Daily Report #4811

HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT****** #4811

PERIOD COVERED: 5am March 13 - 5am March 16, 2009 (DOY
*************************** 072/0900z-075/0900z)

OBSERVATIONS SCHEDULED

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.

WFPC2 11986

Completing HST's Local Volume Legacy

Nearby galaxies offer one of the few laboratories within which stellar
populations can be tied to multi-wavelength observations. They are
thus essential for calibrating and interpreting key astrophysical
observables, such as broad-band luminosities, durations and energy
input from starbursts, and timescales of UV, H-alpha, and FIR
emission. The study of stellar populations in nearby galaxies requires
high-resolution observations with HST, but HST's legacy for this
limited set of galaxies remains incomplete.

As a first attempt to establish this legacy, The ACS Nearby Galaxy
Survey Treasury (ANGST) began observations in late 2006. ANGST was
designed to carry out a uniform multi-color survey of a volume-limited
sample of ~70 nearby galaxies that could be used for systematic
studies of resolved stellar populations. The resulting data provide
nuanced constraints on the processes which govern star formation and
galaxy evolution, for a well-defined population of galaxies. All
photometry for the survey has been publicly released.

However, the failure of ACS 4.5 months after ANGST began taking data
led to a drastic reduction in the planned survey. The loss is
two-fold. First, the goals of completeness and uniformity were greatly
compromised, impacting global comparison studies. Second, the variety
of observed star formation histories was reduced. Given that we have
never found two galaxies with identical star formation histories, and
fully sampling the population allows us to catch those few systems
whose star formation rates and metallicities place the strongest
constraints on key astrophysical processes.

Here we propose WFPC2 observations of all remaining galaxies within
the Local Volume (D3.5Mpc) for which current HST observations are
insufficient for meaningful stellar population studies. We will use
these observations for research on the star formation histories of
individual galaxies and the Local Volume, detailed calibrations of
star formation rate indicators, and the durations of starbursts. We
will also make them publicly available through the ANGST archive to
support future research. The proposed observations will finally
complete a lasting legacy of HST

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.

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 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 11944

Binaries at the Extremes of the H-R Diagram

We propose to use HST/Fine Guidance Sensor 1r to survey for binaries
among some of the most massive, least massive, and oldest stars in our
part of the Galaxy. FGS allows us to spatially resolve binary systems
that are too faint to observe using ground-based, speckle or optical
long baseline interferometry, and too close to resolve with AO. We
propose a SNAP-style program of single orbit FGS TRANS mode
observations of very massive stars in the cluster NGC 3603, luminous
blue variables, nearby low mass main sequence stars, cool subdwarf
stars, and white dwarfs. These observations will help us to (1)
identify systems suitable for follow up studies for mass
determination, (2) study the role of binaries in stellar birth and in
advanced evolutionary states, (3) explore the fundamental properties
of stars near the main sequence-brown dwarf boundary, (4) understand
the role of binaries for X-ray bright systems, (5) find binaries among
ancient and nearby subdwarf stars, and (6) help calibrate the white
dwarf mass - radius relation.

FGS 11704

The Ages of Globular Clusters and the Population II Distance Scale

Globular clusters are the oldest objects in the universe whose age can
be accurately determined. The dominant error in globular cluster age
determinations is the uncertain Population II distance scale. We
propose to use FGS 1r to obtain parallaxes with an accuracy of 0.2
milliarcsecond for 9 main sequence stars with [Fe/H] -1.5. This will
determine the absolute magnitude of these stars with accuracies of
0.04 to 0.06mag. This data will be used to determine the distance to
24 metal-poor globular clusters using main sequence fitting. These
distances (with errors of 0.05 mag) will be used to determine the ages
of globular clusters using the luminosity of the subgiant branch as an
age indicator. This will yield absolute ages with an accuracy 5%,
about a factor of two improvement over current estimates. Coupled with
existing parallaxes for more metal-rich stars, we will be able to
accurately determine the age for globular clusters over a wide range
of metallicities in order to study the early formation history of the
Milky Way and provide an independent estimate of the age of the
universe.

The Hipparcos database contains only 1 star with [Fe/H] -1.4 and an
absolute magnitude error less than 0.18 mag which is suitable for use
in main sequence fitting. Previous attempts at main sequence fitting
to metal-poor globular clusters have had to rely on theoretical
calibrations of the color of the main sequence. Our HST parallax
program will remove this source of possible systematic error and yield
distances to metal-poor globular clusters which are significantly more
accurate than possible with the current parallax data. The HST
parallax data will have errors which are 10 times smaller than the
current parallax data. Using the HST parallaxes, we will obtain main
sequence fitting distances to 11 globular clusters which contain over
500 RR Lyrae stars. This will allow us to calibrate the absolute
magnitude of RR Lyrae stars, a commonly used Population II distance
indicator.

FLIGHT OPERATIONS SUMMARY:

Significant Spacecraft Anomalies: (The following are preliminary
reports of potential non-nominal performance that will be
investigated.)

HSTARS:

11721 - GSAcq (2,1,1) had failed to Fine Lock Back-up (2,0,2). The
Guide Star acquisition was scheduled from 14:53:19 - 15:00:43.

Observations possibly affected: WFPC 195 - 196, Proposal ID# 11986.

REAcq (2,1,1) scheduled from 16:27:05 - 16:34:29, resulted in Fine
Lock Back-up (2,0,2).

Observations possibly affected: WFPC 197, Proposal ID# 11986.

11723 - GSAcq (2,1,1) scheduled from 073/19:40:56 - 19:48:20, and
REAcq (2,1,1) scheduled at 21:14:44 - 21:22:08, both resulted in Fine
Lock Back-up (2,0,2).

Observations possibly affected: WFPC 199 - 201, Proposal ID# 11986.

11724 - REACQ (2,1,1) at 073/22:49:56 ended in Fine Lock Backup on FGS
2 with QF1STOPF and QSTOP flags set at 22:54:13.

Observations possibly affected: WFPC 202, proposal ID# 11986.

11725 - GSAcq and REAcq (1,2,2) failed due to Search Radius Limit
Exceeded on FGS-1. GSAcq scheduled 074/20:11:08 - 20:18:26z and REAcq
scheduled 074/21:27:33 - 21:34:51z.

Observations affected: WFPC 217 - 232, Proposal ID# 11983.

COMPLETED OPS REQUEST: (None)

COMPLETED OPS NOTES: (None)

*********************** SCHEDULED***** SUCCESSFUL

FGS GSAcq************** 19***************** 18
FGS REAcq************** 20***************** 19
OBAD with Maneuver **** 78***************** 78

SIGNIFICANT EVENTS: (None)