Daily #4018

HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT #4018

PERIOD COVERED: UT December 29, 2005 (DOY 363)

OBSERVATIONS SCHEDULED

ACS/HRC 10602

A Complete Multiplicity Survey of Galactic O2/O3/O3.5 Stars with ACS

Massive stars are preferentially formed in compact multiple systems
and clusters and many of them remain spatially unresolved to date,
even in our Galaxy. This has hindered the determination of the stellar
upper mass limit. The lack of an accurate knowledge of the
multiplicity of massive stars can also introduce biases in the
calculation of the IMF at its high-mass end. We have recently used
ACS/HRC to resolve HD 93129 A, the earliest O-type star known in the
Galaxy, into a 55 mas binary. We propose here to extend that work into
a complete multi-filter ACS imaging survey of all {20} known
O2/O3/O3.5 Galactic stars to characterize the multiplicity of the most
massive stars. The data will be combined with existing FGS
observations to explore as large a parameter range as possible and to
check for consistency. We will also derive the IMF of each system
using a crowded-field photometry package and processing the data with
CHORIZOS, a code that can derive stellar temperatures, extinctions,
and extinction laws from multicolor photometry.

ACS/HRC/WFC 10575

Lyman alpha morphology of local starburst galaxies

Our pilot imaging study of 6 local galaxies using ACS/SBC in the
cosmologically important Lyman- alpha line has begun to reveal
intriguing results. Here we propse ACS/HRC imaging of this sample, the
approval of the which will allow for a significant increase in the
impact of the original study and extend the limits of current
understanding of Lyman-alpha escape. With this data we can accurately
calibrate our Lyman-alpha line-only images and explore for the first
time Lyman- alpha fluxes and equivalent widths in spatially resolved
systems. These data would also allow us to test the current models of
Lyman-alpha escape mechanisms and investigate possible correlations
between Lyman-alpha emission and other local parameters such as age
and internal reddening. The addition of high-resolution H-alpha data
allows us to quantitatively study the decoupling of Lyman-alpha from
non-resonant radiation and spatially explore the destruction and
attenuation of Lyman-alpha. The study will go a long way towards
resolving the outstanding issues complicating the interpretation of
high redshift studies and the use of Lyman-alpha to quantitatively
study the distant universe.

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 10574

Witnessing Galaxy Transformation in Galaxy Groups at z 1

The recent discover of five galaxy groups in the Lynx supercluster
region offers us the exciting opportunity to observe for the first
time groups in the process of collapsing into a merging pair of
clusters at z 1. Our current picture of structure formation suggests
that substantial evolution of galaxy properties can occur in groups
and filaments well before they enter the environs of massive clusters.
However, neither current theoretical models nor observations give us a
complete understanding of the relative importance of the different
physical processes that control the structural and spectral
transformations that occur prior to, during, and after infall into a
dense environment. We propose direct observation of these newly
discovered dynamically young structures in the Lynx region, in order
to provide a critical benchmark in testing not only whether galaxy
evolution occurs mostly prior to entry into the densest regions but
will also constrain the relative importance of initial conditions in
determining the fate of galaxy systems. Our analysis of these proposed
ACS measurements will be complemented with an unique dataset we have
already in the optical, infrared, mid-infrared, and X-ray.

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.

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.

WFPC2 10608

Probing the star formation law in the extreme outer limits of M83, a
prototypical XUV-disk galaxy

The Galaxy Evolution Explorer {GALEX} has discovered a new sub-class
of spiral galaxy, which we refer to as extended UV-disk {XUV-disk}
galaxies. They are distinguished by conspicuous UV-bright star
clusters located at galactocentric radii extending to many times the
optical {R25} extent, and appear to represent a population of spiral
galaxies still actively building, or augmenting, their stellar disk.
However, XUV-disks pose a mystery in the form of a relative lack of
HII regions {traced by H-alpha emission} associated with outer disk,
UV-bright stellar clusters. M83 is an XUV-disk prototype and the focus
of this proposal. It has an H-alpha surface brightness profile
characterized by a steep decline at the radius beyond which the
gaseous disk is thought to become dynamically stable {against collapse
and ensuing star formation}, but GALEX UV profiles show no "edge" at
this location. Our HST study of M83 aims to resolve this puzzling
discrepancy, confirmed in several XUV-disks, by searching for
Lyman-continuum producing O stars that are either absent or present
without nebulosity. HST provides the only means of resolving
individual massive stars in the FUV band at M83's distance. Without
HST, we lose the critical ability to photometrically classify O and B
stars. Our multiwavelength observations will also constrain the
history of star formation in the outer disk over Gyr timescales by
characterizing the evolved stellar population, both using resolved
giants and color analysis of the diffuse background.

FLIGHT OPERATIONS SUMMARY:

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

HSTARS:

10066 - GSacq(2,3,3) results in finelock backup (2,0,2) due to scan
step limit exceeded @363/1455Z The GSacq(2,3,3) scheduled at
363/14:54:37 -15:02:21 resulted to finelock backup (2,0,2) using
FGS-2, due to a Scan Step Limit Exceeded on FGS-3. Prior OBAD at
363/14:50:07 had total (RSS) attitude correction of 12.00 arcsecs.
Subsequent OBAD/MAP at 363/15:02:13 had total (RSS) attitude
correction of 7.16 arcsecs.

COMPLETED OPS REQUEST: (None)

COMPLETED OPS NOTES: (None)

SCHEDULED SUCCESSFUL
FGS GSacq 09 09
FGS REacq 05 05
OBAD with Maneuver 28 28

SIGNIFICANT EVENTS: (None)