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Daily #4032



 
 
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Old January 20th 06, 04:11 PM posted to sci.astro.hubble
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Default Daily #4032

HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT #4032

PERIOD COVERED: UT January 19, 2006 (DOY 019)

OBSERVATIONS SCHEDULED

ACS/HRC 10542

Charting the Sparkling Star Formation in NGC346

New, stunning V, I images of the youngest and most massive star
forming region NGC 346, in the Small Magellanic Cloud, have been
recently obtained with the HST/ACS. They reveal a myriad of small
compact clusters: some are still embedded in dust, possibly connected
by gas and dust filaments. We also discover a rich population of
pre-main sequence low mass stars {~3 -0.6 Mo} mainly distributed in
the body of NGC 346 and in these compact clusters, which formed with
the central cluster {~5My ago}, but have not reached the main sequence
yet. The immediate question that emerges is: how did star formation
occur in this region? Is there evidence for an age spread among these
clusters, that could be indicative of sequential star formation? We
are, therefore, requesting an immediate follow up investigation with
the ACS/HRC to perform a comprehensive UV/U study of the ten largest
clusters identified in the NGC 346 region, with the objective of
determining, in combination with the already available deep V, I data,
their mass function, their upper mass cut-off, whether mass
segregation is present, whether there are age variations, and what is
the impact of the stellar feedback, with the final aim to establish
how star formation has occured and progressed in this low metallicity
environment.

ACS/HRC 10559

Astrometric monitoring of binary L and T dwarfs

We propose to obtain high angular resolution ACS images of five binary
L and T dwarfs in order to determine their orbital parameters and
dynamical masses, and directly constrain the evolutionary models of
ultracool and substellar objects. The binaries have estimated periods
ranging between 5 and 14 years. All of them have already been resolved
at least twice {sometimes more} using HST, providing first and second
epochs measurements. We propose to obtain two more ACS imaging
observations separated by 9 to 12 months during cycle 14. The expected
period coverage should therefore range between 35% and 117%, allowing
us to compute precise orbital parameters and masses. Our sample is
large enough and covers a sufficiently wide range of spectral types
{from L3 to T5.5} to allow us to obtain strong constraints the
evolutionnary models.

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/HRC/WFC 10514

Kuiper Belt Binaries: Probes of Early Solar System Evolution

Binaries in the Kuiper Belt are a scientific windfall: in them we have
relatively fragile test particles which can be used as tracers of the
early dynamical evolution of the outer Solar System. We propose a
Snapshot program using the ACS/HRC that has a potential discovery
efficiency an order of magnitude higher than the HST observations that
have already discovered the majority of known transneptunian binaries.
By more than doubling the number of observed objects in dynamically
hot and cold subpopulations we will be able to answer, with
statistical significance, the question of whether these groups differ
in the abundance of binaries as a result of their particular dynamical
paths into the Kuiper Belt. Today's Kuiper Belt bears the imprints of
the final stages of giant-planet building and migration; binaries may
offer some of the best preserved evidence of that long-ago era.

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.

WFPC2 10777

WFPC2 WF4 Bay 1 Temperature Reduction Test #1

This proposal tests methods to improve WF4 bias level stability by
adjusting some temperatures inside WFPC2. 1 external and 24 internal
orbits.

FLIGHT OPERATIONS SUMMARY:

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

HSTARS:

10091 - GSAcq (1,2,2) failed to RGA control (T2G) due to Search Radius
Limit Exceeded on FGS 1 @ 019/0959z

GSAcq (1,2,2) scheduled at 019/09:59:53 falied due to search radius
limit exceeded on FGS 1. ESB 1902 (OBAD Failed Identification) was
received. ESB a05 (FGS Coarse Trac Failed-Search Radius Limit
Exceeded) was received, also 3 ESB 1805's were received.

OBAD 1 = V1 716.06, V2 -505.87, V3 - 203.06, RSS 899.93

OBAD 2 = V1 11760.04, V2 -492.93, V3 50827.72, RSS 52172.78

OBAD Map showed the following errors: V1 -4.62, V2 -244.50, V3 -1.22, RSS
244.55

COMPLETED OPS REQUEST: (None)

COMPLETED OPS NOTES: (None)

SCHEDULED SUCCESSFUL FAILURE TIMES
FGS GSacq 07 06 019/0959z
(HSTAR 10091)
FGS REacq 08 08
OBAD with Maneuver 29 28 019/0957z
(HSTAR 10091)

SIGNIFICANT EVENTS: (None)


 




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