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.
