Daily #3891

HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT # 3891

PERIOD COVERED: UT November 17, 2005 (DOY 321)

OBSERVATIONS SCHEDULED

ACS/HRC 10564

Resolving Ultracool White Dwarf Binaries

We propose an ACS/HRC imaging survey of the coolest white dwarfs known
in order to search for binarity. Current models fail to match observed
spectral energy distributions of these sub- 4000K stellar remnants,
consistently predicting much lower luminosities than observed. A
possible explanation is that they are binary in nature. Because these
cool degenerates have no spectral features, the only way to
investigate their apparent overluminosity is with very high resolution
imaging, which can only be done with HST {these stars are far too
faint to be observed with adaptive optics on the ground}. Optical
wavelengths are ideal because the spectral energy distributions of
these old degenerates peak near 600 nm. With the F435W filter we will
be able to partially resolve equally luminous binaries as close as
0.02", which corresponds to within 0.6 AU for over half of the 12
proposed target stars. The collected data will be critical in
determining whether these stars represent the oldest white dwarfs in
the solar neighborhood.

ACS/WFC 10586

The Rosetta Stone without a Distance: Hunting for Cepheids in the
Primordial Galaxy I Zw 18

The Blue Compact Dwarf galaxy I Zw 18 is one of the most intriguing
objects in the Local Universe. It has the lowest nebular metallicity
of all known galaxies {Z=1/32 solar}. It has long been regarded as a
possible example of a galaxy undergoing its first burst of star
formation. However, its real evolutionary state continues to be
controversial. The WFPC2 and NICMOS detection of AGB stars by our
group and others suggested the presence of an underlying older
population. However, deeper ACS observations by Izotov & Thuan {2004}
recently failed to detect the signature of RGB stars. This was
interpreted as confirmation that I Zw 18 is in fact a galaxy "in
formation", a local analog of primordial galaxies in the distant
Universe. This result was widely reported in the international news
media. However, an alternative possibility is that I Zw 18 is somewhat
further away than previously believed, so that Red Giant Branch stars
were too faint to detect. Quoted distances in the literature have
ranged from 10 to 20 Mpc. We intend to resolve this controversy by
direct determination of the distance to 1 Mpc accuracy using Cepheids.
For this we request 12 visits of two orbits each, to execute at
carefully planned intervals. We will obtain V and I band ACS/WFC
photometry in each visit. The new data will be combined with archival
data, but we show that the archival data by themselves are
insufficient to achieve our science goals. The distance will allow us
to place I Zw 18 into its proper place in the evolutionary sequence of
galaxy formation.

ACS/WFC 10592

An ACS Survey of a Complete Sample of Luminous Infrared Galaxies in
the Local Universe

At luminosities above 10^11.4 L_sun, the space density of far-infrared
selected galaxies exceeds that of optically selected galaxies. These
`luminous infrared galaxies' {LIRGs} are primarily interacting or
merging disk galaxies undergoing enhanced star formation and Active
Galactic Nuclei {AGN} activity, possibly triggered as the objects
transform into massive S0 and elliptical merger remnants. We propose
ACS/WFC imaging of a complete sample of 88 L_IR 10^11.4 L_sun
luminous infrared galaxies in the IRAS Revised Bright Galaxy Sample
{RBGS: i.e., 60 micron flux density 5.24 Jy}. This sample is ideal
not only in its completeness and sample size, but also in the
proximity and brightness of the galaxies. The superb sensitivity,
resolution, and field of view of ACS/WFC on HST enables a unique
opportunity to study the detailed structure of galaxies that sample
all stages of the merger process. Imaging will be done with the F439W
and F814W filters {B and I-band} to examine as a function of both
luminosity and merger state {i} the evidence at optical wavelengths of
star formation and AGN activity and the manner in which instabilities
{bars and bridges} in the galaxies may funnel material to these active
regions, {ii} the relationship between star formation and AGN
activity, and {iii} the structural properties {AGN, bulge, and disk
components} and fundamental parameters {effective radius and surface
brightness} of LIRGs and their similarity with putative evolutionary
byproducts {elliptical, S0 and classical AGN host galaxies}. This HST
survey will also bridge the wavelength gap between a Spitzer imaging
survey {covering seven bands in the 3.6-160 micron range} and a GALEX
UV imaging survey of these galaxies, but will resolve complexes of
star clusters and multiple nuclei at resolutions well beyond the
capabilities of either Spitzer or GALEX. The combined datasets will
result in the most comprehensive multiwavelength study of interacting
and merging galaxies to date.

