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 # 4333

PERIOD COVERED: UT April 04, 2007 (DOY 093)

OBSERVATIONS SCHEDULED

NIC1 10859

Precise Measurements of Sgr A* Flare Activity

Correlated X-ray and near-IR flare emission from Sgr A*, the closest
supermassive black hole, contains information about the hydrodynamics,
energetics, and accretion behavior of matter within the innermost ten
Schwarzschild radii of the hole. We propose HST/NICMOS observations of
near-IR flares, in conjunction with already approved obsrevations using
XMM-Newton {214 ksec} and CSO {3 nights}, which can make the precise, new
measurements necessary to understand the radiation mechanism and low
luminosity of Sgr A*. HST/NICMOS is required due to its very low and stable
background, and its stable, tightly focused PSF, which allow accurate
measurement of fainter flares than can be observed using groundbased
adaptive optics systems. We will measure the spectral index distribution,
the time-averaged flux and duration of flares, and the statistics of flare
activity, and will confirm previously reported quasi-periodic variability.
These measurements will have far-reaching implications for testing the
inverse Compton scattering {ICS} and synchrotron models of low-luminosity
flares, for understanding the process of accretion onto and outflow from
supermassive black holes, and for constraining the acceleration mechanism of
flares and the inferred black hole spin. This knowledge, in turn, will help
us understand more generally low-luminosity AGN and X-ray binaries in a very
low/quiescent accretion state.

NIC1/NIC2/NIC3 8795

NICMOS Post-SAA calibration - CR Persistence Part 6

A new proceedure proposed to alleviate the CR-persistence problem of NICMOS.
Dark frames will be obtained immediately upon exiting the SAA contour 23,
and everytime 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 DARKSs. 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 i mages. Each observation will need its own CRMAP, as
different SAA passages leave different imprints on the NICMOS detectors.

WFPC2 11022

WFPC2 Cycle 15 Decontaminations and Associated Observations

This proposal is for the WFPC2 decons. Also included are instrument monitors
tied to decons: photometric stability check, focus monitor, pre- and
post-decon internals {bias, intflats, kspots, & darks}, UV throughput check,
VISFLAT sweep, and internal UV flat check.

WFPC2 11083

The Structure, Formation and Evolution of Galactic Cores and Nuclei

A surprising result has emerged from the ACS Virgo Cluster Survey {ACSVCS},
a program to obtain ACS/WFC gz imaging for a large, unbiased sample of 100
early-type galaxies in the Virgo Cluster. On subarcsecond scales {i.e.,
0.1"-1"}, the HST brightness profiles vary systematically from the
brightest giants {which have nearly constant surface brightness cores} to
the faintest dwarfs {which have compact stellar nuclei}. Remarkably, the
fraction of galaxy mass contributed by the nuclei in the faint galaxies is
identical to that contributed by supermassive black holes in the bright
galaxies {0.2%}. These findings strongly suggest that a single mechanism is
responsible for both types of Central Massive Object: most likely internally
or externally modulated gas inflows that feed central black holes or lead to
the formation of "nuclear star clusters". Understanding the history of gas
accretion, star formation and chemical enrichment on subarcsecond scales has
thus emerged as the single most pressing question in the study of nearby
galactic nuclei, either active or quiescent. We propose an ambitious HST
program {199 orbits} that constitutes the next, obvious step forward:
high-resolution, ultraviolet {WFPC2/F255W} and infrared {NIC1/F160W} imaging
for the complete ACSVCS sample. By capitalizing on HST's unique ability to
provide high-resolution images with a sharp and stable PSF at UV and IR
wavelengths, we will leverage the existing optical HST data to obtain the
most complete picture currently possible for the history of star formation
and chemical enrichment on these small scales. Equally important, this
program will lead to a significant improvement in the measured structural
parameters and density distributions for the stellar nuclei and the
underlying galaxies, and provide a sensitive measure of "frosting" by young
stars in the galaxy cores. By virtue of its superb image quality and stable
PSF, NICMOS is the sole instrument capable of the IR observations proposed
here. In the case of the WFPC2 observations, high-resolution UV imaging {
0.1"} is a capability unique to HST, yet one that could be lost at any any
time.

FLIGHT OPERATIONS SUMMARY:

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

HSTARS: (None)

COMPLETED OPS REQUEST: (None)

COMPLETED OPS NOTES: (None)

SCHEDULED SUCCESSFUL

FGS GSacq 10 10
FGS REacq 04 04
OBAD with Maneuver 26 26

SIGNIFICANT EVENTS:

Flash Report: Update on WFPC2 performance at lowered temperature.

We continue to received additional test data from WFPC2 at the new reduced
operating temperature. All results so far look excellent.

Observations of the Omega Cen star cluster were taken on Sunday to evaluate
the image quality. No significant change was seen. The stellar FWHM on the
PC1 CCD was 1.75 ± 0.03 pixels prior to the temperature change, and 1.76 ±
0.02 pixels afterwards. Similar results are seen in all 4 CCDs.

Bias levels in the WF4 CCD continue to be relatively stable (283 to 303 DN
range) , and are close to the normal value ~311 DN.

Small changes in the relative positions of the CCDs in the HST focal plane
continue to be confirmed, typically around ~0.1 pixel. These are very
similar to the changes seen across the January and February 2006 temperature
adjustments, and should be of no consequence.

This is the third temperature reduction we have performed, and we have yet
to see any negative effects from them. This suggests we should be able to
keep the WF4 CCD operational until SM4 via additional temperature
reductions.