Notice:
Due to the conversion of some ACS WFC or HRC observations into
WFPC2,
or NICMOS observations after the loss of ACS CCD science
capability
in January, there may be an occasional discrepancy between a
proposal's
listed (and correct) instrument usage and the abstract that
follows
it.
HUBBLE
SPACE TELESCOPE - Continuing to collect World Class Science
DAILY
REPORT # 4497
PERIOD
COVERED: UT November 29 , 2007 (DOY 333)
OBSERVATIONS
SCHEDULED
ACS/SBC
10907
New
Sightlines for the Study of Intergalactic Helium: A Dozen
High-Confidence,
UV-Bright Quasars from SDSS/GALEX
The
reionization of intergalactic helium is thought to have occurred
between
redshifts of about 3 and 4. Detailed study of HeII Lyman-alpha
absorption
toward a handful quasars at 2.7<z<3.3 demonstrates the great
potential
of such probes of the IGM, but the current critically-small
sample
limits confidence in resulting cosmological inferences. The
requisite
unobscured quasar sightlines to high-redshift are extremely
rare,
especially due to severe absorption in random intervening
Lyman-limit
systems, but SDSS provides thousands of z>3.1 quasars
potentially
suitable for HeII studies. We have cross-correlated SDSS
quasars
with GALEX UV sources to obtain a dozen new, very
high-confidence,
candidate quasars/sightlines {z=3.1 to 4.1} potentially
useful
for detailed HeII studies even with current HST instruments. We
propose
brief, 2-orbit per target, reconnaissance spectral exposures
with
the ACS SBC prism to definitively verify UV flux down to the HeII
break.
Our combined SDSS/GALEX selection insures a very high-yield of
confirmations,
as the quasars are already known to be UV-bright from
broadband
GALEX images. The additional sightlines, extending to very
high-redshift,
will directly enable ensemble spectral stacks, as well as
long
exposure follow-up spectra, at high S/N with the ACS/SBC
ultraviolet
prisms {or perhaps STIS or
measure
the spectrum and evolution of the ionizing background radiation,
the
evolution of HeII opacity, and the density of intergalactic baryons.
FGS
11211
An
Astrometric Calibration of Population II Distance Indicators
In
2002 HST produced a highly precise parallax for RR Lyrae. That
measurement
resulted in an absolute magnitude, M{V}= 0.61+/-0.11, a
useful
result, judged by the over ten refereed citations each year
since.
It is, however, unsatisfactory to have the direct,
parallax-based,
distance scale of Population II variables based on a
single
star. We propose, therefore, to obtain the parallaxes of four
additional
RR Lyrae stars and two Population II Cepheids, or
stars.
The Population II Cepheids lie with the RR Lyrae stars on a
common
K-band Period-Luminosity relation. Using these parallaxes to
inform
that relationship, we anticipate a zero-point error of 0.04
magnitude.
This result should greatly strengthen confidence in the
Population
II distance scale and increase our understanding of RR Lyrae
star
and Pop II Cepheid astrophysics.
WFPC2
10915
ACS
Nearby Galaxy Survey
Existing
HST observations of nearby galaxies comprise a sparse and
highly
non-uniform archive, making comprehensive comparative studies
among
galaxies essentially impossible. We propose to secure HST's
lasting
impact on the study of nearby galaxies by undertaking a
systematic,
complete, and carefully crafted imaging survey of ALL
galaxies
in the Local Universe outside the Local Group. The resulting
images
will allow unprecedented measurements of: {1} the star formation
history
{SFH} of a >100 Mpc^3 volume of the Universe with a time
resolution
of Delta[log{t}]=0.25; {2} correlations between spatially
resolved
SFHs and environment; {3} the structure and properties of thick
disks
and stellar halos; and {4} the color distributions, sizes, and
specific
frequencies of globular and disk clusters as a function of
galaxy
mass and environment. To reach these goals, we will use a
combination
of wide-field tiling and pointed deep imaging to obtain
uniform
data on all 72 galaxies within a volume-limited sample extending
to
~3.5 Mpc, with an extension to the M81 group. For each galaxy, the
wide-field
imaging will cover out to ~1.5 times the optical radius and
will
reach photometric depths of at least 2 magnitudes below the tip of
the
red giant branch throughout the limits of the survey volume. One
additional
deep pointing per galaxy will reach SNR~10 for red clump
stars,
sufficient to recover the ancient SFH from the color-magnitude
diagram.
This proposal will produce photometric information for ~100
million
stars {comparable to the number in the SDSS survey} and uniform
multi-
color images of half a square degree of sky. The resulting
archive
will establish the fundamental optical database for nearby
galaxies,
in preparation for the shift of high- resolution imaging to
the
near-infrared.
WFPC2
11103
A
Snapshot Survey of The Most Massive Clusters of Galaxies
We
propose the continuation of our highly successful SNAPshot survey of
a
sample of 125 very X-ray luminous clusters in the redshift range
0.3-0.7.
As demonstrated by the 25 snapshots obtained so far in Cycle14
and
Cycle15 these systems frequently exhibit strong gravitational
lensing
as well as spectacular examples of violent galaxy interactions.
The
proposed observations will provide important constraints on the
cluster
mass distributions, the physical nature of galaxy-galaxy and
galaxy-gas
interactions in cluster cores, and a set of optically bright,
lensed
galaxies for further 8-10m spectroscopy. All of our primary
science
goals require only the detection and characterization of
high-surface-brightness
features and are thus achievable even at the
reduced
sensitivity of WFPC2. Because of their high redshift and thus
compact
angular scale our target clusters are less adversely affected by
the
smaller field of view of WFPC2 than more nearby systems.
Acknowledging
the broad community interest in this sample we waive our
data
rights for these observations. Due to a clerical error at STScI our
approved
Cycle15 SNAP program was barred from execution for 3 months and
only
6 observations have been performed to date - reinstating this SNAP
at
Cycle16 priority is of paramount importance to reach meaningful
statistics.
WFPC2
11289
SL2S:
The Strong Lensing Legacy Survey
Recent
systematic surveys of strong galaxy-galaxy lenses {CLASS, SLACS,
GOODS,
etc.} are producing spectacular results for galaxy masses roughly
below
a transition mass M~10^13 Mo. The observed lens properties and
their
evolution up to z~0.2, consistent with numerical simulations, can
be
described by isothermal elliptical potentials. In contrast, modeling
of
giant arcs in X-ray luminous clusters {halo masses M >~10^13 Mo}
favors
NFW mass profiles, suggesting that dark matter halos are not
significantly
affected by baryon cooling. Until recently, lensing
surveys
were neither deep nor extended enough to probe the intermediate
mass
density regime, which is fundamental for understanding the assembly
of
structures. The CFHT Legacy Survey now covers 125 square degrees, and
thus
offers a large reservoir of strong lenses probing a large range of
mass
densities up to z~1. We have extracted a list of 150 strong lenses
using
the most recent CFHTLS data release via automated procedures.
Following
our first SNAPSHOT proposal in cycle 15, we propose to
continue
the Hubble follow-up targeting a larger list of 130 lensing
candidates.
These are intermediate mass range candidates {between
galaxies
and clusters} that are selected in the redshift range of 0.2-1
with
no a priori X-ray selection. The HST resolution is necessary for
confirming
the lensing candidates, accurate modeling of the lenses, and
probing
the total mass concentration in galaxy groups up to z~1 with the
largest
unbiased sample available to date.
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
06
06
FGS
REacq
05
05
OBAD
with Maneuver 22
22
SIGNIFICANT
EVENTS: (None)