ACS/WFC 10595

A Reference Database for Accurate Ages and Metallicities of Globular
Clusters in the Magellanic Clouds

We propose to finalize the compilation of a comprehensive database of
high-quality ages and metallicities of Simple Stellar Populations
{SSPs} in the Milky Way and the Magellanic Clouds. We will acquire new
ACS imagery for 8 young and intermediate-age globular clusters in the
Magellanic Clouds to create high-quality color-magnitude diagrams
{CMDs} to enable accurate measurements of their ages and
metallicities. In concert with a similar analysis of CMD data already
available in the HST archive for 8 more such GCs, the resulting
database will provide a well-sampled coverage of the full range of
ages and metallicities known among globular clusters {0.5 = Age {Gyr}
= 13.5 and -2.3 = [Fe/H] = +0.1, respectively}. This database will
form the crucial basis for our ongoing, comprehensive multi-wavelength
program to: {1} establish empirical relations among SSP colors {from
the UV [GALEX] through the mid-IR [Spitzer]}, line strengths, ages and
metallicities, and {2} provide a stringent test of the systemic
accuracy of age and metallicity determinations using state-of-the-art
population synthesis models.

ACS/WFC 10618

The Light Echoes around V838 Monocerotis: MHD in 3 Dimensions,
Circumstellar Mapping, and Dust

V838 Monocerotis, which burst upon the astronomical scene in early
2002, is a completely unanticipated new object. It underwent a
large-amplitude and very luminous outburst, during which its spectrum
remained that of an extremely cool supergiant. A rapidly evolving set
of light echoes around V838 Mon was discovered soon after the
outburst, and quickly became the most spectacular display of the
phenomenon ever seen. The light echoes, which were imaged by us with
HST during 2002, provide the means to accomplish four unique types of
measurements based on continued HST imaging during the event: {1}
Study effects of MHD turbulence at high resolution and in 3
dimensions; {2} Construct the first unambiguous and fully 3-D map of a
circumstellar dust envelope in the Milky Way; {3} Study dust physics
in a unique setting where the spectrum and light curve of the
illumination, and the scattering angle, are unambiguously known; and
{4} Determine the distance to V838 Mon through two independent direct
geometric techniques {polarimetry and angular expansion rates}.
Because of the extreme rarity of light echoes, this is almost
certainly the only opportunity to achieve such results during the
lifetime of HST. We propose a campaign during Cycle 14 of imaging the
echoes every 8 days for a total of 6 epochs, in order to fully map a
thin slab through the dust shell and achieve the other goals listed
above.

