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)