Status Report

NASA Hubble Space Telescope Daily Report #4847

By SpaceRef Editor

May 5, 2009

Filed under Hubble Space Telescope, Space Telescope Science Institute, US

HUBBLE SPACE TELESCOPE – Continuing to collect World Class Science

DAILY REPORT #4847

PERIOD COVERED: 5am May 4 – 5am May 5, 2009 (DOY 124/0900z-125/0900z)

OBSERVATIONS SCHEDULED

ACS/SBC 11980
Deep FUV Imaging of Cooling Flow Clusters

We propose to take deep ACS FUV images of a carefully selected sample
of 19 bright central galaxies in nearby galaxy clusters. This program
is the last critical element of a comprehensive investigation of the
impact of stellar and AGN feedback on the local galaxy cluster
environment. The HST images will complement new, high-resolution,
Halpha images obtained with the recently commissioned
Maryland-Magellan Tunable Filter (MMTF) on the Baade 6.5m telescope,
archival Chandra, VLA, and GALEX data, and on-going H2/NIR
observations. The MMTF data have revealed unsuspected filamentary
complexes in several systems. The GALEX data often show hints of
extended NUV and FUV emission on a similar scale, but their poor
spatial resolution prevents meaningful comparison with the MMTF data.
The HST data will provide this much needed gain in resolution. The
combined radio-H2-Halpha-FUV-X-ray dataset will allow us to derive
with unprecedented precision the role of the AGN, hot stars, shocks,
and relativistic particles on the excitation and thermodynamics of the
multi-phase intracluster and interstellar media in these systems. This
is an important question since the formation and evolution of most
cluster galaxies have likely been affected by these processes.

FGS 11704

The Ages of Globular Clusters and the Population II Distance Scale
Globular clusters are the oldest objects in the universe whose age can
be accurately determined. The dominant error in globular cluster age
determinations is the uncertain Population II distance scale. We
propose to use FGS 1r to obtain parallaxes with an accuracy of 0.2
milliarcsecond for 9 main sequence stars with [Fe/H] < -1.5. This will
determine the absolute magnitude of these stars with accuracies of
0.04 to 0.06mag. This data will be used to determine the distance to
24 metal-poor globular clusters using main sequence fitting. These
distances (with errors of 0.05 mag) will be used to determine the ages
of globular clusters using the luminosity of the subgiant branch as an
age indicator. This will yield absolute ages with an accuracy 5%,
about a factor of two improvement over current estimates. Coupled with
existing parallaxes for more metal-rich stars, we will be able to
accurately determine the age for globular clusters over a wide range
of metallicities in order to study the early formation history of the
Milky Way and provide an independent estimate of the age of the
universe.

The Hipparcos database contains only 1 star with [Fe/H] < -1.4 and an
absolute magnitude error less than 0.18 mag which is suitable for use
in main sequence fitting. Previous attempts at main sequence fitting
to metal-poor globular clusters have had to rely on theoretical
calibrations of the color of the main sequence. Our HST parallax
program will remove this source of possible systematic error and yield
distances to metal-poor globular clusters which are significantly more
accurate than possible with the current parallax data. The HST
parallax data will have errors which are 10 times smaller than the
current parallax data. Using the HST parallaxes, we will obtain main
sequence fitting distances to 11 globular clusters which contain over
500 RR Lyrae stars. This will allow us to calibrate the absolute
magnitude of RR Lyrae stars, a commonly used Population II distance
indicator.

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 11804

WFPC2 Closeout Calibration — CTE Effects on Standard Star
Observations of the primary standard star GRW+70D5824 are made at
several different places on the CCD to directly estimate the impact of
CTE. All four CCDs are evaluated. Filters F170W and F555W are used to
evaluate the effects of background and different PSF shapes / sizes.

WFPC2 11956
Hubble Heritage: Side B

We propose a program of 39 orbits to observe 6 targets with WFPC2
following a successful return to science using side B electronics.
These observations will be used for Hubble Heritage releases in the
months leading up to servicing mission 4. Because of launch delays,
our reserve of releasable images is growing dangerously slim. We are
proposing here to replenish one of our important lines of
communication with the public.

We have carefully chosen targets that can efficiently use single
pointings of WFPC2 to obtain images of visually striking and
astrophysically interesting targets. Observations will reach high S/N
and will be dithered and subsampled to improve the resolution and
pixel scale to near ACS/WFC3 quality at a modest cost in exposure
time. Most of the observations will schedule in the interim between a
return to science and the availability of new science proposals that
may be selected in response to an interim call for proposals.

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
uncertainties.

WFPC2 11988
Searching for Intermediate Mass Black Holes in Globular Clusters via
Proper Motions

The unambiguous detection of an intermediate mas black hole (IMBH) in
a globular star cluster would be a major achievement for the Hubble
Space Telescope. It is critical to know whether or not IMBHs exist in
the centers of clusters in order to understand the dynamical evolution
of dense stellar systems. Also, n IMBH detection would prove the
existence of BHs in an entirely new mass range. Observationally, the
search has been hampered by the low number of stars with known
velocities in the central few arcseconds. This limits measurements of
the stellar velocity dispersion in the region where the gravitational
influence of any IMBH would be felt. Existing IMBH claims in the
literature have all been called into question, and have all been based
on line-of-sight velocities from spectroscopy. In cycle 13, we
obtained ACS/HRC observations for 5 nearby Galactic globular clusters
for a new proper motion study. Here, we request WFPC2/PC observations
of these clusters, all of which are observable in Feb-May 2009. This 4
year baseline will allow us to measure the proper motions of stars
into the very center of each cluster, and either detect or place firm
constraints on the presence of an IMBH. In addition, we will determine
whether or not the clusters rotate or show any anisotropy in their
motions. Our small (<75 orbit) program meets the criteria of
addressing high impact science (IMBH detection) using innovative
methods (proper motions).