Notice:
Due to the conversion of some ACS WFC or HRC observations into
WFPC2,
or NICMOS observations after the loss of ACS CCD science
capability
in January, there may be an occasional discrepancy between a
proposal's
listed (and correct) instrument usage and the abstract that
follows
it.
HUBBLE
SPACE TELESCOPE - Continuing to collect World Class Science
DAILY
REPORT # 4423
PERIOD
COVERED: UT August 09, 2007 (DOY 221)
OBSERVATIONS
SCHEDULED
WFPC2
10583
Resolving
the LMC Microlensing Puzzle: Where Are the Lensing Objects ?
We
are requesting 32 HST orbits to help ascertain the nature of the
population
that gives rise to the observed set of microlensing events
towards
the LMC. The SuperMACHO project is an ongoing ground-based
survey
on the CTIO 4m that has demonstrated the ability to detect LMC
microlensing
events in real-time via frame subtraction. The improvement
in
angular resolution and photometric accuracy available from HST will
allow
us to 1} confirm that the detected flux excursions arise from LMC
source
stars rather than extended objects {such as for background
supernovae
or AGN}, and 2} obtain reliable baseline flux measurements
for
the objects in their unlensed state. The latter measurement is
important
to resolve degeneracies between the event timescale and
baseline
flux, which will yield a tighter constraint on the microlensing
optical
depth.
FGS
11211
An
Astrometric Calibration of Population II Distance Indicators
In 2002
HST produced a highly precise parallax for RR Lyrae. That
measurement
resulted in an absolute magnitude, M{V}= 0.61+/-0.11, a
useful
result, judged by the over ten refereed citations each year
since.
It is, however, unsatisfactory to have the direct,
parallax-based,
distance scale of Population II variables based on a
single
star. We propose, therefore, to obtain the parallaxes of four
additional
RR Lyrae stars and two Population II Cepheids, or
stars.
The Population II Cepheids lie with the RR Lyrae stars on a
common
K-band Period-Luminosity relation. Using these parallaxes to
inform
that relationship, we anticipate a zero-point error of 0.04
magnitude.
This result should greatly strengthen confidence in the
Population
II distance scale and increase our understanding of RR Lyrae
star
and Pop II Cepheid astrophysics.
NIC1
10889
The
Nature of the Halos and Thick Disks of Spiral Galaxies
We
propose to resolve the extra-planar stellar populations of the thick
disks
and halos of seven nearby, massive, edge-on galaxies using ACS,
NICMOS,
and WFPC2 in parallel. These observations will provide accurate
star
counts and color-magnitude diagrams 1.5 magnitudes below the tip of
the
Red Giant Branch sampled along the two principal axes and one
intermediate
axis of each galaxy. We will measure the metallicity
distribution
functions and stellar density profiles from star counts
down
to very low average surface brightnesses, equivalent to ~32 V-mag
per
square arcsec. These observations will provide the definitive HST
study
of extra-planar stellar populations of spiral galaxies. Our
targets
cover a range in galaxy mass, luminosity, and morphology and as
function
of these galaxy properties we will provide: - The first
systematic
study of the radial and isophotal shapes of the diffuse
stellar
halos of spiral galaxies - The most detailed comparative study
to
date of thick disk morphologies and stellar populations - A
comprehensive
analysis of halo and thick disk metallicity distributions
as
a function of galaxy type and position within the galaxy. - A
sensitive
search for tidal streams - The first opportunity to directly
relate
globular cluster systems to their field stellar population We
will
use these fossil records of the galaxy assembly process preserved
in
the old stellar populations to test halo and thick disk formation
models
within the hierarchical galaxy formation scheme. We will test
LambdaCDM
predictions on sub-galactic scales, where it is difficult to
test
using CMB and galaxy redshift surveys, and where it faces its most
serious
difficulties.
NIC1/NIC2/NIC3
8794
NICMOS Post-SAA calibration - CR Persistence Part 5
A
new procedure proposed to alleviate the CR-persistence problem of
NICMOS.
