Notice: For the foreseeable future, the daily reports may
contain
apparent discrepancies between some proposal descriptions
and the listed
instrument usage. This is due to the conversion of
previously approved
ACS WFC or HRC observations into WFPC2, or NICMOS
observations
subsequent to the loss of ACS CCD science capability in
late January.
HUBBLE SPACE TELESCOPE - Continuing to collect World Class
Science
DAILY REPORT # 4363
PERIOD COVERED: UT May 15, 2007 (DOY 135)
OBSERVATIONS SCHEDULED
WFPC2 10800
Kuiper Belt Binaries: Probes of Early Solar System
Evolution
Binaries in the Kuiper Belt are a scientific windfall: in
them we have
relatively fragile test particles which can be used as
tracers of the
early dynamical evolution of the outer Solar System. We
propose to
continue a Snapshot program using the ACS/HRC that has a
demonstrated
discovery potential an order of magnitude higher than the
HST
observations that have already discovered the majority of
known
transneptunian binaries. With this continuation we seek to
reach the
original goals of this project: to accumulate a
sufficiently large
sample in each of the distinct populations collected in
the Kuiper Belt
to be able to measure, with statistical significance, how
the fraction
of binaries varies as a function of their particular
dynamical paths
into the Kuiper Belt. Today's Kuiper Belt bears the
imprints of the
final stages of giant-planet building and migration;
binaries may offer
some of the best preserved evidence of that long-ago era.
WFPC2 10832
Solving the microlensing puzzle: An HST high-resolution
imaging approach
We propose to use the HST Advanced Camera for Surveys High
Resolution
Channel to obtain high resolution imaging data for 10
bona-fide LMC
microlensing events seen in the original MACHO survey. The
purpose of
this survey will be to assess whether or not the lens and
source stars
have separated enough to be resolved since the original
microlensing
event took place - about a decade has passed since the
original MACHO
survey and the HST WFPC2 follow-up observations of the
microlensing
events. If the components of the lensing event are
resolved, we will
determine the apparent magnitude and color of both the
lens and the
source stars. These data, in combination with Spitzer/IRAC
data and
Magellan near-IR JHK data, will be used to ascertain the
basic
properties of the lens stars. With the majority of the
microlensing
events in the original MACHO survey observed at the
highest spatial
resolution currently possible, we will be able to draw
important
conclusions as to what fraction of these events have
lenses which belong
to some population of dwarf stars in the disk and what
fraction must be
due to lenses in the halo or beyond. These data will
greatly increase
our understanding of the structure of the Galaxy by
characterizing the
stellar population responsible for the gravitational
microlensing.
ACS/SBC 10862
Comprehensive Auroral Imaging of Jupiter and Saturn during
the
International Heliophysical Year
A comprehensive set of observations of the auroral
emissions from
Jupiter and Saturn is proposed for the International
Heliophysical Year
in 2007, a unique period of especially concentrated
measurements of
space physics phenomena throughout the solar system. We
propose to
determine the physical relationship of the various auroral
processes at
Jupiter and Saturn with conditions in the solar wind at
each planet.
This can be accomplished with campaigns of observations,
with a sampling
interval not to exceed one day, covering at least one
solar rotation.
The solar wind plasma density approaching Jupiter will be
measured by
the New Horizons spacecraft, and a separate campaign near
opposition in
May 2007 will determine the effect of large-scale
variations in the
interplanetary magnetic field {IMF} on the Jovian aurora
by
extrapolation from near-Earth solar wind measurements. A
similar Saturn
campaign near opposition in Jan. 2007 will combine
extrapolated solar
wind data with measurements from a wide range of locations
within the
Saturn magnetosphere by Cassini. In the course of making
these
observations, it will be possible to fully map the auroral
footprints of
Io and the other satellites to determine both the local
magnetic field
geometry and the controlling factors in the
electromagnetic interaction
of each satellite with the corotating magnetic field and
plasma density.
Also in the course of making these observations, the
auroral emission
properties will be compared with the properties of the
near-IR
ionospheric emissions {from ground-based observations} and
non thermal
radio emissions, from ground-based observations for
Jupiter?s decametric
radiation and Cassini plasma wave measurements of the
Saturn Kilometric
Radiation {SKR}.
WFPC2 10798
Dark Halos and Substructure from Arcs & Einstein Rings
The surface brightness distribution of extended
gravitationally lensed
arcs and Einstein rings contains super-resolved
information about the
lensed object, and, more excitingly, about the smooth and
clumpy mass
distribution of the lens galaxies. The source and lens
information can
non-parametrically be separated, resulting in a direct
"gravitational
image" of the inner mass-distribution of
cosmologically-distant galaxies
{Koopmans 2005; Koopmans et al. 2006 [astro-ph/0601628]}.
With this goal
in mind, we propose deep HST ACS-F555W/F814W and
NICMOS-F160W WFC
imaging of 20 new gravitational-lens systems with
spatially resolved
lensed sources, of the 35 new lens systems discovered by
the Sloan Lens
ACS Survey {Bolton et al. 2005} so far, 15 of which are
being imaged in
Cycle-14. Each system has been selected from the SDSS and
confirmed in
two time- efficient HST-ACS snapshot programs {cycle
13&14}.
