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Daily # 3956



 
 
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Old September 16th 05, 04:04 PM
Joe Cooper
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Default Daily # 3956

HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT # 3946

PERIOD COVERED: UT September 15, 2005 (DOY 258)

OBSERVATIONS SCHEDULED

ACS/HRC 10377

ACS Earth Flats

High signal sky flats will be obtained by observing the bright Earth
with the HRC and WFC. These observations will be used to verify the
accuracy of the flats currently used by the pipeline and will provide
a comparison with flats derived via other techniques: L-flats from
stellar observations, sky flats from stacked GO observations, and
internal flats using the calibration lamps. Weekly coronagraphic
monitoring is required to assess the changing position of the spots.

ACS/HRC/WFC 10487

A Search for Debris Disks in the Coeval Beta Pictoris Moving Group

Resolved observations of debris disks present us with the opportunity
of studying planetary evolution in other solar systems. We propose to
search for debris disks in the Beta Pictoris moving group {8-20 Myrs,
10-50 pc away} , which provides a coeval sample of multiple spectral
types, and it has already produced two magnificent resolved debris
disks: AU Mic and Beta Pic. Such coeval sample will provide us with a
snapshop of the crucial time in disk evolution in which the disk makes
the transition from optically thick to optically thin, and it will be
useful to study the stellar mass dependence of the disk evolution.

ACS/WFC 10505

The Onset of Star Formation in the Universe: Constraints from Nearby
Isolated Dwarf Galaxies.

The details of the early star formation histories of tiny dwarf
galaxies can shed light on the role in galaxy formation of the
reionization which occured at high redshift. Isolated dwarfs are ideal
probes since their evolution is not complicated by environmental
effects owing to the vicinity of the Milky Way and M31. In addition,
dwarf galaxies are the most common type of galaxies, and potentially
the building blocks of larger galaxies. Since we can date the oldest
stars in them, their study represents a complementary approach to the
study of the formation and evolution of galaxies through high-z
observations. We propose to use the ACS to obtain a homogeneus dataset
of high-quality photometry, down to the old {13 Gyr} main-sequence
turnoffs, for a representative sample of 4 isolated Local Group dwarf
galaxies. These data are essential to unambiguously determine their
early star formation histories, through comparison with synthetic
color-magnitude diagrams, and using the constraints provided by their
variable stars. Parallel WFPC2 observations of their halos will allow
us to reveal the actual nature of their stellar population gradients,
providing important aditional constraints on their evolution. The
proposed observations are being complemented with ground-based
spectroscopy, to obtain metallicity and kinematic information. The
observations requested here, which must reach M_I=+3.5 {I=27.5- 28.2}
with S/N=10 in crowded systems, can only be achieved with HST using
ACS. Based on deep WFPC2 observations and ACS image simulations, our
team has designed an observational strategy which carefully considers
the optimal filter combination, the necessary photometry depth and the
effects of stellar crowding.

ACS/WFC 10524

Blue Stragglers: a key stellar population to probe internal cluster
dynamics

This proposal is part of a coordinated project devoted to understand
the interplay of globular cluster {GC} dynamics and the formation and
evolution of blue straggler stars {BSS}. By using a combination of HST
and ground-based observations we are constructing complete BSS surveys
in a sample of GCs; complete BSS surveys require mid-UV HST
observations in the center and wide field CCD ground based
observations under excellent seeing conditions of the exterior. Up to
now only four clusters have been surveyed in this way and the results
are surprising: in three GCs {M3, 47 Tuc, NGC 6752} we have discovered
that the BSS radial distribution is bimodal, highly peaked in the
cluster center, rapidly decreasing at intermediate radii and rising
again at large radii {Ferraro et al. 1997, 2004, Sabbi et al. 2004},
conversely BSS population in Omega Centauri does not show any
signature of the segregation which would be expected for a class of
objects arising from either stellar interactions or binarity {Ferraro
et al. 2005}. These observational facts are opening a new prospective
in the study of the formation processes and evolution of BSS in GCs.
By using extensive simulations, we demonstrated that the spatial
distribution of BSS observed in 47 Tuc can be only reproduced if a
sizable fraction of BSS is generated {via mass transfer in primordial
binaries} in the peripheral region of the cluster {Mapelli et al
2004}, thus excluding a purely collisional formation scenario. Here we
propose mid-UV imaging of a few clusters suspected of harboring a
large population of central BSS and a few known to have many BSS the
external region. These are good candidates for determining accurate
BSS radial distributions. The modest amount of time proposed here will
go far to determine the ubiquity of BSS bimodality and to constrain
models of dynamical evolution. Since we believe the proposed
observations would be useful to the entire stellar community {for
multifold purposes} we waive the propretary period.

