Daily Rpt #4406

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 # 4406

PERIOD COVERED: UT July 17, 2007 (DOY 198)

OBSERVATIONS SCHEDULED

ACS/WFC 10787

Modes of Star Formation and Nuclear Activity in an Early Universe
Laboratory

Nearby compact galaxy groups are uniquely suited to exploring the
mechanisms of star formation amid repeated and ongoing gravitational
encounters, conditions similar to those of the high redshift universe.
These dense groups host a variety of modes of star formation, and they
enable fresh insights into the role of gas in galaxy evolution. With
Spitzer mid-IR observations in hand, we have begun to obtain high
quality, multi-wavelength data for a well-defined sample of 12 nearby
{4500km/s} compact groups covering the full range of evolutionary
stages. Here we propose to obtain sensitive BVI images with the
ACS/WFC, deep enough to reach the turnover of the globular cluster
luminosity function, and WFPC2 U-band and ACS H-alpha images of
Spitzer- identified regions hosting the most recent star formation. In
total, we expect to detect over 1000 young star clusters forming
inside and outside galaxies, more than 4000 old globular clusters in
40 giant galaxies {including 16 early-type galaxies}, over 20 tidal
features, approximately 15 AGNs, and intragroup gas in most of the 12
groups. Combining the proposed ACS images with Chandra observations,
UV GALEX observations, ground-based H-alpha imaging, and HI data, we
will conduct a detailed study of stellar nurseries, dust, gas
kinematics, and AGN.

ACS/WFC/WFPC2 10904

Star formation in extended UV disk {XUV-disk} galaxies

The Galaxy Evolution Explorer {GALEX} has discovered the existence of
extended UV-disk {XUV-disk} galaxies. This class of intriguing spiral
galaxies is distinguished by UV-bright regions of star formation
located at extreme galactocentric radii, commonly reaching many times
the optical extent of each target. XUV-disks represent a population of
late-type galaxies still actively building, or significantly
augmenting, their stellar disk in the outer, low-density environment.
Prior to GALEX, such regions were considered to be far more stable
against star formation than now realized. Our work on these targets
has led to the recognition of the XUV phenomenon as probing a diverse
population of galaxies which, although having certain commonality in
terms of their present XUV star formation, have apparently experienced
different star formation histories {as judged by their outer disk
UV-optical colors and morphology}. In ordinary spirals, disk formation
occurred at a much earlier epoch, making today's XUV-disks useful
templates for commonplace, high z galaxies. The diverse XUV-disks in
our sample may represent snapshots of different phases in the disk
building process. We seek to characterize the demographics of star
forming regions occupying this environmental range, especially in
contrast to their inner disk counterparts. HST imaging is needed to
accurately characterize the massive stars and clusters which have, in
fact, managed to form. The GALEX observations are limited by 5"
resolution. Deep ACS FUV, B, V, I, and H-alpha imaging {along with
parallel WFPC2 data} will allow: {1} photometric classification of the
OB star population, {2} constraint on the cluster mass function and
age distribution, {3} critical accounting for possible leakage of
Lyman continuum photons in a porous ISM or an IMF change, and {4}
population synthesis modeling of the field SFH on Gyr timescales. We
benefit from extensive archival HST observations of our target
galaxies, although the outer disk has yet to be probed.

WFPC2 11105

The LBV progenitor of SN 2005gl - a new key to massive star evolution
puzzles

The currently accepted theory regarding the last stages of massive
star evolution maintains that the evolution of the envelope is coupled
to that of the stellar core. For this reason, very massive stars are
expected to shed their outer hydrogen envelopes before they develop
large iron cores, and ultimately, explode as core-collapse supernovae
{SNe}. It is therefore a strict prediction of current models that
massive stars {certainly those above ~40 solar mass} will explode as
hydrogen-poor SNe, i.e., of Types Ib and Ic. In particular, the class
of luminous blue variables {LBVs} such as eta-Carina, which are known
to be very massive {up to 100 solar masses and above} are expected to
lose their entire hydrogen envelopes prior to their ultimate
explosions as SNe. However, using pre-explosion HST/WFPC2 imaging of
the location of the recent hydrogen- rich type IIn SN 2005gl, we have
identified {Gal-Yam et al. 2007} its putative progenitor as a very
luminous point source {with absolute V magnitude of -10.2}. If this is
a single star, it must be an LBV from luminosity considerations {no
other stars are as luminous}. If our progenitor identification is
correct, at least in some cases, massive stars explode before losing
most of their hydrogen envelope, indicating the core and envelope are
decoupled, and requiring revision of stellar evolution theory. Here,
we propose a single-orbit HST observation of the location of SN 2005gl
designed to test whether the point source we identified as its LBV
progenitor has indeed disappeared {as expected from a single star} or
remained unchanged {as expected, e.g., if it is a compact star
cluster}. These data are the last observational ingredient required to
firmly establish {or refute} the explosion of an LBV as a type IIn SN,
with fundamental implications for the theory of massive star
evolution. Since the new data will be compared to pre-explosion WFPC2
images, this program is perfectly suited to be carried out with the
WFPC2 camera.

