Daily #4072

HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT #4072

PERIOD COVERED: UT March 16, 2006 (DOY 075)

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 10599

Multi-color imaging of two 1 Gyr old debris disks within 20 pc of the
Sun: Astrophysical mirrors of our Kuiper

We report the first scattered light detections of two debris disk
around an F star and a K star using optical coronagraphy and the
Hubble Space Telescope. With ages ~1 Gyr, these are the oldest debris
disks thus far seen in the optical. We propose deep, multi-roll angle
coronagraphic imaging with HST ACS and NICMOS to confirm and
characterize the disks in terms of structure and composition. The
disks appear to have belt-like morphology that is consistent with the
existence of planetary companions or other perturbing bodies. Since
these disks are close to our Kuiper Belt in an evolutionary context,
detailed understanding of their mass, structure and composition will
provide a fresh perspective for inferring the history and properties
of our own trans-Neptunian region.

ACS/SBC 10736

ACS UV contamination monitor

The observations consist of imaging and spectroscopy with SBC and HRC
of the cluster NGC 6681 in order to monitor the temporal evolution of
the UV sensitivity of the SBC and the HRC. All UV modes except for SBC
PR130L will be used.

ACS/WFC 10496

Decelerating and Dustfree: Efficient Dark Energy Studies with
Supernovae and Clusters

We propose a novel HST approach to obtain a dramatically more useful
"dust free" Type Ia supernovae {SNe Ia} dataset than available with
the previous GOODS searches. Moreover, this approach provides a
strikingly more efficient search-and-follow-up that is primarily pre-
scheduled. The resulting dark energy measurements do not share the
major systematic uncertainty at these redshifts, that of the
extinction correction with a prior. By targeting massive galaxy
clusters at z 1 we obtain a five-times higher efficiency in
detection of Type Ia supernovae in ellipticals, providing a
well-understood host galaxy environment. These same deep cluster
images then also yield fundamental calibrations required for future
weak lensing and Sunyaev-Zel'dovich measurements of dark energy, as
well as an entire program of cluster studies. The data will make
possible a factor of two improvement on supernova constraints on dark
energy time variation, and much larger improvement in systematic
uncertainty. They will provide both a cluster dataset and a SN Ia
dataset that will be a longstanding scientific resource.

ACS/WFC 10524

Blue Stragglers: a key stellar population to probe internal cluster
dynamics

This proposal is part of a coordinated project devoted to understand
the interplay of globular cluster {GC} dynamics and the formation and
evolution of blue straggler stars {BSS}. By using a combination of HST
and ground-based observations we are constructing complete BSS surveys
in a sample of GCs; complete BSS surveys require mid-UV HST
observations in the center and wide field CCD ground based
observations under excellent seeing conditions of the exterior. Up to
now only four clusters have been surveyed in this way and the results
are surprising: in three GCs {M3, 47 Tuc, NGC 6752} we have discovered
that the BSS radial distribution is bimodal, highly peaked in the
cluster center, rapidly decreasing at intermediate radii and rising
again at large radii {Ferraro et al. 1997, 2004, Sabbi et al. 2004},
conversely BSS population in Omega Centauri does not show any
signature of the segregation which would be expected for a class of
objects arising from either stellar interactions or binarity {Ferraro
et al. 2005}. These observational facts are opening a new prospective
in the study of the formation processes and evolution of BSS in GCs.
By using extensive simulations, we demonstrated that the spatial
distribution of BSS observed in 47 Tuc can be only reproduced if a
sizable fraction of BSS is generated {via mass transfer in primordial
binaries} in the peripheral region of the cluster {Mapelli et al
2004}, thus excluding a purely collisional formation scenario. Here we
propose mid-UV imaging of a few clusters suspected of harboring a
large population of central BSS and a few known to have many BSS the
external region. These are good candidates for determining accurate
BSS radial distributions. The modest amount of time proposed here will
go far to determine the ubiquity of BSS bimodality and to constrain
models of dynamical evolution. Since we believe the proposed
observations would be useful to the entire stellar community {for
multifold purposes} we waive the propretary period.

NIC1/NIC2/NIC3 8793

NICMOS Post-SAA calibration - CR Persistence Part 4

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. The keyword 'USEAFTER=date/time' will also be added to
the header of each POST-SAA DARK frame. The keyword must be populated
with the time, in addition to the date, because HST crosses the SAA ~8
times per day so each POST-SAA DARK will need to have the appropriate
time specified, for users to identify the ones they need. Both the raw
and processed images will be archived as POST-SAA DARKSs. Generally we
expect that all NICMOS science/calibration observations started within
50 minutes of leaving an SAA will need such maps to remove the CR
persistence from the science images. Each observation will need its
own CRMAP, as different SAA passages leave different imprints on the
NICMOS detectors.

NICS3 10754

Spectrophotometric Standards for Cross-Observatory Calibration

This program will obtain NICMOS spectrophotometry of four main
sequence A stars and four K giants, each selected from the Spitzer
IRAC photometric calibration target and/or candidate calibration
target lists. These observations will supplement existing HST
observations of DA white dwarfs and solar analogs, and will provide a
broad base of stellar types for spectrophotometric cross calibration
of HST, Spitzer, and eventually JWST. The targets are chosen to be
faint enough for unsaturated observations with JWST NIRSPEC, yet still
bright enough for high signal to noise in relatively short
observations with HST+NICMOS and with Spitzer+IRAC.

FLIGHT OPERATIONS SUMMARY:

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

HSTARS:

10172 - GSAcq(2,1,2) failed to RGA control (T2G) due to stop flag on
FGS-1 @ 075/2205z

The GSAcq(2,1,2) scheduled at 075/22:05:53 - 22:13:58 failed to RGA
control due to stop flag (QF1STOPF) on FGS-1. Pre-acquisition OBADs
were successful. OBAD2 at 075/22:01:23 had total (RSS) attitude
correction value of 15.12 arcseconds.

COMPLETED OPS REQUEST: (None)

COMPLETED OPS NOTES:

SCHEDULED SUCCESSFUL FAILURE TIMES
FGS
GSacq 14 13 075/2205z
(HSTAR 10172)
FGS REacq 01 01
OBAD with Maneuver 30 30

SIGNIFICANT EVENTS: (None)