
will not only allow us to double the number of low-redshift DLAs, but
it will also provide a relatively high-precision regime in the
low-redshift Universe that can be used to anchor evolutionary studies.
Fortunately DLAs have high absorption equivalent width, so
ACS-HRC-PR200L has high-enough resoultion to perform this proposed
MgII-selected DLA survey.

ACS/HRC/WFC 10514

Kuiper Belt Binaries: Probes of Early Solar System Evolution

Binaries in the Kuiper Belt are a scientific windfall: in them we have
relatively fragile test particles which can be used as tracers of the
early dynamical evolution of the outer Solar System. We propose a
Snapshot program using the ACS/HRC that has a potential discovery
efficiency an order of magnitude higher than the HST observations that
have already discovered the majority of known transneptunian binaries.
By more than doubling the number of observed objects in dynamically
hot and cold subpopulations we will be able to answer, with
statistical significance, the question of whether these groups differ
in the abundance of binaries as a result of their particular dynamical
paths into the Kuiper Belt. Today's Kuiper Belt bears the imprints of
the final stages of giant-planet building and migration; binaries may
offer some of the best preserved evidence of that long-ago era.

ACS/HRC/WFC 10733

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 6 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 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/WFC 10515

The Unique Star Cluster System of M85

Even with its long history as one of the pillars of modern astronomy,
the study of star clusters has continued to reveal new and surprising
things. Over the past decade, numerous programs with HST have shown
that extragalactic star clusters powerfully probe the processes of
galactic formation, evolution, and destruction. The diversity of star
cluster systems is a testament to the rich variation in galaxy
properties. During the course of the ACS Virgo Cluster Survey, we have
discovered that the early-type galaxy M85 has a system of star
clusters unlike any other galaxy studied to date. Hundreds of star
clusters in M85 are fainter and more extended than typical globular
clusters, and have no local analog. We propose deep optical- infrared
imaging with ACS and NICMOS to obtain ages, metallicities,
luminosities, and sizes of unprecedented precision to characterize
these new star clusters and unravel the evolutionary state of M85 that
gave rise to them.

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 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 10591

ACS Observations of the Galaxies in A Giant Ly-alpha Nebula at z~2.7

Giant Ly-alpha nebulae appear to be sites of ongoing massive galaxy
formation, as evidenced by their association with very luminous,
young, star-forming galaxies and large galaxy overdensities. However
the origin of the extended gas and the source of ionization remain
mysterious. We have discovered a ~200 kpc size nebula which appears to
contain a number of embedded sources, including a very obscured,
luminous mid-infrared source and a Lyman break galaxy. We propose to
obtain deep ACS and NICMOS images of this nebula in order to: {i}
determine the spatial morphology of the Ly-alpha emission on sub-kpc
scales; {ii} precisely locate the known continuum sources within the
nebula; {ii} determine their morphologies; {iii} detect the source of
ionizing photons at the very center of the nebula; {iv} constrain the
ionizing luminosity contributed by a possible distributed population
of faint, compact continuum sources in the nebula; and {v} by SED
fitting of population synthesis models, constrain the ages of the
ionizing sources with the aim of determining the timescale of the
galaxy formation process in the nebula.

ACS/WFC/HRC 10536

What Are Stalled Preplanetary Nebulae? An ACS SNAPshot Survey

Essentially all planetary nebulae {PNs} are aspherical, whereas the
mass-loss envelopes of AGB stars are strikingly spherical. Our
previous SNAPshot surveys of a morphologically unbiased sample of
pre-planetary nebulae {PPNs} -- objects in transition between the AGB
and PN evolutionary phases -- show that roughly half our observed
targets are resolved, with bipolar or multipolar morphologies.
Spectroscopic observations of our sample confirm that these objects
have not yet evolved into planetary nebulae. Thus, the transformation
from spherical to aspherical geometries has already fully developed by
the time these dying stars have become PPNs. Although our current
studies have yielded exciting results, they are limited in two
important ways -- {1} the number of well-resolved objects is still
small {18}, and the variety of morphologies observed relatively
multitudinous, hence no clear trends can yet be established between
morphology and other source properties {e.g., near-IR, far-IR colors,
stellar spectral type, envelope mass}, and {2} the current samples are
strongly biased towards small PPNs, as inferred from their low
60-to-25 micron flux ratios [R{60/25}1]. However, the prototype of
objects with R{60/25}1, the Frosty Leo Nebula, has a puzzlingly large
post-AGB age {almost 10^4 yr} and a fairly cool central star, very
different from the expectations of single-star stellar evolutionary
models. A proposed, but still speculative, hypothesis for such objects
is that the slow evolution of the central star is due to backflow of
material onto the mass-losing star, retarding its evolution towards
the PN phase. This hypothesis has significant consequences for both
stellar and nebular evolution. We therefore propose a survey of PPNs
with R{60/25}1 which is heavily weighted towards the discovery of
such "stalled PPNs". Supporting kinematic observations using long-slit
optical spectroscopy {with the Keck}, millimeter and radio
interferometric observations {with OVRO, VLA & VLBA} are being
undertaken. The results from this survey {together with our previous
work} will allow us to draw general conclusions about the complex
mass-outflow processes affecting late stellar evolution, and will
provide crucial input for theories of post-AGB stellar evolution. Our
survey will produce an archival legacy of long-standing value for
future studies of dying stars.