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 11218

Snapshot Survey for Planetary Nebulae in Globular Clusters of the
Local Group

Planetary nebulae {PNe} in globular clusters {GCs} raise a number of
interesting issues related to stellar and galactic evolution. The
number of PNe known in Milky Way GCs, 4, is surprisingly low if one
assumes that all stars pass through a PN stage. However, it is likely
that the remnants of stars now evolving in Galactic GCs leave the AGB
so slowly that any ejected nebula dissipates long before the star
becomes hot enough to ionize it. Thus there should not be ANY PNe in
Milky Way GCs--but there are four! It has been suggested that these
PNe are the result of mergers of binary stars within GCs, i.e., that
they are descendants of blue stragglers. The frequency of occurrence
of PNe in external galaxies poses more questions, because it shows a
range of almost an order of magnitude. I propose a Snapshot survey
aimed at discovering PNe in the GC systems of Local Group galaxies
more distant than the Magellanic Clouds. These clusters, some of which
may be much younger than their counterparts in the Milky Way, might
contain many more PNe than those of our own galaxy. I will use the
standard technique of emission-line and continuum imaging, which
easily discloses PNe.

WFPC2 11223

The Key to Understanding RR Lyr Stars: WFPC2 Observations of a Unique
LMC EB with a RR Lyr Component

We are proposing HST/WFPC2 2550-10420A multi-band photometry of an
important "unique" LMC eclipsing binary with an RR Lyr component. This
binary is the only bona fide eclipsing binary {EB} with an RR Lyr
component. Because of their constant mean luminosities {L ~ 45 Lsun;
Mv ~ +0.5 mag} and easily recognizable light curves, RR Lyr
variables have long served as the "cornerstone" of the Pop II distance
scale in our galaxy and for Local Group galaxies. However, in spite of
their critical importance to astronomy, there is a paucity of
fundamental data available for RR Lyr stars. In fact, there are no
direct measures of their most fundamental properties - such as Mass,
Radius and Luminosity. The astrophysical and cosmological consequences
of finding an RR Lyr star in an EB are considerable, because the
masses and absolute radii of the stars of eclipsing binaries can be
determined to within a few percent from time-tested analyses of their
light and radial velocity curves. With accurate temperatures and ISM
absorption values, determined from the proposed WFPC2 observations, it
is possible to determine reliable stellar luminosities and distances.
It is for these reasons that we propose WFPC2 observations of the
recently discovered detached LMC eclipsing binary OGLE
J052218.07-692827.4 {V ~18.6- mag; B-V0 ~+0.27; Porb = 8.9231-d};
the RR Lyr primary component has a pulsation period of P{RR} =
0.564876-d. This important binary star is an integral part of our
on-going multi- wavelength study of selected eclipsing binaries in
nearby galaxies. Three HST/WFPC2 orbits are requested to determine
complementary accurate Teff, log g and ISM absorption {A-lambda} for
the component stars. These quantities will be combined with the
fundamental stellar data being determined from our ground-based radial
velocity and photometric observations. The combined observations will
yield accurate stellar masses, radii, temperatures and luminosities,
as well as a direct distance to the binary and LMC-Bar. This RR Lyr/EB
thus offers the unprecedented opportunity to: {1} determine directly
{and for the first time} the fundamental physical properties {M, R, L}
of an RR Lyr star, {2} directly calibrate "in situ" the zero-point of
the LMC RR Lyr - P - Mv - Z relation and {3} to derive an additional
accurate distance to the Bar region of the LMC.

WFPC2 11293

The Dynamical Mass of the Bright Cepheid Polaris

Cepheid variables are of central importance in Galactic and
extragalactic astronomy. They are the primary standard candles for
measuring extragalactic distances, and they provide critical tests of
stellar-evolution theory. Surprisingly, however, until now there was
not a single Cepheid with a purely dynamical measurement of its mass.
Polaris {alpha UMi} is the nearest and brightest of all Cepheids. It
offers the unique opportunity to measure the dynamical mass of a
Cepheid, because it is in a binary system for which a single-lined
spectroscopic orbit is already available. In Cycle 14, we resolved the
system in the UV using ACS/HRC, thus providing the first direct
detection of the companion, as well as a first approximation to the
dynamical mass. In the present proposal we request one HST orbit per
year for the next 3 Cycles, in order to refine the visual orbit.
Combined with the HST/FGS parallax {see below}, this program will
provide an accurate mass for the Cepheid {the error should be about
0.5 Msun by Cycle 17}, and the only one based purely on dynamical
information. Only HST's combination of high spatial resolution and UV
sensitivity can achieve this result. The parallax is a key ingredient
in the mass determination. In an ongoing multi-year program {GO-9888,
GO-10113, GO-10482}, we are using the FGS to improve significantly
upon the Hipparcos parallax of Polaris. The WFPC2 imaging proposed
here is a continuation of our program initiated with the ACS. These
observations will provide extremely valuable astrophysical information
from a very modest additional investment of observing time.

FLIGHT OPERATIONS SUMMARY:

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

HSTARS:

#10898 - GSAcq (1,2,1) failed to RGA hold (Gyro Control).

Upon acquisition of signal (AOS) at 198/17:38:14, the GSAcq(1,2,1)
scheduled at 198/17:27:23 - 17:35:14 had failed to RGA Hold due to
(QF1STOPF) stop flag indication on FGS-1. Pre-acquisition OBADs
attitude correction values not available due to LOS. Post-acq OBAD/MAP
had (RSS) value of 18.16 arcseconds.

#10899 - REacq(2,1,2) failed, Search Radius Limit exceeded on FGS 2.

Upon acquisition of signal at 198/22:41:27 vehicle was in gyro
control, REacq(2,1,2) at 22:14:25 failed with search radius limit
exceeded on FGS 2. OBAD prior to GSACQ at 22:10:05 had RSS error of
18.01 arcseconds.

COMPLETED OPS REQUEST: (None)

******************************* SCHEDULED SUCCESSFUL
FGS GSacq********************** 06************ 05
FGS REacq********************** 06************ 05
OBAD with Maneuver******* ***** 24************* 24

COMPLETED OPS NOTES: (None)

SIGNIFICANT EVENTS: (None)