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
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
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-V>0
~+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)
-
____________________________________________________________
Lynn F. Bassford
Hubble Space Telescope
CHAMP
Lockheed Martin
NASA GSFC PH#: 301-286-2876
"The Hubble Space Telescope is the
astronomical observatory and key to unlocking the most cosmic mysteries of the
past, present and future." - 7/26/6