Status Report

NASA Hubble Space Telescope Daily Report #4837

By SpaceRef Editor
April 21, 2009
Filed under , ,

HUBBLE SPACE TELESCOPE – Continuing to collect World Class Science


PERIOD COVERED: 5am April 20 – 5am April 21, 2009 (DOY


ACS/SBC 11982

Spanning the Reionization History of IGM Helium: a Large and Efficient
HST Spectral Survey of Far-UV-Bright Quasars
The reionization of IGM helium is thought to have occurred at
redshifts of z=3 to 4. Detailed studies of HeII Lyman-alpha absorption
toward a handful of QSOs at 2.7 of such IGM probes, but the small sample size and redshift range limit
confidence in cosmological inferences. The requisite unobscured
sightlines to high-z are extremely rare, but we’ve cross-correlated
10, 000 z>2.8 SDSS DR7 (and other) quasars with GALEX GR4 UV sources
to obtain 550 new, high confidence, sightlines potentially useful for
HST HeII studies; and in cycle 15-16 trials we demonstrated the
efficacy of our SDSS/GALEX selection approach identifying 9 new HeII
quasars at unprecedented 67% efficiency. We propose the first
far-UV-bright HeII quasar survey that is both large in scale and also
efficient, via 2-orbit reconnaissance ACS/SBC prism spectra toward a
highly select subset of 40 new SDSS/GALEX quasars at 3.1 will provide a community resource list that includes 5 far-UV-bright
(restframe) HeII sightlines in each of 8 redshift bins spanning
3.14), enabling superb
post-SM4 follow-up spectra with COS or STIS. But simultaneously and
independent of any SM4 uncertainties, we will hereby directly obtain
10-orbit UV spectral stacks from the 5 HeII quasars in each of the 8
redshift bins to trace the reionization history of IGM helium over at
least 3.1 variance and individual object pathology. Our new high-yield HeII
sightline sample and spectral stacks, covering a large redshift range,
will allow confident conclusions about the spectrum and evolution of
the ionizing background, the evolution of HeII opacity, the density of
IGM baryons, and the epoch of helium reionization.

WFPC2 11302

WFPC2 CYCLE 16 Standard Darks – Part III

This dark calibration program obtains dark frames every week in order
to provide data for the ongoing calibration of the CCD dark current
rate, and to monitor and characterize the evolution of hot pixels.
Over an extended period these data will also provide a monitor of
radiation damage to the CCDs.

WFPC2 11793

WFPC2 Cycle 16 Internal Monitor

This calibration proposal is the Cycle 15 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.

WFPC2 11975

UV Light from Old Stellar Populations: a Census of UV Sources in
Galactic Globular Clusters

In spite of the fact that HST has been the only operative
high-resolution eye in the UV-window over the last 18 years, no
homogeneous UV survey of Galactic globular clusters (GGCs) has been
performed to date. In order to fill this gap in the stellar population
studies, we propose a program that exploits the unique capability of
the WFPC2 and the SBC in the far-/mid- UV for securing deep UV imaging
of 46 GGCs. The proposed observations will allow to study with
unprecedented accuracy the hottest GGC stars, comprising the extreme
horizontal branch (HB) stars and their progeny (the so-called
AGB-manque’, and Post-early AGB stars), and “exotic stellar
populations” like the blue straggler stars and the interacting
binaries. The targets have been selected to properly sample the GGC
metallicity/structural parameter space, thus to unveil any possible
correlation between the properties of the hot stellar populations and
the cluster characteristics. In addition, most of the targets have
extended HB “blue tails”, that can be properly studied only by means
of deep UV observations, especially in the far-UV filters like the
F160BW, that is not foreseen on the WFC3. This data base is
complemented with GALEX observations in the cluster outermost regions,
thus allowing to investigate any possible trend of the UV-bright
stellar types over the entire radial extension of the clusters.
Although the hottest GGC stars are just a small class of “special”
objects, their study has a broad relevance in the context of structure
formation and chemical evolution in the early Universe, bringing
precious information on the basic star formation processes and the
origin of blue light from galaxies. Indeed, the proposed observations
will provide the community with an unprecedented data set suitable for
addressing a number of still open astrophysical questions, ranging
from the main drivers of the HB morphology and the mass loss
processes, to the origin of the UV upturn in elliptical galaxies, the
dating of distant systems from integrated light, and the complex
interplay between stellar evolution and dynamics in dense stellar
aggregates. In the spirit of constructing a community resource, we
entirely waive the proprietary period for these observations.

WFPC2 11981

FUV Imaging Survey of Galactic Open Clusters

We propose a WFPC2 FUV imaging survey of 6 Galactic open clusters with
ages ranging from 1 Myr to 300 Myr complemented with NUV/optical
imaging of the same fields. No such survey has ever been attempted
before in the FUV at the resolution of WFPC2 (indeed, no WFPC2 FUV
images of any Galactic open cluster exist in the HST archive) and,
since WFPC2 will be retired in SM4 and none of the other HST
instruments can do FUV imaging of bright objects, this is the last
chance to do such a survey before another UV telescope is launched.
This survey will provide a new perspective on young/intermediate age
Galactic clusters and a key template for the study of star formation
at high redshift, where the intensity peak we observe in the
optical/NIR from Earth is located in the FUV in its rest frame. For
clusters still associated with an H II region, UV imaging maps the
continuum emission of the ionized gas and the radiation scattered by
background dust and, combined with optical nebular images, can be used
to determine the 3-D structure of the H II region. For all young
clusters, FUV+NUV+optical photometry can be used to study the UV
excesses of T-Tauri stars. For clusters older than ~40 Myr, the same
photometric combination is the easiest method to detect companion
white dwarfs which are invisible using only the optical and NIR. WFPC2
is also an excellent instrument to discover close companions around
bright stars and improve our knowledge of their multiplicity fraction.
Finally, for all clusters, the combination of high-spatial-resolution
UV and optical photometry can be used to simultaneously measure the
temperature, extinction, extinction law, distance, and existence of
companions (resolved and unresolved) and, thus, produce clean HR
diagrams with resolved cluster membership and much-reduced systematic


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


11775 – REAcq(2,1,1) scheduled at 110/09:28:24 failed due to receiving

Observations affected: WFPC 42 – 44, Proposal ID# 11981




FGS GSAcq 04 04
FGS REAcq 09 08
OBAD with Maneuver 26 26


SpaceRef staff editor.