Dark frames will be obtained immediately upon exiting the SAA
contour
23, and every time a NICMOS exposure is scheduled within 50
minutes
of coming out of the SAA. The darks will be obtained in parallel
in
all three NICMOS Cameras. The POST-SAA darks will be non- standard
reference
files available to users with a USEAFTER date/time mark. The
keyword
'USEAFTER=date/time' will also be added to the header of each
POST-SAA
DARK frame. The keyword must be populated with the time, in
addition
to the date, because HST crosses the SAA ~8 times per day so
each
POST-SAA DARK will need to have the appropriate time specified, for
users
to identify the ones they need. Both the raw and processed images
will
be archived as POST-SAA DARKs. Generally we expect that all NICMOS
science/calibration
observations started within 50 minutes of leaving an
SAA
will need such maps to remove the CR persistence from the science
images.
Each observation will need its own CRMAP, as different SAA
passages
leave different imprints on the NICMOS detectors.
NIC2
10852
Coronagraphic
Polarimetry with NICMOS: Dust grain evolution in T Tauri
stars
The
formation of planetary systems is intimately linked to the dust
population
in circumstellar disks, thus understanding dust grain
evolution
is essential to advancing our understanding of how planets
form.
By combining {1} the coronagraphic polarimetry capabilities of
NICMOS,
{2} powerful 3-D radiative transfer codes, and {3} observations
of
objects known to span the Class II-III stellar evolutionary phases,
we
will gain crucial insight into dust grain growth. By observing
objects
representative of a known evolutionary sequence of YSOs, we will
be
able to investigate how the dust population evolves in size and
distribution
during the crucial transition from a star+disk system to a
system
containing planetesimals. When combine with our previous study on
dust
grain evolution in the Class I-II phase, the proposed study will
help
to establish the fundamental time scales for the depletion of
ISM-like
grains: the first step in understanding the transformation from
small
submicron sized dust grains, to large millimeter sized grains, and
untimely
to planetary bodies.
WFPC2
11030
WFPC2
WF4 Temperature Reduction #3
In
the fall of 2005, a serious anomaly was found in images from the WF4
CCD
in WFPC2. The WF4 CCD bias level appeared to have become unstable,
resulting
in sporadic images with either low or zero bias level. The
severity
and frequency of the problem was rapidly increasing, making it
possible
that WF4 would soon become unusable if no work-around were
found.
Examination of bias levels during periods with frequent WFPC2
images
showed low and zero bias episodes every 4 to 6 hours. This
periodicity
is driven by cycling of the WFPC2 Replacement Heater, with
the
bias anomalies occurring at the temperature peaks. The other three
CCDs
{PC1, WF2, and WF3} appear to be unaffected and continue to operate
properly.
Lowering the Replacement Heater temperature set points by a
few
degrees C effectively eliminates the WF4 anomaly. On 9 January 2006,
the
upper set point of the WFPC2 Replacement Heater was reduced from
14.9C
to 12.2C. On 20 February 2006, the upper set point was reduced
from
12.2C to 11.3C, and the lower set point was reduced from 10.9C to
10.0C.
These changes restored the WF4 CCD bias level; however, the bias
level
has begun to trend downwards again, mimicking its behavior in late
2004
and early 2005. A third temperature reduction is planned for March
2007.
We will reduce the upper set point of the heater from 11.3C to
10.4C
and the lower set point from 10.0C to 9.1C. The observations
described
in this proposal will test the performance of WFPC2 before and
after
this temperature reduction. Additional temperature reductions may
be needed
in the future, depending on the performance of WF4. Orbits:
internal
26, external 1
WFPC2
11202
The
Structure of Early-type Galaxies: 0.1-100 Effective Radii
The
structure, formation and evolution of early-type galaxies is still
largely
an open problem in cosmology: how does the Universe evolve from
large
linear scales dominated by dark matter to the highly non-linear
scales
of galaxies, where baryons and dark matter both play important,
interacting,
roles? To understand the complex physical processes
involved
in their formation scenario, and why they have the tight
scaling
relations that we observe today {e.g. the Fundamental Plane}, it
is
critically important not only to understand their stellar structure,
but
also their dark-matter distribution from the smallest to the largest
scales.
