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Daily Report #4499



 
 
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Old December 4th 07, 06:38 PM posted to sci.astro.hubble
Cooper, Joe
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Default Daily Report #4499

HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT***** # 4499

PERIOD COVERED: UT December 4, 2007 (DOY 338)

OBSERVATIONS SCHEDULED

ACS/SBC 10907

New Sightlines for the Study of Intergalactic Helium: A Dozen
High-Confidence, UV-Bright Quasars from SDSS/GALEX

The reionization of intergalactic helium is thought to have occurred
between redshifts of about 3 and 4. Detailed study of HeII Lyman-alpha
absorption toward a handful quasars at 2.7z3.3 demonstrates the
great potential of such probes of the IGM, but the current
critically-small sample limits confidence in resulting cosmological
inferences. The requisite unobscured quasar sightlines to
high-redshift are extremely rare, especially due to severe absorption
in random intervening Lyman-limit systems, but SDSS provides thousands
of z3.1 quasars potentially suitable for HeII studies. We have
cross-correlated SDSS quasars with GALEX UV sources to obtain a dozen
new, very high-confidence, candidate quasars/sightlines {z=3.1 to 4.1}
potentially useful for detailed HeII studies even with current HST
instruments. We propose brief, 2-orbit per target, reconnaissance
spectral exposures with the ACS SBC prism to definitively verify UV
flux down to the HeII break. Our combined SDSS/GALEX selection insures
a very high-yield of confirmations, as the quasars are already known
to be UV-bright from broadband GALEX images. The additional
sightlines, extending to very high-redshift, will directly enable
ensemble spectral stacks, as well as long exposure follow-up spectra,
at high S/N with the ACS/SBC ultraviolet prisms {or perhaps STIS or
COS later}, to confidently measure the spectrum and evolution of the
ionizing background radiation, the evolution of HeII opacity, and the
density of intergalactic baryons.

WFPC2 10829

Secular Evolution at the End of the Hubble Sequence

The bulgeless disk galaxies at the end of the Hubble Sequence evolve
at a glacial pace relative to their more violent, earlier-type
cousins. The causes of their internal, or secular evolution are
important because secular evolution represents the future fate of all
galaxies in our accelerating Universe and is a key ingredient to
understanding galaxy evolution in lower-density environments at
present. The rate of secular evolution is largely determined by the
stability of the cold ISM against collapse, star formation, and the
buildup of a central bulge. Key diagnostics of the ISM's stability are
the presence of compact molecular clouds and narrow dust lanes.
Surprisingly, edge-on, pure disk galaxies with circular velocities
below 120 km/s do not appear to contain such dust lanes. We propose to
obtain ACS/WFC F606W images of a well-selected sample of extremely
late-type disk galaxies to measure the characteristic scale size of
the cold ISM and determine if they possess the unstable, cold ISM
necessary to drive secular evolution. Our sample has been carefully
constructed to include disk galaxies above and below the critical
circular velocity of 120 km/s where the dust properties of edge-on
disks change so remarkably. We will then use surface brightness
profiles to search for nuclear star clusters and pseudobulges, which
are early indicators that secular evolution is at work, as well as
measure the pitch angle of the dust lanes as a function of radius to
estimate the central mass concentrations.

WFPC2 11024

WFPC2 CYCLE 15 INTERNAL MONITOR

This calibration proposal is the Cycle 15 routine internal monitor for
WFPC2, to be run weekly to monitor the health of the cameras. A
variety of internal exposures are obtained in order to provide a
monitor of the integrity of the CCD camera electronics in both bays
{both gain 7 and gain 15 -- to test stability of gains and bias
levels}, a test for quantum efficiency in the CCDs, and a monitor for
possible buildup of contaminants on the CCD windows. These also
provide raw data for generating annual super-bias reference files for
the calibration pipeline.

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 DARKs. 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 11197

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 that 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 Phillip's relation over
cosmic time. High signal-to-noise measurements of 16 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. In Cycle 15 we obtained
NICMOS photometry of 8 ESSENCE supernovae and are awaiting template
observations to place them on the IR Hubble diagram. Here we request
another 8 supernovae be studied in the final season of the ESSENCE
search. 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.

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.

WFPC2 11029

WFPC2 CYCLE 15 Intflat Linearity Check and Filter Rotation Anomaly
Monitor

Intflat observations will be taken to provide a linearity check: the
linearity test consists of a series of intflats in F555W, in each gain
and each shutter. A combination of intflats, visflats, and earthflats
will be used to check the repeatability of filter wheel motions.
{Intflat sequences tied to decons, visits 1-18 in prop 10363, have
been moved to the cycle 15 decon proposal xxxx for easier scheduling.}
Note: long-exposure WFPC2 intflats must be scheduled during ACS
anneals to prevent stray light from the WFPC2 lamps from contaminating
long ACS external exposures.

