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Daily Report #4392



 
 
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Old June 27th 07, 07:34 PM posted to sci.astro.hubble
Bassford, Lynn
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Posts: 44
Default Daily Report #4392

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 # 4392

PERIOD COVERED: UT June 26, 2007 (DOY 177)

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.

ACS/SBC 10872

Lyman Continuum Emission in Galaxies at z=1.2

Lyman continuum photons produced in massive starbursts may have played a
dominant role in the reionization of the Universe. Starbursts are important
contributors to the ionizing metagalactic background at lower redshifts as
well. However, their contribution to the background depends upon the
fraction of ionizing radiation that escapes from the intrinsic opacity of
galaxies below the Lyman limit. Current surveys suggest escape fractions of
a few percent, up to 10%, with very few detections {as opposed to upper
limits} having been reported. No detections have been reported in the epochs
between z=0.1 and z=2. We propose to measure the fraction of escaping Lyman
continuum radiation from 15 luminous z~1.2 galaxies in the GOODS fields.
Using the tremendous sensitivity of the ACS Solar- blind Channel, we will
reach AB=30 mag., allowing us to detect an escape fraction of 1%. We will
correlate the amount of escaping radiation with the photometric and
morphological properties of the galaxies. A non-detection in all sources
would imply that QSOs provide the overwhelming majority of ionizing
radiation at z=1.3, and it would strongly indicate that the properties of
galaxies at higher redshift have to be significantly different for galaxies
to dominate reionization. The deep FUV images will also be useful for
extending the FUV study of other galaxies in the GOODS fields.

NIC1/NIC2/NIC3 8794

NICMOS Post-SAA calibration - CR Persistence Part 5

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 10893

Sweeping Away the Dust: Reliable Dark Energy with an Infrared Hubble Diagram

We propose building a high-z Hubble Diagram using type Ia supernovae
observed in the infrared rest-frame J-band. The infrared has a number of
exceptional properties. The effect of dust extinction is minimal, reducing a
major systematic tha may be biasing dark energy measurements. Also, recent
work indicates that type Ia supernovae are true standard candles in the
infrared meaning that our Hubble diagram will be resistant to possible
evolution in the Phillips relation over cosmic time. High signal-to-noise
measurements of 9 type Ia events at z~0.4 will be compared with an
independent optical Hubble diagram from the ESSENCE project to test for a
shift in the derived dark energy equation of state due to a systematic bias.
Because of the bright sky background, H-band photometry of z~0.4 supernovae
is not feasible from the ground. Only the superb image quality and dark
infrared sky seen by HST makes this test possible. This experiment may also
lead to a better, more reliable way of mapping the expansion history of the
universe with the Joint Dark Energy Mission.

WFPC2 10834

The Shell of the Recurrent Nova T Pyx

T Pyx is the only known recurrent nova with a shell. This 'shell' is
mysterious because it has been resolved into thousands of knots that
apparently aren't expanding. We propose to take a deep F658N image of T Pyx
during one orbit to serve as a 12 year baseline from the previous HST WFPC2
images in 1994 and 1995. This much longer baseline will allow us to push
down the limits on expansion velocities to ~10 km/s and will allow us to
measure the lifetimes of the knots. Also, we expect to discover the
expanding inner shell from the last eruption in 1966 which should now have
expanded to ~0.9" in radius. Detailed modeling of the observed line fluxes
will give the mass of the individual knots and the shells. The details of
the expansion velocities, lifetimes, and masses of the knots will determine
the nature of the T Pyx shell; with alternatives being a nova shell, a
planetary nebula, stalled shocks in a pre-existing shell, or a cloud ionized
by the high luminosity and temperature of the white dwarf. If we can
separate out the mass ejected during the 1966 eruption, then we can compare
it to the total mass accreted between the 1944 and 1966 eruptions {6.0x10^-6
solar mass} so as to determine whether the white dwarf is gaining or losing
mass on average. If the white dwarf is gaining mass, then it must inevitably
exceed the Chandrasekhar mass and collapse as a Type Ia supernova, and thus
recurrent novae would be shown to be an important component of the solution
to the Type Ia progenitor problem.

WFPC2 11112

The Collisional Ring Galaxy NGC922

We request WFPC2 images of the newly recognized collisional ring galaxy
NGC922 which will become the nearest such system observed by HST. These will
be used to get a clear understanding of the geometry of the interaction and
the induced star formation in this system. Quantitive modeling of the colors
of the star clusters and stellar populations will be used to constrain the
star formation history of the system. They will also be used to test the
"infant mortality" scenario for star cluster evolution. The derived
population ages will test predictions of how star formation evolves in the
various components {ring, core, spokes} of collisional rings, and will
improve our own simulations of this system. These will be used to determine
the final fate of the stars formed in the present burst - some will end up
in a central bar or bulge while others will become part of a thickened disk.
By analogy this will tell us how similar collisions enrich stellar
populations in the early universe. This is especially relevant since the
number density of collisional rings increases rapidly with redshift.

WFPC2 11140

Can mass-ejections from late He-shell flash stars constrain
convective/reactive flow modeling of stellar interiors?

The existence of H-deficient knots around the central stars of the planetary
nebulae Abell 30 and Abell 78 is still unexplained. We hypothesize that
these knots were ejected during a very late helium-shell flash {= very late
thermal pulse, VLTP} suffered by the precursor white dwarf stars. If this is
true, then the characteristics of these knots {mass, velocity, density,
spatial distribution} allow to draw conclusions on the course of the
hydrogen- ingestion flash detonation that is triggered by the He-shell
flash. This provides important, otherwise inaccessible constraints for the
hydrodynamical modeling of convective/reactive flows in stellar interiors.
Understanding the physics of these flows is not only important for the
understanding of these particular central stars, but also for the frequent,
very similar convective/reactive events that determine the nucleosynthesis
in Pop. III stars. With this proposal we want to proof or discard the idea
that the H-deficient knots are resulting from a VLTP. If true, then they can
be exploited for flash-physics diagnostics. We propose a simple test. We
search for such knots around five H-deficient central stars {PG1159 stars}.
Our models predict, that only those stars with residual nitrogen in the
atmosphere have suffered a VLTP and, hence, should have expelled knots. We
therefore want to take [O III] images of stars which have photospheric N and
those which do not.

FLIGHT OPERATIONS SUMMARY:

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

HSTARS:

10871 - OBAD Failed Identification

OBAD2 scheduled at 177/09:42:35 failed. Status Buffer message 1902 "OBAD
Failed Identification" was received. GSacq was successful. OBAD1 RSS error
was 10957.43 arcseconds

COMPLETED OPS REQUEST:

18111-0 - Modify Magnitude Threshold Values in SOB Macros


COMPLETED OPS NOTES: (None)

SCHEDULED SUCCESSFUL
FGS GSacq 04 04
FGS REacq 09 09
OBAD with Maneuver 24 23

SIGNIFICANT EVENTS:

Flash Report: FHST Stuck-on-Bottom (SOB) Macro Visual-Magnitude Threshold
Modification: Operations Request 18111-0 to modify the magnitude threshold
values in the SOB macros to a magnitude value of 3 was completed at
177/14:39:24.

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