Over the last three years the SLACS collaboration has developed
a
toolbox to tackle these issues in a unique and encompassing way by
combining
new non-parametric strong lensing techniques, stellar
dynamics,
and most recently weak gravitational lensing, with
high-quality
Hubble Space Telescope imaging and VLT/Keck spectroscopic
data
of early-type lens systems. This allows us to break degeneracies
that
are inherent to each of these techniques separately and probe the
mass
structure of early-type galaxies from 0.1 to 100 effective radii.
The
large dynamic range to which lensing is sensitive allows us both to
probe
the clumpy substructure of these galaxies, as well as their
low-density
outer haloes. These methods have convincingly been
demonstrated,
by our team, using smaller pilot- samples of SLACS lens
systems
with HST data. In this proposal, we request observing time with
WFPC2
and NICMOS to observe 53 strong lens systems from SLACS, to obtain
complete
multi-color imaging for each system. This would bring the total
number
of SLACS lens systems to 87 with completed HST imaging and
effectively
doubles the known number of galaxy-scale strong lenses. The
deep
HST images enable us to fully exploit our new techniques, beat down
low-number
statistics, and probe the structure and evolution of
early-type
galaxies, not only with a uniform data-set an order of
magnitude
larger than what is available now, but also with a fully
coherent
and self-consistent methodological approach!
WFPC2
11307
Completing
the ACS Nearby Galaxy Survey with WFPC2
We
are requesting 25 orbits of Director's Discretionary Time to complete
the
primary science goals of our highly-ranked ACS Nearby Galaxy Survey
Treasury
program {ANGST}. Our program lost ~2/3 of its orbits due to the
ACS
failure. Roughly half of these were restored as a result of an
appeal
to the Telescope Time Review Board which re-scoped the program.
The
Board's response to our appeal was explicit in terms of which
targets
were to be observed and how. We were directed to request
Director's
discretionary time for the components of the appeal which
were
not granted by the Review Board, but which were vital to the
success
of the program. The observing strategy for ANGST is two-fold: to
obtain
one deep field per galaxy which enables derivation of an accurate
ancient
star formation history, and to obtain radial tilings sufficient
for
recovering the full star formation history. The Review Board granted
WFPC2
observations for deep fields in 7 galaxies, but no time for radial
tilings.
However, recovering the full star formation history of a galaxy
is
not possible without additional radial coverage. We have searched the
archives
for observations which may be used in place of the tilings
{conceding
some of the Treasury goals, but providing significant
constraints
on the full star formation history}, and have identified
suitable
observations for all but two of the galaxies. Here we request
DD
time for radial tilings for those last two galaxies.
FLIGHT
OPERATIONS SUMMARY:
Significant
Spacecraft Anomalies: (The following are preliminary reports
of
potential non-nominal performance that will be investigated.)
HSTARS:
10936
- GSacq(1,3,3) failed to RGA control
GSacq(1,3,3) scheduled at 222/06:35:29 failed during LOS due to
Scan
step limit exceeded on FGS 1. OBAD1 showed errors of V1= 105.80,
V2=133.96, V3=317.36, and RSS=360.36. OBAD2 showed errors of
V1=-1.26,
V2=-1.19, V3=0.37, RSS=1.77.
COMPLETED
OPS REQUEST: (None)
COMPLETED
OPS NOTES: (None)
SCHEDULED
SUCCESSFUL
FGS
GSacq
09
08
FGS
REacq
05
05
OBAD
with Maneuver
28
28
SIGNIFICANT
EVENTS: (None)