HUBBLE SPACE TELESCOPE - Continuing to collect World Class
Science
DAILY REPORT #4839
PERIOD COVERED: 5am April 22 - 5am April 23, 2009 (DOY
112/0900z-113/0900z)
OBSERVATIONS SCHEDULED
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 11979
WFPC2 Imaging of Fomalhaut b: Determining its Orbit and
Testing for
H-alpha Emission
Fomalhaut is a bright nearby star that harbors a belt of
dusty material
with a morphology that has been used to predict the
presence of a
shepherding planet. With ACS/HRC coronagraphy, we have
achieved the
direct detection of a planet candidate (Fomalhaut b) in
F606W and F814W.
The planet candidate lies 18 AU interior to the dust belt
and we detect
counterclockwise orbital motion in two epochs of
observations (2004 and
2006). Fomalhaut b has mass no greater than three Jupiter
masses based
on an analysis of its luminosity, including non-detections
at infrared
wavelengths, and the dynamical argument that a
significantly more
massive object would disrupt the dust belt. Variability at
optical
wavelengths and the brightness in the F606W passband
suggest additional
sources of luminosity such as starlight reflected from a
circumplanetary
ring system. A second possibility that has been invoked
for substellar
objects is a significant contribution of H-alpha emission.
Here we
propose follow-up WFPC2 observations to test the
possibility that the
F606W flux is contaminated by H-alpha emission. We demonstrate
that the
detection of Fomalhaut b using WFPC2 is feasible using
roll
deconvolution. Furthermore, a detection of Fomalhaut b in
2009 will
provide a crucial third epoch for astrometry.
With the existing two epochs of data, the orbit of
Fomalhaut b cannot be
determined uniquely. The third epoch will be used to test
the prediction
of apsidal alignment and more accurately determine the
dynamical mass of
Fomalhaut b. If apsidal mis-alignment is found between the
planet and
the belt, this result would point to the existence of
still other
planets lurking unseen in the Fomalhaut system.
WFPC2 11983
An Imaging Survey of Protoplanetary Disks and Brown Dwarfs
in the
Chamaeleon I Region
We propose to carry out a HST/WFPC2 survey of young brown
dwarfs, Class
I and Class II sources in the Chamaelon I region, one of
the
best-studied star-forming regions, in order to investigate
the link
between disk evolution and the formation of
substellar-mass objects. We
will use deep broad-band imaging in the I and z-equivalent
HST bands to
unveil the unknown population of substellar binary
companions, down to a
few Jupiter masses for separations of a few tens of AU. We
will also
perform narrow-band imaging to directly detect accreting
circumstellar
disks and jets around brown dwarfs, Class-I and class-II
objects.
Chamaelon I is nearly coeaval of Orion (~1-2Myr) but at
~1/3 its
distance, allowing 3x higher resolution and 10x more flux
for comparable
objects. Unlike Orion, low-mass objects and protoplanetary
disks in
Chamaeleon I have been extensively studied with Spitzer,
but not yet
with the HST. The Chamaeleon I region is an ideal HST
target, as it lies
in the CVZ of the HST and therefore it is easily
accessible any time of
the year with long orbits.
FLIGHT OPERATIONS SUMMARY:
Significant Spacecraft Anomalies: (The following are
preliminary reports
of potential non-nominal performance that will be
investigated.)
HSTARS:
11779 - GSAcq(2,0,2) at 112/20:54:49 failed to RGA
control with Search Radius Limit
exceeded on FGS 2.
Observations affected: WFPC 169 - 174, Proposal ID# 11979.
COMPLETED OPS REQUEST: (None)
COMPLETED OPS NOTES: (None)
SCHEDULED
SUCCESSFUL
FGS
GSAcq 09
08
FGS
REAcq
05
05
OBAD with Maneuver
28
27
SIGNIFICANT EVENTS: (None)