Daily Report # 4423

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 W Vir
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)