ACS/WFC/WFPC2 10585

NGC 4449: a Testbed for Starbursts in the Low- and High-Redshift
Universe

We will obtain deep ACS/WFC broad-band imaging in F435W, F555W, and
F814W of the Magellanic irregular galaxy NGC 4449 in order to infer
the properties of the resolved {young and old} stellar population,
compare the current strong star-formation activity to that at earlier
epochs, trace the major episodes of star formation over cosmic time,
and relate them to the past history of interaction/merging of this
galaxy. NGC 4449 is one of the closest { 5 Mpc} global starbursts
with a widespread star-formation activity that could have been
triggered by interaction or accretion. It is, therefore, the perfect
laboratory where to address issues related to star formation in
extreme environments and investigate processes connected to the
formation and evolution of galaxies in the early universe. At a
distance of 4.2 Mpc, the stellar content in NGC 4449 can easily be
resolved with HST. Yet, up to date no comprehensive dataset has been
collected that is suited to infer a global star-formation history of
the galaxy and to better understand its evolution. ACS/WFC provides
the angular resolution and sensitivity to easily reach magnitude
limits necessary for the detection of individual stars at the tip of
the red giant branch {i.e., with ages from 1 Gyr up to 12 Gyr} with
the required accuracy. A mosaic of 2 pointings along the major axis
will give a good coverage of the galaxy and will allow us to infer a
star- formation history unbiased by local properties of peculiar
regions. Narrow-band imaging in F658N {Halpha} will provide a map of
the ionized gas. Finally, WFPC2 parallel observations in F555W and
F814W will allow to search deep in the HI halo of NGC 4449 for
evidence of stars belonging to tidal streams. Our investigation of NGC
4449 will benefit from the wealth of observations already available
over almost the whole electromagnetic spectrum and will be crucial in
better understanding how starbursts can be influenced by merging
phenonema in both the low- and high-redshift universe.

FGS 10610

Astrometric Masses of Extrasolar Planets and Brown Dwarfs

We propose observations with HST/FGS to estimate the astrometric
elements {perturbation orbit semi-major axis and inclination} of
extra-solar planets orbiting six stars. These companions were
originally detected by radial velocity techniques. We have
demonstrated that FGS astrometry of even a short segment of reflex
motion, when combined with extensive radial velocity information, can
yield useful inclination information {McArthur et al. 2004}, allowing
us to determine companion masses. Extrasolar planet masses assist in
two ongoing research frontiers. First, they provide useful boundary
conditions for models of planetary formation and evolution of
planetary systems. Second, knowing that a star in fact has a plantary
mass companion, increases the value of that system to future
extrasolar planet observation missions such as SIM PlanetQuest, TPF,
and GAIA.

NIC1/NIC3 10726

NICMOS non-linearity tests

This program incorporates a number of tests to analyse the count rate
dependent non-linearity seen in NICMOS spectro-photometric
observations. In visit 1 we will observe a few fields with stars of a
range in luminosity in NGC1850 with NICMOS in NIC1 in F090M, F110W and
F160W and NIC2 F110W, F160W, and F180W. We will repeat the
observations with flatfield lamp on, creating artificially high
count-rates, allowing tests of NICMOS linearity as function of count
rate. To access the effect of charge trapping and persistence, we
first take darks {so there is not too much charge already trapped},
than take exposures with the lamp off, exposures with the lamp on, and
repeat at the end with lamp off. Finally, we continue with taking
darks during occultation. In visit 2 we will observe
spectro-photometric standard P041C using the G096 and G141 grisms in
NIC3, and repeat the lamp off/on/off test to artificially create a
high background. In visits 3&4 we repeat photometry measurements of
faint standard stars SNAP-2 and WD1657+343, on which the NICMOS
non-linearity was originally discovered using grism observations.
These measurements are repeated, because previous photometry was
obtained with too short exposure times, hence substantially affected
by charge trapping non-linearity. Measurements will be made with NIC1:
Visit 5 forms the persistence test of the program. The bright star
GL-390 {used in a previous persistence test} will iluminate the 3
NICMOS detectors in turn for a fixed time, saturating the center many
times, after which a series of darks will be taken to measure the
persistence {i.e. trapped electrons and the decay time of the traps}.
To determine the wavelength dependence of the trap chance, exposures
of the bright star in different filters will be taken, as well as one
in the G096 grism with NIC3. Most exposures will be 128s long, but two
exposures in the 3rd orbit will be 3x longer, to seperate the effects
of count rate versus total counts of the trap probability {in one
exposure, we get the full PSF worth of count rates, but we need a
longer exposure to separate the effect of rate versus total couts}.
Filters used: NIC1 F090M, F110W, F170M and F160W; NIC2 F110W, F160W,
F205W, F187W; NIC3 G096, F110W, F160W; 3x longer exposures: NIC1 and
NIC2 F110W.

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 08 08
FGS REacq 06 06
OBAD with Maneuver 28 28

SIGNIFICANT EVENTS: (None)