Daily Report # 4441

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***** # 4441

PERIOD COVERED: UT September 05, 2007 (DOY 248)

OBSERVATIONS SCHEDULED

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.

FGS 11212

Filling the Period Gap for Massive Binaries

The current census of binaries among the massive O-type stars is
seriously incomplete for systems in the period range from years to
millennia because the radial velocity variations are too small and the
angular separations too close for easy detection. Here we propose to
discover binaries in this observational gap through a Faint Guidance
Sensor SNAP survey of relatively bright targets listed in the Galactic
O Star Catalog. Our primary goal is to determine the binary frequency
among those in the cluster/association, field, and runaway groups. The
results will help us assess the role of binaries in massive star
formation and in the processes that lead to the ejection of massive
stars from their natal clusters. The program will also lead to the
identification of new, close binaries that will be targets of long
term spectroscopic and high angular resolution observations to
determine their masses and distances. The results will also be
important for the interpretation of the spectra of suspected and newly
identified binary and multiple systems.

WFPC2 10915

ACS Nearby Galaxy Survey

Existing HST observations of nearby galaxies comprise a sparse and
highly non-uniform archive, making comprehensive comparative studies
among galaxies essentially impossible. We propose to secure HST's
lasting impact on the study of nearby galaxies by undertaking a
systematic, complete, and carefully crafted imaging survey of ALL
galaxies in the Local Universe outside the Local Group. The resulting
images will allow unprecedented measurements of: {1} the star
formation history {SFH} of a 100 Mpc^3 volume of the Universe with a
time resolution of Delta[log{t}]=0.25; {2} correlations between
spatially resolved SFHs and environment; {3} the structure and
properties of thick disks and stellar halos; and {4} the color
distributions, sizes, and specific frequencies of globular and disk
clusters as a function of galaxy mass and environment. To reach these
goals, we will use a combination of wide-field tiling and pointed deep
imaging to obtain uniform data on all 72 galaxies within a
volume-limited sample extending to ~3.5 Mpc, with an extension to the
M81 group. For each galaxy, the wide-field imaging will cover out to
~1.5 times the optical radius and will reach photometric depths of at
least 2 magnitudes below the tip of the red giant branch throughout
the limits of the survey volume. One additional deep pointing per
galaxy will reach SNR~10 for red clump stars, sufficient to recover
the ancient SFH from the color-magnitude diagram. This proposal will
produce photometric information for ~100 million stars {comparable to
the number in the SDSS survey} and uniform multi- color images of half
a square degree of sky. The resulting archive will establish the
fundamental optical database for nearby galaxies, in preparation for
the shift of high- resolution imaging to the near-infrared.

WFPC2 11029

WFPC2 CYCLE 15 Intflat Linearity Check and Filter Rotation Anomaly
Monitor

Intflat observations will be taken to provide a linearity check: the
linearity test consists of a series of intflats in F555W, in each gain
and each shutter. A combination of intflats, visflats, and earthflats
will be used to check the repeatability of filter wheel motions.
{Intflat sequences tied to decons, visits 1-18 in prop 10363, have
been moved to the cycle 15 decon proposal xxxx for easier scheduling.}
Note: long-exposure WFPC2 intflats must be scheduled during ACS
anneals to prevent stray light from the WFPC2 lamps from contaminating
long ACS external exposures.

WFPC2 11038

Narrow Band and Ramp Filter Closeout

These observations are to improve calibration of narrow band and ramp
filters. We also test for changes in the filter properties during
WFPC2's 14 years on-board HST.

WFPC2 11178

Probing Solar System History with Orbits, Masses, and Colors of
Transneptunian Binaries

The recent discovery of numerous transneptunian binaries {TNBs} opens
a window into dynamical conditions in the protoplanetary disk where
they formed as well as the history of subsequent events which sculpted
the outer Solar System and emplaced them onto their present day
heliocentric orbits. To date, at least 47 TNBs have been discovered,
but only about a dozen have had their mutual orbits and separate
colors determined, frustrating their use to investigate numerous
important scientific questions. The current shortage of data
especially cripples scientific investigations requiring statistical
comparisons among the ensemble characteristics. We propose to obtain
sufficient astrometry and photometry of 23 TNBs to compute their
mutual orbits and system masses and to determine separate primary and
secondary colors, roughly tripling the sample for which this
information is known, as well as extending it to include systems of
two near-equal size bodies. To make the most efficient possible use of
HST, we will use a Monte Carlo technique to optimally schedule our
observations.