ACS/WFC 10526

Dynamics of the Polarization Structure of the Crab Nebula

The Crab Nebula is not a free expansion SNR. Rather, it is a pulsar
wind nebula expanding from the inside out into a larger remnant of
freely expanding ejecta. At the heart of this object is the Crab
Pulsar and the region where the pulsar's highly nonisotropic wind
interacts with the larger synchtron nebula. HST and Chandra monitoring
has shown this to be one of the most intricately structured and highly
dynamical objects ever observed. In Cycle 12 we demonstrated our
ability to use the polarization capabilities of the ACS to isolate
physically discrete features within the Crab Synchrotron Nebula and
accurately measure their polarization characteristics. These data
provide a unique look at the physical structure in the heart of the
Crab, adding a new dimension to past observations. Polarization
provides extensive information about field geometries, the degree of
disorder in the field, and particle pitch angle distributions. But one
image of the Crab is like a single image of waves at the beach. It
necessarily misses the point. In the Crab, the name of the game is
"dynamics". In this proposal we request time to monitor changes in the
polarization structure of the Crab. This program will allow us to
follow the changing polarization of features including
relativistically moving wisps in the Crab Nebula. This is the only
place in the sky where a dynamic relativistic plasma can be observed
in sufficient detail to make such measurements possible, and the
HST/ACS is the only instrument that we are likely to see in our
careers capable of making the measurement. These observations will be
an important addition to the already rich observational legacy of HST
for what is arguably the most important single object in astrophysics.

NIC1/NIC2/NIC3 8793

NICMOS Post-SAA calibration - CR Persistence Part 4

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. The keyword 'USEAFTER=date/time' will also be added to
the header of each POST-SAA DARK frame. The keyword must be populated
with the time, in addition to the date, because HST crosses the SAA ~8
times per day so each POST-SAA DARK will need to have the appropriate
time specified, for users to identify the ones they need. Both the raw
and processed images will be archived as POST-SAA DARKSs. Generally we
expect that all NICMOS science/calibration observations started within
50 minutes of leaving an SAA will need such maps to remove the CR
persistence from the science images. Each observation will need its
own CRMAP, as different SAA passages leave different imprints on the
NICMOS detectors.

NIC2 10603

Multiwavelength Imaging of Edge-on Protoplanetary Disks: Quantifying
the Growth of Circumstellar Dust

Young, edge-on circumstellar disks are uniquely valuable laboratories
for the study of planet formation. In these objects, the central star
is occulted from direct view, significant PSF artifacts are absent,
and the disk is clearly seen as a central dust lane flanked by faint
disk reflected light. The detailed morphology of these nebulae and its
variation with wavelength provide crucial information on the disk
internal structure and the properties of its constituent dust grains.
A key observable is the slope defining the wavelength dependence of
the dust scattering opacity, which becomes shallower when grain growth
has taken place; multiwavelength resolved disk images are the key
dataset enabling such measurements. Recent analyses of three different
edge-on disks have revealed a diversity in their dust properties that
is indicative of different degrees of dust grain evolution having
taken place in each system. This characterization of disk grain
growth, when applied comparatively to a larger sample of these
objects, would enable the construction of an evolutionary sequence of
young disks at successive stages on the road to planet formation. In
pursuit of this goal, we have identified a sample of 15 edge-on disks
previously discovered by HST or groundbased telescopes, but for which
high fidelity, high spatial resolution images do not yet exist in both
the optical and near-infrared. We propose broad-band multicolor
imaging with NICMOS of all these targets, and ACS imaging of nine of
these targets In combination with existing data, the proposed images
will form a complete database of high resolution optical/near-IR
images for these 15 disk systems. Scattered light modeling will be
used to derive the disk structure and dust properties, yielding
results that will be of fundamental importance for our understanding
of grain properties during protoplanetary disk evolution.

FLIGHT OPERATIONS SUMMARY:

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

HSTARS:

9951 - GSAcq(2,3,2) failed to RGA Control (T2GAttHd) @ 258/08:10z The
GSAcq(2,3,2) scheduled at 258/08:10:00 - 08:17:18 failed to RGA
Control (T2GAttHd) due to search radius limit exceeded on FGS-2. 486
ESB "a05" search rad lmt exc was received at 258/08:14:50. Prior FHST
OBAD1 (with maneuver)scheduled at 258/07:53:21 showed vehicle axis
errors: V1=-40.42, V2=-1892.64, V3=2065.24. 3ax-s (RSS)
value=2801.62 arcsec. Prior FHST OBAD2 (with maneuver) scheduled at
258/08:04:44 showed vehicle axis erros: V1=-3.34, V2=32.36, V3=71.60.
3-axis (RSS) value=78.65 arcsec. Subsequent FHST OBAD (but no
maneuver) scheduled at 258/08:17:18 showed vehicle axis errors:
V1=115.07, V2=-657.11, V3=-812.71. 3-axis (RSS) value =1051.44 arcsec.

9953 - GSACQ(2,1,2) failed, search radius limit exceeded on FGS 1 @
258/10:30:25z GSACQ(2,1,2) at 258/10:26:11 failed due to Search Radius
Limit Exceeded on FGS 1 at 10:30:25. OBAD prior to GSACQ had total RSS
attitude error of 5.14 arcseconds, well within the search radius.
GSACQ(2,1,2) at 12:02:09 with the same guide stars was successful.

COMPLETED OPS REQUEST: (None)

COMPLETED OPS NOTES: (None)

SCHEDULED SUCCESSFUL FAILURE TIMES
FGS Gsacq 08 06 HSTAR
9951,9953
FGS Reacq 06 06
OBAD with Maneuver 28 28


SIGNIFICANT EVENTS: (None)


 




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