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Daily #4037

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Old January 27th 06, 01:28 PM posted to sci.astro.hubble
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Default Daily #4037

HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science


PERIOD COVERED: UT January 26, 2006 (DOY 026)


ACS/HRC 10512

Search for Binaries Among Faint Jupiter Trojan Asteroids

We propose an ambitious SNAPSHOT program to survey faint Jupiter
Trojan asteroids for binary companions. We target 150 objects, with
the expectation of acquiring data on about 50%. These objects span
Vmag = 17.5-19.5, a range inaccessible with ground-based adaptive
optics. We now have a significant sample from our survey of brighter
Trojans to suggest that the binary fraction is similar to that which
we find among brighter main-belt asteroids, roughly 2%. However, our
observations suggest a higher binary fraction for smaller main-belt
asteroids, probably the result of a different formation mechanism
{evident also from the physical characteristics of the binaries}.
Because the collision environment among the Trojans is similar to that
of the Main Belt, while the composition is likely to be very
different, sampling the binary fraction among the fainter Trojans
should help us understand the collisional and binary formation
mechanisms at work in various populations, including the Kuiper Belt,
and help us evaluate theories for the origin of the Trojans.
Calibration of and constraints on models of binary production and
collisional evolution can only be done using these large-scale,
real-life physical systems that we are beginning now to find and

ACS/HRC 10553

Bipolar Scattering Structures in AGN

The Unified Scheme for Seyfert galaxies successfully explains the
basic distinctions between Type 1 and Type 2 AGN, including the
existence of broad scattered lines in polarized flux spectra of the
latter. However, it fails to account for the strongly polarized broad
lines often observed in Type 1 AGN. We have discovered an intermediate
type red QSO that exhibits polarization properties of both types;
indeed it suggests a bipolar scattering geometry similar to that seen
in Galactic protoplanetary nebulae. We request a small allocation with
the high- resolution camera on ACS to image the object in two key
spectral bands. The results will allow an unambiguous interpretation
of ground-based data, and enable modeling of the inclination and
opening angle that illuminates the scattering clouds. Like NGC 1068, a
successful explanation of this object will not only allow further
unification of AGN but also aid in unraveling the details of their
inner structure.

ACS/HRC 10609

Sizes, Shapes, and SEDs: Searching for Mass Segregation in the Super
Star Clusters of Nearby Starburst

We propose to investigate mass segregation and star cluster evolution
and dissolution processes in Super Star Cluster {SSC} populations in a
small sample of nearby starburst galaxies. ACS/HRC and NICMOS images
of these nearby {d 10 Mpc} starbursts can reveal evidence for mass
segregation in the form of variations in size, shape, and color of the
SSCs as a function of wavelength. The compactness of the cluster light
profiles, and hence the stellar mass distributions, is a critical
indicator of the likely fate of an SSC: long life and eventual
evolution into a globular-like cluster, or dissolution. These
observations will allow us to generate spectral energy distributions
{SEDs} for a large sample of the SSCs at all ages and extinctions in
each system. We will combine the SEDs with population synthesis models
and existing ground- based spectra and Spitzer images to estimate
ages, reddenings, and masses thus derive a more complete picture of
the star-formation histories of the galaxies. For the brightest and
most likely virialized among the SSCs we will also constrain their
initial mass functions {IMFs} using high- resolution spectroscopy.
Conclusions about IMFs from this technique require detailed
information about the SSC concentration, light profiles, and virial
status, which are only possible via ACS data. The proposed
observations will provide an extensive and comprehensive data set for
a large number of SSCs. By addressing the issues of mass segregation,
evaporation, and destruction of SSC populations, the proposed
observations will provide strong constraints on theories regarding the
processes involved in the formation and evolution of SSCs and globular
clusters. Given the dire predictions for the lifetime of HST, and its
tremendous impact on the study of SSCs, we feel that the proposed
observations not only are necessary and timely {even urgent} but will
also be a fitting { and possibly final} addition to HST's legacy in
the study of starburst SSCs.


Near-UV Snapshot Survey of Low Luminosity AGNs

Low-luminosity active galactic nuclei {LLAGNs} comprise ~30% of all
bright galaxies {B12.5} and are the most common type of AGN. These
include low-luminosity Seyfert galaxies, LINERs, and transition-type
objects {TOs, also called weak-[OI] LINERs}. What powers them is still
at the forefront of AGN research. To unveil the nature of the central
source we propose a near-UV snapshot survey of 50 nearby LLAGNs using
ACS/HRC and the filter {F330W}, a configuration which is optimal to
detect faint star forming regions around their nuclei. These images
will complement optical and near-IR images available in the HST
archive, providing a panchromatic atlas of the inner regions of these
galaxies, which will be used to study their nuclear stellar
population. Our main goals are to: 1} Investigate the presence of
nuclear unresolved sources that can be attributed to an AGN; 2}
Determine the frequency of nuclear and circumnuclear stellar clusters,
and whether they are more common in Transition Objects {TOs} than in
LINERs; 3} Characterize the sizes, colors, luminosities, masses and
ages of these clusters; 4} Derive the luminosity function of star
clusters and study their evaporation over time in the vicinity of
AGNs. Finally, the results of this project will be combined with those
of a previous similar one for Seyfert galaxies in order to compare the
nature of the nuclear sources and investigate if there could be an
evolution from Seyferts to TOs and LINERs. By adding UV images to the
existing optical and near-IR ones, this project will also create an
extremely valuable database for astronomers with a broad range of
scientific interests.

ACS/WFC 10491

A Snapshot Survey of the most massive clusters of galaxies

We propose a snapshot survey of a sample of 124 high X-ray luminosity
clusters in the redshift range 0.3-0.7. Similarly luminous clusters at
these redshifts frequently exhibit strong gravitational lensing. The
proposed observations will provide important constraints on the nature
of the cluster mass distributions and a set of optically bright,
lensed galaxies for further 8-10m spectroscopy. We acknowledge the
broad community interest in this sample and waive our data rights for
these observations.

