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 (D<3.5Mpc) 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)