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Daily Report # 4363



 
 
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Old May 16th 07, 04:04 PM posted to sci.astro.hubble
Cooper, Joe
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Posts: 568
Default Daily Report # 4363

Notice: For the foreseeable future, the daily reports may contain apparent
discrepancies between some proposal descriptions and the listed instrument
usage. This is due to the conversion of previously approved ACS WFC or HRC
observations into WFPC2, or NICMOS observations subsequent to the loss of
ACS CCD science capability in late January.


HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT # 4363

PERIOD COVERED: UT May 15, 2007 (DOY 135)

OBSERVATIONS SCHEDULED

WFPC2 10800

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 to continue a
Snapshot program using the ACS/HRC that has a demonstrated discovery
potential an order of magnitude higher than the HST observations that have
already discovered the majority of known transneptunian binaries. With this
continuation we seek to reach the original goals of this project: to
accumulate a sufficiently large sample in each of the distinct populations
collected in the Kuiper Belt to be able to measure, with statistical
significance, how the fraction of binaries varies as a function 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.

WFPC2 10832

Solving the microlensing puzzle: An HST high-resolution imaging approach

We propose to use the HST Advanced Camera for Surveys High Resolution
Channel to obtain high resolution imaging data for 10 bona-fide LMC
microlensing events seen in the original MACHO survey. The purpose of this
survey will be to assess whether or not the lens and source stars have
separated enough to be resolved since the original microlensing event took
place - about a decade has passed since the original MACHO survey and the
HST WFPC2 follow-up observations of the microlensing events. If the
components of the lensing event are resolved, we will determine the apparent
magnitude and color of both the lens and the source stars. These data, in
combination with Spitzer/IRAC data and Magellan near-IR JHK data, will be
used to ascertain the basic properties of the lens stars. With the majority
of the microlensing events in the original MACHO survey observed at the
highest spatial resolution currently possible, we will be able to draw
important conclusions as to what fraction of these events have lenses which
belong to some population of dwarf stars in the disk and what fraction must
be due to lenses in the halo or beyond. These data will greatly increase our
understanding of the structure of the Galaxy by characterizing the stellar
population responsible for the gravitational microlensing.

ACS/SBC 10862

Comprehensive Auroral Imaging of Jupiter and Saturn during the International
Heliophysical Year

A comprehensive set of observations of the auroral emissions from Jupiter
and Saturn is proposed for the International Heliophysical Year in 2007, a
unique period of especially concentrated measurements of space physics
phenomena throughout the solar system. We propose to determine the physical
relationship of the various auroral processes at Jupiter and Saturn with
conditions in the solar wind at each planet. This can be accomplished with
campaigns of observations, with a sampling interval not to exceed one day,
covering at least one solar rotation. The solar wind plasma density
approaching Jupiter will be measured by the New Horizons spacecraft, and a
separate campaign near opposition in May 2007 will determine the effect of
large-scale variations in the interplanetary magnetic field {IMF} on the
Jovian aurora by extrapolation from near-Earth solar wind measurements. A
similar Saturn campaign near opposition in Jan. 2007 will combine
extrapolated solar wind data with measurements from a wide range of
locations within the Saturn magnetosphere by Cassini. In the course of
making these observations, it will be possible to fully map the auroral
footprints of Io and the other satellites to determine both the local
magnetic field geometry and the controlling factors in the electromagnetic
interaction of each satellite with the corotating magnetic field and plasma
density. Also in the course of making these observations, the auroral
emission properties will be compared with the properties of the near-IR
ionospheric emissions {from ground-based observations} and non thermal radio
emissions, from ground-based observations for Jupiter?s decametric radiation
and Cassini plasma wave measurements of the Saturn Kilometric Radiation
{SKR}.

