HUBBLE SPACE TELESCOPE - Continuing to collect World Class
Science
DAILY REPORT #4849
PERIOD COVERED: 5am May 6 - 5am May 7, 2009 (DOY
126/0900z-127/0900z)
OBSERVATIONS SCHEDULED
WFPC2 11972
Investigating the Early Solar System with Distant Comet
Nuclei
We propose 85 orbits of imaging observations with the
WFPC2 to get
nucleus size estimates for 8 well observed dynamically new
and
long-period comets at large distances from the sun when
their activity
levels are low. This will increase the sample of these
nucleus sizes by
nearly 50%, but will more than double the selection of
comets for which
we can run thermal models. Small icy bodies are the best
preserved
remnants of planet formation, and we have recently found
that
observationally constrained thermal models can distinguish
differences
in microphysical properties of comet nuclei. The new HST
data will
enable the first exploration of physical conditions in
different regions
of the early solar nebula.
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 11987
The Recent Star Formation History of SINGS Galaxies
The Spitzer Legacy project SINGS provided a unique view of
the current
state of star formation and dust in a sample of galaxies
of all Hubble
types. This multi-wavelength view allowed the team to
create current
star formation diagnostics that are independent of the
dust content and
increased our understanding of the dust in galaxies. Even
so, using the
SINGS data alone we can only make rough estimates of the
recent star
formation history of these galaxies. The lack of U-band
observations
means that it is impossible to estimate the ages of young
clusters. In
addition, the low resolution of the Spitzer and
ground-based
observations means that what appear to be individual
Spitzer sources can
actually be composed of many individual clusters with
varying ages. In
this proposal we plan to address this missing area in
SINGS by obtaining
high-resolution WFPC2 UBVI observations to accurately find
and determine
the ages of the young stellar clusters in a subset of the
SINGS
galaxies. These observations will greatly enhance the
legacy value of
the SINGS observations while also directly answering
questions
pertaining to star formation in galaxies.
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
04
04
FGS
REAcq
10
10
OBAD with Maneuver
28
28
SIGNIFICANT EVENTS: (None)