WFPC2 11201

Systemic and Internal motions of the Magellanic Clouds: Third Epoch
Images

In Cycles 11 and 13 we obtained two epochs of ACS/HRC data for fields
in the Magellanic Clouds centered on background quasars. We used these
data to determine the proper motions of the LMC and SMC to better than
5% and 15% respectively. These are by far the best determinations of
the proper motions of these two galaxies. The results have a number of
unexpected implications for the Milky Way-LMC-SMC system. The implied
three-dimensional velocities are larger than previously believed, and
are not much less than the escape velocity in a standard 10^12 solar
mass Milky Way dark halo. Orbit calculations suggest the Clouds may
not be bound to the Milky Way or may just be on their first passage,
both of which would be unexpected in view of traditional
interpretations of the Magellanic Stream. Alternatively, the Milky Way
dark halo may be a factor of two more massive than previously
believed, which would be surprising in view of other observational
constraints. Also, the relative velocity between the LMC and SMC is
larger than expected, leaving open the possibility that the Clouds may
not be bound to each other. To further verify and refine our results
we now request an epoch of WFPC2/PC data for the fields centered on 40
quasars that have at least one epoch of ACS imaging. We request
execution in snapshot mode, as in our previous programs, to ensure the
most efficient use of HST resources. A third epoch of data of these
fields will provide crucial information to verify that there are no
residual systematic effects in our previous measurements. More
importantly, it will increase the time baseline from 2 to 5 yrs and
will increase the number of fields with at least two epochs of data.
This will reduce our uncertainties correspondingly, so that we can
better address whether the Clouds are indeed bound to each other and
to the Milky Way. It will also allow us to constrain the internal
motions of various populations within the Clouds, and will allow us to
determine a distance to the LMC using rotational parallax.

WFPC2 11292

The Ring Plane Crossings of Uranus in 2007

The rings of Uranus turn edge-on to Earth in May and August 2007. In
between, we will have a rare opportunity to see the unlit face of the
rings. With the nine optically thick rings essentially invisible, we
will observe features and phenomena that are normally lost in their
glare. We will use this opportunity to search thoroughly for the
embedded "shepherd" moons long believed to confine the edges of the
rings, setting a mass limit roughly 10 times smaller than that of the
smallest shepherd currently known, Cordelia. We will measure the
vertical thicknesses of the rings and study the faint dust belts only
known to exist from a single Voyager image. We will also study the
colors of the newly-discovered faint, outer rings; recent evidence
suggests that one ring is red and the other blue, implying that each
ring is dominated by a different set of physical processes. We will
employ near- edge-on photometry from 2006 and 2007 to derive the
particle filling factor within the rings, to observe how ring epsilon
responds to the "traffic jam" as particles pass through its narrowest
point, and to test the latest models for preserving eccentricities and
apse alignment within the rings. Moreover, this data set will allow us
to continue monitoring the motions of the inner moons, which have been
found to show possibly chaotic orbital variations; by nearly doubling
the time span of the existing Hubble astrometry, the details of the
variations will become much clearer.

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************** 09**************** 09
FGS REacq************** 05**************** 05
OBAD with Maneuver **** 28**************** 28

SIGNIFICANT EVENTS:

NICMOS Recovery Flash Report:

NICMOS recovery procedure was successfully completed at 246/15:03 UTC.
This procedure enabled NICMOS Buffer Box 2 and transitioned NICMOS up
to Operate mode and then back down to SAAOPER. The mode transition was
performed in order to refresh the Buffer Box (BB) telemetry. The
current temperatures for BB1, 2 and 3 are -1.94, -7.76 and -2.42
respectively.

NICMOS is now configured to intercept science at the next available
opportunity. The nominal plan is to intercept science at the beginning
of next week's SMS (Day 253).