WFPC2 10501

Extending the Heritage: Clusters, Dust, and Star Formation in M51

Strongly interacting systems in the Local Universe offer the
opportunity to investigate the modality of star formation under
dynamical conditions more typical of the intermediate redshift
Universe {z~0.5-1}, at an exquisite resolution unmatched by distant
galaxies. M51 is one such system. Most recently, the Hubble Heritage
program dedicated 24 HST orbits to obtain a 3X2 ACS mosaic of M51 in
BVI, and Halpha. While this is designed to produce a lovely
multi-color image of this photogenic target, its scientific return
will be limited for star formation studies. Hence we propose to
augment these observations by obtaining WFPC2 U band and NICMOS H band
primary imaging {with NICMOS Paschen alpha in parallel} of selected
pointings of this interacting galaxy system. At the modest cost of 14
additional orbits, we will: {1} accurately determine the ages of the
young star cluster population; {2} secure the identification of 60-70
old globular clusters; {3} search for heavily dust enshrouded stellar
clusters; {4} investigate the distribution of the cluster populations
as a function of location {galactocentric, arms, interarms, etc.}; and
{5} both remove the effects of dust and determine its properties. In
addition to our specific science goals, these observations lend
themselves, on their own or in synergy with data from GALEX and
Spitzer, to a host of other investigations, including those on evolved
diffuse stellar populations, galactic structure, and dust radiative
transfer. We will thus release these data early to the community, by
relinquishing part of the proprietary period.

WFPC2 10745

WFPC2 CYCLE 14 INTERNAL MONITOR

This calibration proposal is the Cycle 14 routine internal monitor for
WFPC2, to be run weekly to monitor the health of the cameras. A
variety of internal exposures are obtained in order to provide a
monitor of the integrity of the CCD camera electronics in both bays
{both gain 7 and gain 15 -- to test stability of gains and bias
levels}, a test for quantum efficiency in the CCDs, and a monitor for
possible buildup of contaminants on the CCD windows. These also
provide raw data for generating annual super-bias reference files for
the calibration pipeline.

FLIGHT OPERATIONS SUMMARY:

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

HSTARS:

10101 - GSAcq (2,3,3) resulted in FLBU (3,0,3) due to Scan Step Limit
Exceeded on FGS 2 @ 025/0401z

GSAcq (2,3,3) scheduled @ 025/04:01:52 results in FLBU (3,0,3) due to
Scan Step Limit Exceeded on FGS 2. OBAD 1: V1 874.25, V2 -110.05, V3
-822.74, RSS 1205.54 OBAD 2: V1 -1.81, V2 -9.94, V3 -1.13, RSS 10.17

COMPLETED OPS REQUEST: (None)

COMPLETED OPS NOTES: (None)

SCHEDULED SUCCESSFUL
FGS GSacq 10 10
FGS REacq 03 03
OBAD with Maneuver 26 26

SIGNIFICANT EVENTS:

Flash Report: TCINIT Adjustment

On DOY 2006/024 at 18:07 GMT, TCINIT was changed from 6 to 7 so that
the EPS FSW will not be reset if six batteries reach charge cut-off.
The system was monitored for one orbit and nominal performance was
observed with five batteries reaching charge cut-off and the maximum
system SOC steady at ~253 Ah. Peak battery temperatures are ~1 degC.