Status Report

NASA Hubble Space Telescope Daily Report # 3682

By SpaceRef Editor
August 27, 2004
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HUBBLE SPACE TELESCOPE – Continuing to collect World Class Science





CCD Daily Monitor

This program consists of basic tests to monitor, the read noise, the
development of hot pixels and test for any source of noise in ACS CCD
detectors. This programme will be executed once a day for the entire
lifetime of ACS.

ACS/WFC 10118

Imaging the Chemical Distribution in Type Ia SN Ejecta

We know Type Ia supernovae are thermonuclear explosions of CO white
dwarfs, but we don’t know the specifics of how the nuclear burning
process proceeds from the core outward once it starts. The
thermonuclear instability is thought to start off as a subsonic,
turbulent deflagration or burning wave but then, at some point, may
transition into a blast or detonation wave. In such "delayed
detonation" models, differences between normal and subluminous Type Ia
SNe reflect differences in the amount of burning that has occurred in
the pre-detonation phase. More burning helps to pre-expand the WD
before passage of the detontation wave, which then results in
different final element abundances and internal Fe-rich ejecta
structure. Directly imaging the 2-D chemical distribution of ejecta
from a Type Ia SN is actually possible in the case of the subluminous
Type Ia SN 1885, which occurred on the near-side of M31’s central
bulge. This 119 year old remnant is visible — from its core to its
outer edge — via strong optical/UV Ca and Fe line absorptions.
Remarkably, the SNR appears to still be in a nearly free expansion
phase, meaning that the elemental stratification seen present today
accurately reflects SN Ia explosive nucleosynthesis physics. We
propose to obtain ACS WFC/HRC images of SN 1885 in order to take
advantage of this extraordinary situation: Having a young, nearby Type
Ia SN remnant visible in silhouette against a galaxy-size light table.
These unique observations will reveal a SN Ia’s Ca and Fe ejecta
distribution, density structure, sphericity, and ionization state as a
function of expansion velocity, thereby confronting various SN Ia
models with detailed ejecta stratification and expansion velocity

ACS/WFC 10158

ACS Observations of the Gravitational Lens B1608+656: Characterizing
the Einstein Ring

We request time to obtain ACS deep images of the B1608+656
gravitational lens system to fully characterize its enclosing Einstein
ring with high signal-to-noise ratio {SNR}. These data will allow us
to determine the gravitational potential of the lens, locally, to
several percent accuracy and, combined with the three independent time
delays, measure H_0 to much better than 10% precision. For this goal,
we have developed powerful new lens modeling codes that make use of
the full brightness distribution of the Einstein ring in lens systems.
The B1608+656 system is ideal for our new code. It has precisely
measured time delays, a well-determined stellar velocity dispersion,
and an Einstein ring that is not dominated by the lensed nuclear
emission of the background source. When combined with high-SNR images
of Einstein rings, the new modeling codes provide qualitatively
different and much improved analysis of the ring emission than was
previously possible. The proposed ACS observations will reach the SNR
at which the new modeling code can be fully exploited {SNR=5 per
pixel}. Our simulations show that these new data will allow us to
reduce the total uncertainties in H_0 derived from the system by at
least a factor of two, to the 5-7% level for this system.

ACS/WFC 10178

Imaging Polarimetry of Young Stellar Objects with ACS and NICMOS: A
study in dust grain evolution

The formation of planetary systems is intimately linked to the dust
population in circumstellar disks, thus understanding dust grain
evolution is essential to advancing our understanding of how planets
form. By combining {1} the high resolution polarimetric capabilities
of ACS and NICMOS, {2} powerful 3-D radiative transfer codes, and {3}
observations of objects known to span the earliest stellar
evolutionary phases, we will gain crucial insight into the initial
phases of dust grain growth: evolution away from an ISM distribution.
Fractional polarization is a strong function of wavelength, therefore
by comparing polarimetric images in the optical and infrared, we can
sensitively constrain not only the geometry and optical depth of the
scattering medium, but also the grain size distribution. By observing
objects representative of the earliest evolutionary sequence of YSOs,
we will be able to investigate how the dust population evolves in size
and distribution during the crucial transition from a disk+envelope
system to a disk+star system. The proposed study will help to
establish the fundamental time scales for the initial depletion of
ISM-like grains: the first step in understanding the transformation
from small submicron sized dust grains, to large millimeter sized
grains, and untimely to planetary bodies.

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.

WFPC2 10071

WFPC2 CYCLE 12 Supplemental Darks Part 3/3

This dark calibration program obtains 3 dark frames every day to
provide data for monitoring and characterizing the evolution of hot

WFPC2 10080

Wavelength Stability of Narrow Band and Linear Ramp Filters

Verify the mapping of wavelength as a function of CCD position on
LRFs; check for changes in central wavelengths of narrow band filters.


Significant Spacecraft Anomalies: (The following are preliminary
reports of potential non-nominal performance that will be
investigated.) None



1263-0 Dump Table 212 @ 238/1130z

1264-0 Full HST486 RAM Memory Dump @ 238/1542z

                         SCHEDULED     SUCCESSFUL    FAILURE TIMES
FGS GSacq              07                       07
FGS REacq              08                       08
FHST Update            10                       10


Battery 3 Capacity Test continues. After approximately 52 hours of
discharge, the target low Voltage was reached and the reconditioning
resistor was autonomously turned off by HST486 FSW during a data
outage occurring 238/16:23Z – 16:46Z. EPS hardware reconfiguration was
completed during the third orbit night following discharge
termination, with the reconnection of Solar Array Section 3 to Battery
3 occurring @ 238/21:03Z. Trickle Charge was achieved in approximately
46 minutes during the first orbit day pass following the configuration
back to a hardware 6-battery system. Enabling OCA scheduled for
239/11:10Z, placing Battery 3 in FSW 6-battery system scheduled
239/17:40Z. Continuous ESTR Engineering coverage continues during
Battery 3 Capacity Testing.

SpaceRef staff editor.