Daily Report # 4325

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 # 4325

PERIOD COVERED: UT March 22, 2007 (DOY 081)

OBSERVATIONS SCHEDULED

ACS/SBC 10814

The Masses for ultraluminous X-ray sources

Ultraluminous X-ray sources are non-nuclear sources in normal disk
galaxies that are either stellar mass black holes that are
super-Eddington emitters, or 1E3-1E4 Msolar black holes emitting
normally. We can distinguish between these models by obtaining
constraints for the mass of the primary, which can be accomplished
through UV objective prism spectra. This strategy begins with the
optical identification of the secondary and identification of its
spectral type in order to determine its mass and the Roche Lobe
radius. Secondly, we need to determine whether an accretion disk is
present and if its high ionization UV line luminosities point to a
stellar mass black hole or a more massive object. Finally, if the
black hole is 1E3-1E4 Msolar, the orbital velocity of the secondary is
so large that a Doppler shift will be detectable, even at the modest
resolution of the prism.

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 10815

The Blue Hook Populations of Massive Globular Clusters

Blue hook stars are a class of hot {~35,000 K} subluminous horizontal
branch stars that have been recently discovered using HST ultraviolet
images of the globular clusters omega Cen and NGC 2808. These stars
occupy a region of the HR diagram that is unexplained by canonical
stellar evolution theory. Using new theoretical evolutionary and
atmospheric models, we have shown that the blue hook stars are very
likely the progeny of stars that undergo extensive internal mixing
during a late helium core flash on the white dwarf cooling curve. This
"flash mixing" produces an enormous enhancement of the surface helium
and carbon abundances, which suppresses the flux in the far
ultraviolet. Although flash mixing is more likely to occur in stars
that are born with high helium abundances, a high helium abundance, by
itself, does not explain the presence of a blue hook population -
flash mixing of the envelope is required. We propose ACS ultraviolet
{SBC/F150LP and HRC/F250W} observations of the five additional
globular clusters for which the presence of blue hook stars is
suspected from longer wavelength observations. Like omega Cen and NGC
2808, these five targets are also among the most massive globular
clusters, because less massive clusters show no evidence for blue hook
stars. Because our targets span 1.5 dex in metallicity, we will be
able to test our prediction that flash-mixing should be less drastic
in metal-rich blue hook stars. In addition, our observations will test
the hypothesis that blue hook stars only form in globular clusters
massive enough to retain the helium- enriched ejecta from the first
stellar generation. If this hypothesis is correct, then our
observations will yield important constraints on the chemical
evolution and early formation history in globular clusters, as well as
the role of helium self-enrichment in producing blue horizontal branch
morphologies and multiple main sequence turnoffs. Finally, our
observations will provide new insight into the formation of the
hottest horizontal branch stars, with implications for the origin of
the hot helium-rich subdwarfs in the Galactic field.

NIC1/NIC2/NIC3 8795

NICMOS Post-SAA calibration - CR Persistence Part 6

A new proceedure proposed to alleviate the CR-persistence problem of
NICMOS. Dark frames will be obtained immediately upon exiting the SAA
contour 23, and everytime 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 i mages. Each observation will need its
own CRMAP, as different SAA passages leave different imprints on the
NICMOS detectors.

NIC3 11080

Exploring the Scaling Laws of Star Formation

As a variety of surveys of the local and distant Universe are
approaching a full census of galaxy populations, our attention needs
to turn towards understanding and quantifying the physical mechanisms
that trigger and regulate the large-scale star formation rates {SFRs}
in galaxies.

FLIGHT OPERATIONS SUMMARY:

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

HSTARS: (None)

COMPLETED OPS REQUEST: (None)

COMPLETED OPS NOTES: (None)

SCHEDULED SUCCESSFUL

FGS GSacq 06 06
FGS REacq 08 08
OBAD with Maneuver 28 28

SIGNIFICANT EVENTS: (None)