Daily Report #4795

HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT***** #4795

PERIOD COVERED: 5am February 19 - 5am February 20, 2009 (DOY
*************************** 050/1000z-051/1000z)

OBSERVATIONS SCHEDULED

WFPC2 11590

Observing the IR Catastrophe in a Deflagration Type Ia Supernova

Our lack of understanding of Type Ia supernova (SN Ia) explosions
limits our confidence in their use for cosmology. While there is broad
agreement that these objects represent the explosions of white dwarfs,
the details of the explosion mechanism are not well-understood.
Recently, we have identified an internally homogeneous subclass of SNe
Ia whose photometric and spectroscopic peculiarities make them quite
distinct from normal SNe Ia. Models suggest we may be seeing the
result of an explosion with a subsonic burning front, called a
deflagration. We propose to test SN Ia models by obtaining late-time
photometry for SN 2008A, a recent, nearby example of this subclass,
using ACS and WFC3 on HST. We will accurately measure the late-time
photometric decline rate and spectral energy distribution (SED). These
observations will allow us to test whether the ejecta contain the
large amount of oxygen predicted by certain models. We also aim to
detect major evolution of the SED expected due to the "IR catastrophe,
" a change in the dominant cooling mechanism in the ejecta, as
generically predicted by models but only hinted at by current
observations.

FGS 11944/11943

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.

WFPC2 11974

High-resolution Imaging for 9 Very Bright, Spectroscopically
Confirmed, Group-scale Lenses

There are large samples of strong lenses that probe small (galaxy)
scale masses (e.g., SLACS, SQLS, COSMOS). There are also large samples
of strong lenses that probe large (rich cluster) scale masses (e.g.,
various rich Abell clusters, the Hennawi et al. 2008 SDSS sample). The
sample of strong lenses that probe intermediate (group/cluster-core)
scale masses, however, is sparse, and so any significant additions to
this sample are important. Here we present a sample of strong lenses
that not only probe these intermediate scales but are also quite
bright, since the sample is based almost entirely upon data from the
SDSS, a relatively shallow and poor-resolution survey, at least in
comparison to most other strong lens hunting grounds, such as COSMOS
and CFHTLS. What we lack are the high-resolution imaging data needed
to construct detailed lensing models, to probe the mass and light
profiles of the lensing galaxies and their environments, and to
characterize the morphologies of the lensed (source) galaxies. Only
HST can provide these data, and so we are proposing here for 81 orbits
of deep WFPC2 F450W, F606W and F814W imaging, for 9 of our best and
brightest intermediate-scale lensing systems with known spectroscopic
redshifts and with Einstein radii between 4 and 8 arcsec.

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

FLIGHT OPERATIONS SUMMARY:

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

HSTARS:

#11688 REAcq (2,1,2) Loss of Lock while guiding under two FGS during
LOS @050/17:25z

Observations possibly affected: WFPC #117-118, Proposal ID #11986.

COMPLETED OPS REQUEST:** None

COMPLETED OPS NOTES:****** None

*************************** SCHEDULED***** SUCCESSFUL***********
FAILURE TIME

FGS GSAcq****************** 06******************* 06
FGS REAcq****************** 07******************* 07
OBAD with Maneuver***** *** 26******************* 26
LOSS of LOCK********************************************** *****
050/17:25z

SIGNIFICANT EVENTS: (None)