Daily Report #4814

HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT****** #4814

PERIOD COVERED: 5am March 18 - 5am March 19, 2009 (DOY
*************************** 077/0900z-078/0900z)

OBSERVATIONS SCHEDULED

ACS/SBC 11151

Evaluating the Role of Photoevaporation of Protoplanetary Disk
Dispersal

Emission produced by accretion onto the central star leads to
photoevaporation, which may play a fundamental role in disk dispersal.
Models of disk photoevaporation by the central star are challenged by
two potential problems: the emission produced by accretion will be
substantially weaker for low-mass stars, and photoevaporation must
continue as accretion slows. Existing FUV spectra of CTTSs are biased
to solar-mass stars with high accretion rates, and are therefore
insufficient to address these problems. We propose use HST/ACS SBC
PR130L to obtain FUV spectra of WTTSs and of CTTSs at low masses and
mass accretion rates to provide crucial data to evaluate
photoevaporation models. We will estimate the FUV and EUV luminosities
of low-mass CTTSs with small mass accretion rates, CTTSs with
transition disks and slowed accretion, and of magnetically-active
WTTSs.

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 11789

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 W Vir
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 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 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 i 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).

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************** 08***************** 08
FGS REAcq************** 05***************** 05
OBAD with Maneuver **** 24***************** 24

SIGNIFICANT EVENTS: (None)