WFPC2 11032

CTE Extended Targets Closeout

Measuring the charge transfer efficiency {CTE} of an astronomical CCD
camera is crucial to determining the CCD's photometric fidelity across
the field of view. WFPC2's CTE has degraded steadily over the last 13
years because of continuous exposure to trapped particles in HST's
radiation environment. The fraction of photometric signal lost from
WFPC2's CTI {change transfer inefficiency} is a function of WFPC2's
time in orbit, the integrated signal in the image, the location of the
image on the CCD, and the background signal. Routine monitoring of
WFPC2's degrading CTE over the last 13 years has primarily concerned
the effects of CTI on point-source photometry. However, most of the
sources imaged by WFPC2 are extended rather than point-like. This
program aims to characterize the effects of CTI on the photometry and
morphology of extended sources near the end of WFPC2's functional
life. Images of a standard field within the rich galaxy cluster Abell
1689 are recorded with each WFPC2 camera using the F606W and F814W
filters. These images will be compared with contemporaneous images of
Abell 1689 recorded with the field rotated by approximately 180
degrees to assess differences between extended sources imaged near and
far from the serial register. The images will also be compared with
similar images recorded in Cycle 8 {Program 8456} to characterize the
rate of CTE degradation over the lifetime of WFPC2.

WFPC2 11070

WFPC2 CYCLE 15 Standard Darks - part II

This dark calibration program obtains dark frames every week in order
to provide data for the ongoing calibration of the CCD dark current
rate, and to monitor and characterize the evolution of hot pixels.
Over an extended period these data will also provide a monitor of
radiation damage to the CCDs.

WFPC2 11103

A Snapshot Survey of The Most Massive Clusters of Galaxies

We propose the continuation of our highly successful SNAPshot survey
of a sample of 125 very X-ray luminous clusters in the redshift range
0.3-0.7. As demonstrated by the 25 snapshots obtained so far in
Cycle14 and Cycle15 these systems frequently exhibit strong
gravitational lensing as well as spectacular examples of violent
galaxy interactions. The proposed observations will provide important
constraints on the cluster mass distributions, the physical nature of
galaxy-galaxy and galaxy-gas interactions in cluster cores, and a set
of optically bright, lensed galaxies for further 8-10m spectroscopy.
All of our primary science goals require only the detection and
characterization of high-surface-brightness features and are thus
achievable even at the reduced sensitivity of WFPC2. Because of their
high redshift and thus compact angular scale our target clusters are
less adversely affected by the smaller field of view of WFPC2 than
more nearby systems. Acknowledging the broad community interest in
this sample we waive our data rights for these observations. Due to a
clerical error at STScI our approved Cycle15 SNAP program was barred
from execution for 3 months and only 6 observations have been
performed to date - reinstating this SNAP at Cycle16 priority is of
paramount importance to reach meaningful statistics.

WFPC2 11134

WFPC2 Tidal Tail Survey: Probing Star Cluster Formation on the Edge

The spectacular HST images of the interiors of merging galaxies such
as the Antennae and NGC 7252 have revealed rich and diverse
populations of star clusters created over the course of the
interaction. Intriguingly, our WFPC2 study of tidal tails in these and
other interacting pairs has shown that star cluster birth in the tails
does not follow a similarly straightforward evolution. In fact,
cluster formation in these relatively sparse environments is not
guaranteed -- only one of six tails in our initial study showed
evidence for a significant population of young star clusters. The tail
environment thus offers the opportunity to probe star cluster
formation on the edge of the physical parameter space {e.g., of
stellar and gas mass, density, and pressure} that permits it to occur.
We propose to significantly extend our pilot sample of optically
bright, gas-rich tidal tails by a factor of 4 in number to include a
more diverse population of tails, encompassing major and minor
mergers, gas-rich and gas-poor tails, as well as early, late, and
merged interaction stages. With 21 orbits of HST WFPC2 imaging in the
F606W and F814W filters, we can identify, roughly age-date, and
measure sizes of star clusters to determine what physical parameters
affect star cluster formation. WFPC2 imaging has been used effectively
in our initial study of four mergers, and it will be possible in this
program to reach similar limits of Mv=-8.5 for each of 16 more tails.
With the much larger sample we expect to isolate which factors, such
as merger stage, HI content, and merger mass ratio, drive the
formation of star clusters.

WFPC2 11361

Hubble Heritage Observations of Mars at 2007 Opposition

We will obtain images of Mars at opposition in December 2007.

FLIGHT OPERATIONS SUMMARY:

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

HSTARS:

11086 - GSaq(2,3,3) failed to RGA hold

At AOS 338/04:32:30 flags indicated that during LOS GSacq(2,3,3)
scheduled at 338/04:00:52 failed to RGA hold due to receiving stop
flag QF2STOPF on FGS 2.

COMPLETED OPS REQUEST: (None)

COMPLETED OPS NOTES: (None)

*********************** SCHEDULED***** SUCCESSFUL

FGS GSacq************** 08**************** 07
FGS REacq************** 06***************** 06
OBAD with Maneuver **** 28***************** 28

SIGNIFICANT EVENTS: (None)


 




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