Daily Report #4801

HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT****** #4801

PERIOD COVERED: 5am February 27 - 5am March 2, 2009 (DOY
***************************** 058/1000z-061/1000z)

OBSERVATIONS SCHEDULED

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

ACS/SBC 11984

Observing Saturn's High Latitude Polar Auroras

Planetary auroral emissions are critical indicators of how the
magnetospheres of the planets work. Recently, a new component of
Saturn's auroral emissions, i.e. high latitude auroras inside the main
auroral oval, have been observed by the Cassini spacecraft during
otherwise quiet auroral conditions. Such high latitude auroras are of
immense interest since they occur on magnetic flux tubes connected to
a region that is key to the overall dynamics of the system, the
magnetotail, and where if conventional theories regarding Saturn's
magnetosphere are correct there should not be any auroras. These faint
auroral emissions have not been previously observed by the Hubble
Space Telescope (HST). However, the unique oblique viewing geometry
afforded during early 2009 due to Saturn's orbital longitude will
result in the apparent brightening of these polar emissions due to the
limb-brightening effect, with the result that they may be observable
by HST for the first ever time. In addition, at this time the Cassini
spacecraft will be in a high latitude orbit, with a trajectory that
will take it through these magnetic flux tubes, providing essential
simultaneous in situ data. This is the last time Cassini will be in
such an orbit during its mission as currently scheduled and HST is the
only instrument capable of obtaining sustained long-term observations
of Saturn's auroras. These observations will address the following:

Does Saturn exhibit high latitude UV auroras observable by HST? Where
do these auroras occur, and at what altitude? How do these auroras
behave over time? How variable are they? Are they periodic? How do
they behave with respect to other auroral components? What processes
drive these auroras?

Are these auroras generated by processes internal to the magnetosphere
or are they driven by the solar wind? How do the infrared (IR) auroras
relate to the ultraviolet (UV) auroras?

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 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.

WFPC2 11797

Supplemental WFPC2 CYCLE 16 Intflat Linearity Check and Filter
Rotation Anomaly Monitor

Supplemental observations to 11029, to cover period from Aug 08 to
SM4. Intflat observations will be taken to provide a linearity check:
the linearity test consists of a series of intflats in F555W, in each
gain and each shutter. A combination of intflats, visflats, and
earthflats will be used to check the repeatability of filter wheel
motions. (Intflat sequences tied to decons, visits 1-18 in prop 10363,
have been moved to the cycle 15 decon proposal 11022 for easier
scheduling.)

Note: long-exposure WFPC2 intflats must be scheduled during ACS
anneals to prevent stray light from the WFPC2 lamps from contaminating
long ACS external exposures.

Note: These are supplemental observations to cover June to SM4 (Oct 8
'08) + 6 months.

WFPC2 11795

WFPC2 Cycle 16 UV Earth Flats

Monitor flat field stability. This proposal obtains sequences of earth
streak flats to improve the quality of pipeline flat fields for the
WFPC2 UV filter set. These Earth flats will complement the UV earth
flat data obtained during cycles 8-15.

WFPC2 11794

Cycle 16 Visible Earth Flats

This proposal monitors flatfield stability. This proposal obtains
sequences of Earth streak flats to construct high quality flat fields
for the WFPC2 filter set. These flat fields will allow mapping of the
OTA illumination pattern and will be used in conjunction with previous
internal and external flats to generate new pipeline superflats. These
Earth flats will complement the Earth flat data obtained during cycles
4-15.

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.

ACS/SBC 11681

A Search for Ultraviolet Emission Filaments in Cool Core Clusters

We propose to use ACS SBC imaging to seek ultraviolet CIV emission
filaments in clusters of galaxies exhibiting strong cool-core X-ray
emission and optical line emission filaments. These short observations
are crafted to test thermal conduction models for the filament
excitation, and can significantly impact our understanding of the
overall physical processes dominant in the galaxy cluster ISM.

FGS 11298

Calibrating Cosmological Chronometers: White Dwarf Masses

We propose to use HST/FGS1R to determine White Dwarf {WD} masses. The
unmatched resolving power of HST/FGS1R will be utilized to follow up
four selected WD binary pairs. This high precision obtained with
HST/FGS1R simply cannot be equaled by any ground based technique. This
proposed effort complements that done by CoI Nelan in which a sample
of WDs is being observed with HST/FGS1R. This proposal will
dramatically increase the number of WDs for which dynamical mass
measurements are possible, enabling a better calibration of the WD
mass-radius relation, cooling curves, initial to final mass relations,
and ultimately giving important clues to the star formation history of
our Galaxy and the age of its disk as well as in other galaxies. {This
project is part of Subasavage's PhD thesis work at Georgia State
University.}

FLIGHT OPERATIONS SUMMARY:

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

HSTARS:

11702 - GSAcq (2,1,2) results in fine lock backup (2,0,2) using FGS-2
@060/07:50:13z

Observations possibly affected: WFPC #58-73, Proposal ID#11983.

COMPLETED OPS REQUEST: (None)

COMPLETED OPS NOTES: (None)

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

FGS GSAcq***************** 23************* 23
FGS REAcq***************** 12************* 12
OBAD with Maneuver*** * ** 70************* 70

SIGNIFICANT EVENTS: (None)