ACS/WFC 10520

Resolving the Complex Star Formation History of the Leo I Dwarf
Spheroidal Galaxy

Determining the star formation histories {SFHs} and chemical evolution
of nearby galaxies gives us powerful constrains on the physical
processes that regulate galaxy evolution. The SFHs can be measured
most accurately by comparing the observed densities of stars in
color-magnitude diagrams {CMDs} to predictions from stellar
evolutionary models. WFPC2 imaging of the Leo I dSph shows it is
unique because its stellar population is relatively young.
Approximately 68% of its stars formed between 1 and 7 Gyr ago and only
12% of its stars formed ~ 10 Gyr ago. We propose to vastly improve
the derived SFH of Leo I by exploiting ACS/WFC's higher quantum
efficiency at bluer wavelengths, higher spatial resolution, and larger
field-of-view. The figure of merit for our proposed observations,
defined as the age resolution times the number of stars detected, will
be a factor of 12 higher than existing WFPC2 observations. To surmount
the degeneracy of age and metallicity in the CMD, we have
independently measured the metallicity distribution of its stars using
spectroscopy. Simultaneously modeling the metallicity distribution and
CMD, we will firmly constrain the evolution of the Leo I dSph, a
unique example of an isolated dwarf galaxy that has not been
influenced by interactions with the Milky Way or M31.

ACS/WFC 10543

Microlensing in M87 and the Virgo Cluster

Resolving the nature of dark matter is an urgent problem. The results
of the MACHO survey of the Milky Way dark halo toward the LMC indicate
that a significant fraction of the halo consists of stellar mass
objects. The VATT/Columbia survey of M31 finds a similar lens fraction
in the M31 dark halo. We propose a series of observations with ACS
that will provide the most thorough search for microlensing toward
M87, the central elliptical galaxy of the Virgo cluster. This program
is optimized for lenses in the mass range from 0.01 to 1.0 solar
masses. By comparing with archival data, we can detect lenses as
massive as 100 solar masses, such as the remnants of the first stars.
These observations will have at least 15 times more sensitivity to
microlensing than any previous survey, e.g. using WFPC2. This is due
to the factor of 2 larger area, factor of more than 4 more sensitivity
in the I-band, superior pixel scale and longer baseline of
observations. Based on the halo microlensing results in the Milky Way
and M31, we might expect that galaxy collisions and stripping would
populate the overall cluster halo with a large number of stellar mass
objects. This program would determine definitively if such objects
compose the cluster dark matter at the level seen in the Milky Way. A
negative result would indicate that such objects do not populate the
intracluster medium, and may indicate that galaxy harassment is not as
vigorous as expected. We can measure the level of events due to the
M87 halo: this would be the best exploration to date of such a lens
population in an elliptical galaxy. Star-star lensing should also be
detectable. About 20 erupting classical novae will be seen, allowing
to determine the definitive nova rate for this giant elliptical
galaxy. We will determine if our recent HST detection of an M87
globular cluster nova was a fluke, or indicative of a 100x higher rate
of incidence of cataclysmic variables and nova eruptions in globulars
than previously believed. We will examine the populations of variable
stars, and will be able to cleanly separate them from microlensing.

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


Probing Evolution And Reionization Spectroscopically {PEARS}

While imaging with HST has gone deep enough to probe the highest
redshifts, e.g. the GOODS survey and the Ultra Deep Field,
spectroscopic identifications have not kept up. We propose an ACS
grism survey to get slitless spectra of all sources in a wide survey
region {8 ACS fields} up to z =27.0 magnitude, and an ultradeep field
in the HUDF reaching sources up to z =28 magnitude. The PEARS survey
will: {1} Find and spectrocopically confirm all galaxies between
z=4-7. {2} Probe the reionization epoch by robustly determining the
luminosity function of galaxies and low luminosity AGNs at z = 4 - 6.
With known redshifts, we can get a local measure of star formation and
ionization rate in case reionization is inhomogeneous. {3} Study
galaxy formation and evolution by finding galaxies in a contiguous
redshift range between 4 z 7, and black hole evolution through a
census of low-luminosity AGNs. {4} Get a robust census of galaxies
with old stellar populations at 1 z 2.5, invaluable for checking
consistency with heirarchical models of galaxy formation. Fitting
these galaxies' spectra will yield age and metallicity estimates. {5}
Study star-formation and galaxy assembly at its peak at 1 z 2 by
identifying emission lines in star-forming galaxies, old populations
showing the 4000A break, and any combination of the two. {6} Constrain
faint white dwarfs in the Galactic halo and thus measure their
contribution to the dark matter halo. {7} Derive spectro-photometric
redshifts by using the grism spectra along with broadband data. This
will be the deepest unbiased spectroscopy yet, and will enhance the
value of the multiwavelength data in UDF and the GOODS fields to the
astronomical community. To this end we will deliver reduced spectra to
the HST archives.


NICMOS Post-SAA calibration - CR Persistence Part 1.

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.


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


10107 - REacq(2,1,1) failed due to search radius limit exceeded. @

Reacq(2,1,1) scheduled at 027/09:40:28 failed due to search radius
limit exceeded on FGS 2 at 09:45:12. A ESB a05 was received. The Map
at 09:47:21 showed errors of V1=2.67, V2=86.92, V3=5.13, RSS=87.11.
OBAD2 before the reacq showed errors of V1=10.58, V2=48.40, V3=10.99,



FGS GSacq 10 10
FGS REacq 04 03 Hstar #
OBAD with Maneuver 24 24



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