High-fidelity multi-color HST images are required {not
delivered by the
420s snapshots} to isolate these lensed images {properly
cleaned,
dithered and extinction-corrected} from the lens galaxy
surface
brightness distribution, and apply our "gravitational
maging" technique.
Our sample of 35 early-type lens galaxies to date is by
far the largest,
still growing, and most uniformly selected. This minimizes
selection
biases and small-number statistics, compared to smaller,
often
serendipitously discovered, samples. Moreover, using the WFC
provides
information on the field around the lens, higher S/N and a
better
understood PSF, compared with the HRC, and one retains
high spatial
resolution through drizzling. The sample of galaxy mass
distributions -
determined through this method from the arcs and Einstein
ring HST
images - will be studied to: {i} measure the smooth mass
distribution of
the lens galaxies {dark and luminous mass are separated
using the HST
images and the stellar M/L values derived from a joint
stellar-dynamical
analysis of each system}; {ii} quantify statistically and
individually
the incidence of mass-substructure {with or without
obvious luminous
counter- parts such as dwarf galaxies}. Since dark-matter
substructure
could be more prevalent at higher redshift, both results
provide a
direct test of this prediction of the CDM hierarchical
structure-formation model.
WFPC2 10888
Complexity in the Smallest Galaxies: Star Formation
History of the
Sculptor Dwarf Spheroidal
The Sculptor dwarf spheroidal galaxy {Scl dSph} is one of
the most
luminous of the Milky Way dSph satellites, suffers
virtually no
foreground confusion or reddening because of its high
galactic latitude,
and is nearby at 80 kpc from the Sun. It is of great
interest to
astronomy to understand the detailed histories of dSph
galaxies because
they may be survivors of the hierarchical merging process
that created
giant galaxies like our own. Despite this, the age
distribution of stars
in Scl dSph remains remarkably poorly constrained because
of a dearth of
high-quality color-magnitude diagrams {CMDs} of its
central regions. Scl
dSph is known to be complex on the basis of shallower
photometry, radial
velocity studies, and investigations of the metallicity;
however, the
age range of significant star-formation and the proportion
of stars
older and younger than 10 Gyr is still completely unknown.
The age of
the centrally concentrated, metal-rich population has
never been
measured. We propose to obtain deep optical images of the
core of Scl
dSph with WFPC2 in order to measure the temporal evolution
of its
star-formation rate over its entire lifetime. The ONLY way
to reliably
measure the variation in star-formation rate on Gyr
timescales at ages
of 10-13 Gyr is with photometry of a large number of stars
at and below
the oldest main-sequence turnoffs to magnitudes of {B,I} =
{25.1, 24.5}.
Because of the high stellar density and resulting image
crowding, it is
impossible to achieve the required level of photometric
precision except
with diffraction-limited imaging. These data will permit
the first
reliable measurement of the star-formation history of the
main body of
Scl dSph; limited inferences from WFPC2 data in an outer
field have been
made, but they were hindered not only by small number
statistics but by
the subsequent revelation of extremely strong population
gradients in
Scl dSph, such that the stars in the existing WFPC2 field
are not
representative of the galaxy as a whole. Our proposed
program will shed
strong new light on the formation processes of the
smallest galaxies.
Only by measuring the detailed early histories of galaxies
like Scl dSph
can we evaluate the impact of outside influences like
ram-pressure
stripping, tidal stirring, and photoionization feedback on
the evolution
of small galaxies.
WFPC2 10903
Resolving the LMC Microlensing Puzzle: Where are the
Lensing Objects?
We are requesting 12 HST orbits to continue to investigate
the nature of
the population that gives rise to the microlensing seen
towards the LMC.
This proposal builds on the cycle 14 HST program {10583}
and will
complement the study with 12 yet-to-be discovered
microlensing
candidates from Fall 2006. Our SuperMacho project is an
ongoing ground-
based survey on the CTIO 4m that has demonstrated the
ability to detect
LMC microlensing events via frame subtraction. The
combination of high
angular resolution and photometric accuracy with HST will
allow us to 1}
confrim that the detected flux excursions arise from LMC
stars, rather
than background supernovae or AGN, and 2} obtain reliable
baseline flux
measurements for the objects in their unlensed state. This
latter
measurement in important in determining the microlensing
optical depth
towards the LMC.
FLIGHT OPERATIONS SUMMARY:
Significant Spacecraft Anomalies: (The following are
preliminary reports
of potential non-nominal performance that will be
investigated.)
HSTARS:
10811 - REACQ(1,2,1) failed, Search Radius Limit Exceeded
on FGS 1
Upon acquisition of signal at 136/00:53:48, vehicle was in gyro control
with FGS 1 search radius limit flag set. REACQ(1,2,1) at 135/23:32:53
failed with search radius limit exceeded on FGS 1. OBAD map after GSACQ
failure showed RSS error of 45.81 arcseconds.
COMPLETED OPS REQUEST: (None)
COMPLETED OPS NOTES: (None)
SCHEDULED
SUCCESSFUL
FGS
GSacq
06
06
FGS
REacq
04
03
OBAD with Maneuver
20
20
SIGNIFICANT EVENTS: (None)