Daily 3838

HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT # 3838

PERIOD COVERED: DOY 103

OBSERVATIONS SCHEDULED

ACS/HRC/WFC 10389

ACS CCDs daily monitor - Cycle 13 - Part 2

This program consists of a set of basic tests to monitor, the read
noise, the development of hot pixels and test for any source of noise
in ACS CCD detectors. The files, biases and dark will be used to
create reference files for science calibration. This programme will be
for the entire lifetime of ACS.

ACS/WFC/NIC/NIC3/WFPC 10246 2 The HST survey of the Orion Nebula
Cluster

We propose a Treasury Program of 104 HST orbits to perform the
definitive study of the Orion Nebula Cluster, the Rosetta stone of
star formation. We will cover with unprecedented sensitivity {23-25
mag}, dynamic range {~12 mag}, spatial resolution {50mas}, and
simultaneous spectral coverage {5 bands} a ~450 square arcmin field
centered on the Trapezium stars. This represents a tremendous gain
over the shallow WFC1 study made in 1991 with the aberrated HST on an
area ~15 times smaller. We maximize the HST observing efficiency using
ACS/WFC and WFPC2 in parallel with two opposite roll angles, to cover
the same total field. We will assemble the richest, most accurate and
unbiased HR diagram for pre-main-sequence objects ever made. Combined
with the optical spectroscopy already available for ~1000 sources and
new deep near-IR imaging and spectroscopy {that we propose as Joint
HST-NOAO observations}, we will be able to attack and possibly solve
the most compelling questions on stellar evolution: the calibration of
pre-main-sequence evolutionary tracks, mass segration and the
variation of the initial mass function in different environments, the
evolution of mass accretion rates vs. age and environment, disk
dissipation in environments dominated by hard vs. soft-UV radiation,
stellar multiplicity vs. disk fraction. In addition, we expect to
discover and classify an unknown, but substantial, population of
pre-Main Sequence binaries, low mass stars and brown dwarfs down to
~10 MJup. This is also the best possible way to discover dark
silhouette disks in the outskirts of the Orion Nebula and study their
evolutionary status through multicolor imaging. This program is timely
and extremely well leveraged to other programs targeting Orion: the
ACS H-alpha survey of the Orion Nebula, the recently completed 850ks
ultradeep Chandra survey, the large GTO programs to be performed with
SIRTF, plus the availability of 2MASS and various deep JHK surveys of
the core recently done with 8m class telescopes.

ACS/WFC/NIC3 10339

PANS

Type Ia supernovae {SNe Ia} provide the only direct evidence for an
accelerating universe, an extraordinary result that needs the most
rigorous test. The case for cosmic acceleration rests on the
observation that SNe Ia at z = 0.5 are about 0.25 mag fainter than
they would be in a universe without acceleration. A powerful and
straightforward way to assess the reliability of the SN Ia measurement
and the conceptual framework of its interpretation is to look for
cosmic deceleration at z 1. This would be a clear signature of a
mixed dark-matter and dark-energy universe. Systematic errors in the
SNe Ia result attributed to grey dust or cosmic evolution of the SN Ia
peak luminosity would not show this change of sign. We have obtained a
toehold on this putative ``epoch of deceleration'' with SN 1997ff at z
= 1.7, and 3 more at z 1 from our Cycle 11 program, all found and
followed by HST. However, this is too important a test to rest on just
a few objects, anyone of which could be subject to a lensed
line-of-sight or misidentification. Here we propose to extend our
measurement with observations of twelve SNe Ia in the range 1.0 z
1.5 or 6 such SNe Ia and 1 ultradistant SN Ia at z = 2, that will be
discovered as a byproduct from proposed Treasury and DD programs.
These objects will provide a much firmer foundation for a conclusion
that touches on important questions of fundamental physics.

ACS/WFC/WFPC2 10136

Post-AGB Stars in the Halo of M81

Post-asymptotic-giant-branch {PAGB} stars of spectral types A-F are
the brightest members of Population II. We have shown, using
ground-based observations, that PAGB stars have tremendous potential
as highly efficient standard candles and as tracers of halo
populations and late stellar evolution. Our analysis of PAGB stars in
archival HST images of M32, based on the equivalent of one orbit of
HST time, precisely reproduces the accepted distance. We propose to
obtain ACS/WFC and WFPC2 images of fields in the halo of M81, as
another test of the PAGB method. We show that 4 orbits of HST data
will produce a distance of comparable accuracy to the much more
laborious Cepheid technique. If successful on M81, we will propose in
the next cycle to measure the distance to Virgo using our method, a
distance ladder that has only two rungs {trigonometric parallaxes of
subdwarfs to calibrate PAGB stars in globular clusters, and then PAGB
stars in Virgo}.

NIC1/NIC2/NIC3 8792

NICMOS Post-SAA calibration - CR Persistence Part 3

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 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 images. Each observation will need its
own CRMAP, as different SAA passages leave different imprints on the
NICMOS detectors.

WFPC2 10112

HST Observations of Astrophysically Important Visual Binaries

This is a continuation of a project begun in Cycle 7 and continued up
through Cycle 11. The program consists of annual or biannual WFPC2 or
FGS observations of three visual binary stars that will ultimately
yield fundamental astrophysical results, once their orbits and masses
are determined. Our targets are the following: {1} Procyon {P = 41
yr}, for which our first WFPC2 images yielded an extremely accurate
angular separation of the bright F star and its much fainter
white-dwarf companion. Combined with ground-based astrometry of the
bright star, our observation significantly revised downward the
derived masses, and brought Procyon A into excellent agreement with
theoretical evolutionary tracks for the first time. With the continued
monitoring proposed here, we will obtain masses to an accuracy of
better than 1%, providing a testbed for theories of both Sun- like
stars and white dwarfs. {2} G 107-70, a close double white dwarf {P =
19 yr} that promises to add two accurate masses to the tiny handful of
white-dwarf masses that are directly known from dynamical
measurements. {3} Mu Cas {P = 21 yr}, a famous metal- deficient G
dwarf for which accurate masses will lead to the stars' helium
contents, with cosmological implications.

FLIGHT OPERATIONS SUMMARY:

Significant Spacecraft Anomalies: (The following are preliminary
reports of potential non-nominal performance that will be
investigated.) None

COMPLETED OPS REQs: None

OPS NOTES EXECUTED: None

SCHEDULED SUCCESSFUL FAILURE TIMES
FGS Gsacq 10 10
FGS Reacq 6 6
FHST Update 11 11
LOSS of LOCK



SIGNIFICANT EVENTS: None