WFPC2 10798

Dark Halos and Substructure from Arcs & Einstein Rings

The surface brightness distribution of extended gravitationally lensed arcs
and Einstein rings contains super-resolved information about the lensed
object, and, more excitingly, about the smooth and clumpy mass distribution
of the lens galaxies. The source and lens information can non-parametrically
be separated, resulting in a direct "gravitational image" of the inner
mass-distribution of cosmologically-distant galaxies {Koopmans 2005;
Koopmans et al. 2006 [astro-ph/0601628]}. With this goal in mind, we propose
deep HST ACS-F555W/F814W and NICMOS-F160W WFC imaging of 20 new
gravitational-lens systems with spatially resolved lensed sources, of the 35
new lens systems discovered by the Sloan Lens ACS Survey {Bolton et al.
2005} so far, 15 of which are being imaged in Cycle-14. Each system has been
selected from the SDSS and confirmed in two time- efficient HST-ACS snapshot
programs {cycle 13&14}. High-fidelity multi-color HST images are required
{not delivered by the 420s snapshots} to isolate these lensed images
{properly cleaned, dithered and extinction-corrected} from the lens galaxy
surface brightness distribution, and apply our "gravitational maging"
technique. Our sample of 35 early-type lens galaxies to date is by far the
largest, still growing, and most uniformly selected. This minimizes
selection biases and small-number statistics, compared to smaller, often
serendipitously discovered, samples. Moreover, using the WFC provides
information on the field around the lens, higher S/N and a better understood
PSF, compared with the HRC, and one retains high spatial resolution through
drizzling. The sample of galaxy mass distributions - determined through this
method from the arcs and Einstein ring HST images - will be studied to: {i}
measure the smooth mass distribution of the lens galaxies {dark and luminous
mass are separated using the HST images and the stellar M/L values derived
from a joint stellar-dynamical analysis of each system}; {ii} quantify
statistically and individually the incidence of mass-substructure {with or
without obvious luminous counter- parts such as dwarf galaxies}. Since
dark-matter substructure could be more prevalent at higher redshift, both
results provide a direct test of this prediction of the CDM hierarchical
structure-formation model.

WFPC2 10888

Complexity in the Smallest Galaxies: Star Formation History of the Sculptor
Dwarf Spheroidal

The Sculptor dwarf spheroidal galaxy {Scl dSph} is one of the most luminous
of the Milky Way dSph satellites, suffers virtually no foreground confusion
or reddening because of its high galactic latitude, and is nearby at 80 kpc
from the Sun. It is of great interest to astronomy to understand the
detailed histories of dSph galaxies because they may be survivors of the
hierarchical merging process that created giant galaxies like our own.
Despite this, the age distribution of stars in Scl dSph remains remarkably
poorly constrained because of a dearth of high-quality color-magnitude
diagrams {CMDs} of its central regions. Scl dSph is known to be complex on
the basis of shallower photometry, radial velocity studies, and
investigations of the metallicity; however, the age range of significant
star-formation and the proportion of stars older and younger than 10 Gyr is
still completely unknown. The age of the centrally concentrated, metal-rich
population has never been measured. We propose to obtain deep optical images
of the core of Scl dSph with WFPC2 in order to measure the temporal
evolution of its star-formation rate over its entire lifetime. The ONLY way
to reliably measure the variation in star-formation rate on Gyr timescales
at ages of 10-13 Gyr is with photometry of a large number of stars at and
below the oldest main-sequence turnoffs to magnitudes of {B,I} = {25.1,
24.5}. Because of the high stellar density and resulting image crowding, it
is impossible to achieve the required level of photometric precision except
with diffraction-limited imaging. These data will permit the first reliable
measurement of the star-formation history of the main body of Scl dSph;
limited inferences from WFPC2 data in an outer field have been made, but
they were hindered not only by small number statistics but by the subsequent
revelation of extremely strong population gradients in Scl dSph, such that
the stars in the existing WFPC2 field are not representative of the galaxy
as a whole. Our proposed program will shed strong new light on the formation
processes of the smallest galaxies. Only by measuring the detailed early
histories of galaxies like Scl dSph can we evaluate the impact of outside
influences like ram-pressure stripping, tidal stirring, and photoionization
feedback on the evolution of small galaxies.

WFPC2 10903

Resolving the LMC Microlensing Puzzle: Where are the Lensing Objects?

We are requesting 12 HST orbits to continue to investigate the nature of the
population that gives rise to the microlensing seen towards the LMC. This
proposal builds on the cycle 14 HST program {10583} and will complement the
study with 12 yet-to-be discovered microlensing candidates from Fall 2006.
Our SuperMacho project is an ongoing ground- based survey on the CTIO 4m
that has demonstrated the ability to detect LMC microlensing events via
frame subtraction. The combination of high angular resolution and
photometric accuracy with HST will allow us to 1} confrim that the detected
flux excursions arise from LMC stars, rather than background supernovae or
AGN, and 2} obtain reliable baseline flux measurements for the objects in
their unlensed state. This latter measurement in important in determining
the microlensing optical depth towards the LMC.

FLIGHT OPERATIONS SUMMARY:

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

HSTARS:

10811 - REACQ(1,2,1) failed, Search Radius Limit Exceeded on FGS 1

Upon acquisition of signal at 136/00:53:48, vehicle was in gyro control with
FGS 1 search radius limit flag set. REACQ(1,2,1) at 135/23:32:53 failed with
search radius limit exceeded on FGS 1. OBAD map after GSACQ failure showed
RSS error of 45.81 arcseconds.

COMPLETED OPS REQUEST: (None)

COMPLETED OPS NOTES: (None)

SCHEDULED SUCCESSFUL

FGS GSacq 06 06
FGS REacq 04 03
OBAD with Maneuver 20 20

SIGNIFICANT EVENTS: (None)
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