Notice: Due to the conversion of some ACS WFC or HRC observations into

WFPC2, or NICMOS observations after the loss of ACS CCD science

capability in January, there may be an occasional discrepancy between a

proposal's listed (and correct) instrument usage and the abstract that

follows it.

 

HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

 

DAILY REPORT    # 4425

 

PERIOD COVERED: UT August 13, 2007 (DOY 225)

 

OBSERVATIONS SCHEDULED

 

ACS/SBC WFPC2 11175

 

UV Imaging to Determine the Location of Residual Star Formation in

Galaxies Recently Arrived on the Red Sequence

 

We have identified a sample of low-redshift {z = 0.04 - 0.10} galaxies

that are candidates for recent arrival on the red sequence. They have

red optical colors indicative of old stellar populations, but blue

UV-optical colors that could indicate the presence of a small quantity

of continuing or very recent star formation. However, their spectra lack

the emission lines that characterize star-forming galaxies. We propose

to use ACS/SBC to obtain high- resolution imaging of the UV flux in

these galaxies, in order to determine the spatial distribution of the

last episode of star formation. WFPC2 imaging will provide B, V, and I

photometry to measure the main stellar light distribution of the galaxy

for comparison with the UV imaging, as well as to measure color

gradients and the distribution of interstellar dust. This detailed

morphological information will allow us to investigate the hypothesis

that these galaxies have recently stopped forming stars and to compare

the observed distribution of the last star formation with predictions

for several different mechanisms that may quench star formation in

galaxies.

 

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.

 

WFPC2 11133

 

Late-Time Photometry of SN 2005hk: A New Kind of Type Ia Supernova

 

Our lack of understanding of Type Ia supernova {SN Ia} explosions limits

our confidence in their use for cosmology. While there is broad

agreement that these objects represent the explosions of white dwarfs,

the details of the explosion mechanism are not well- understood. Recent

observations have detected a previously unacknowledged variant class of

SNe Ia whose photometric and spectroscopic peculiarities make them quite

distinct from normal SNe Ia. These objects represent a challenge for

thermonuclear supernova models, as a complete theory of exploding white

dwarfs must allow for their existence. A particularly well-studied

example of this class of objects is the recent SN 2005hk, whose

properties in some respects resemble those of models which invoke a

subsonic burning front, called a deflagration. We propose to test SN Ia

models by obtaining late-time photometry for this extreme SN Ia using

WFPC2 and NICMOS on HST. We will accurately measure the late-time

photometric decline rate and spectral energy distribution {SED}. These

observations will allow us to test whether the ejecta contain the large

amount of oxygen predicted by certain models, the efficiency of energy

deposition by gamma rays and positrons, and possibly detect major

evolution of the SED expected due to a change in the dominant cooling

mechanism of the ejecta.

 

WFPC2 11023

 

WFPC2 CYCLE 15 Standard Darks - part 1

 

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 11169

 

Collisions in the Kuiper belt

 

For most of the 15 year history of observations of Kuiper belt objects,

it has been speculated that impacts must have played a major role in

shaping the physical and chemical characteristics of these objects, yet

little direct evidence of the effects of such impacts has been seen. The

past 18 months, however, have seen an explosion of major new discoveries

giving some of the first insights into the influence of this critical

process. From a diversity of observations we have been led to the

hypotheses that: {1} satellite- forming impacts must have been common in

the Kuiper belt; {2} such impacts led to significant chemical

modification; and {3} the outcomes of these impacts are sufficiently

predictable that we can now find and study these impact-derived systems

by the chemical and physical attributes of both the satellites and the

primaries. If our picture is correct, we now have in hand for the first

time a set of incredibly powerful tools to study the frequency and

outcome of collisions in the outer solar system. Here we propose three

linked projects that would answer questions critical to the multiple

prongs of our hypothesis. In these projects we will study the chemical

effects of collisions through spectrophotometric observations of

collisionally formed satellites and through the search for additional

satellites around primaries with potential impact signatures, and we

will study the physical effects of impacts through the examination of

tidal evolution in proposed impact systems. The intensive HST program

that we propose here will allow us to fully test our new hypotheses and

will provide the ability to obtain the first extensive insights into

outer solar system impact processes.

 

WFPC2 11176

 

Location and the Origin of Short Gamma-Ray Bursts

 

During the past decade extraordinary progress has been made in

determining the origin of long-duration gamma-ray bursts. It has been

conclusively shown that these objects derive from the deaths of massive

stars. Nonetheless, the origin of their observational cousins,

short-duration gamma-ray bursts {SGRBs} remains a mystery. While SGRBs

are widely thought to result from the inspiral of compact binaries, this

is a conjecture. A number of hosts of SGRBs have been identified, and

have been used by some to argue that SGRBs derive primarily from an

ancient population {~ 5 Gyr}; however, it is not known whether this

conclusion more accurately reflects selection biases or astrophysics.

Here we propose to employ a variant of a technique that we pioneered and

used to great effect in elucidating the origins of long-duration bursts.

We will examine the degree to which SGRB locations trace the red or blue

light of their hosts, and thus old or young stellar populations. This

approach will allow us to study the demographics of the SGRB population

in a manner largely free of the distance dependent selection effects

which have so far bedeviled this field, and should give direct insight

into the age of the SGRB progenitor population.

 

WFPC2 11178

 

Probing Solar System History with Orbits, Masses, and Colors of

Transneptunian Binaries

 

The recent discovery of numerous transneptunian binaries {TNBs} opens a

window into dynamical conditions in the protoplanetary disk where they

formed as well as the history of subsequent events which sculpted the

outer Solar System and emplaced them onto their present day heliocentric

orbits. To date, at least 47 TNBs have been discovered, but only about a

dozen have had their mutual orbits and separate colors determined,

frustrating their use to investigate numerous important scientific

questions. The current shortage of data especially cripples scientific

investigations requiring statistical comparisons among the ensemble

characteristics. We propose to obtain sufficient astrometry and

photometry of 23 TNBs to compute their mutual orbits and system masses

and to determine separate primary and secondary colors, roughly tripling

the sample for which this information is known, as well as extending it

to include systems of two near-equal size bodies. To make the most

efficient possible use of HST, we will use a Monte Carlo technique to

optimally schedule our observations.

 

WFPC2 11292

 

The Ring Plane Crossings of Uranus in 2007

 

The rings of Uranus turn edge-on to Earth in May and August 2007. In

between, we will have a rare opportunity to see the unlit face of the

rings. With the nine optically thick rings essentially invisible, we

will observe features and phenomena that are normally lost in their

glare. We will use this opportunity to search thoroughly for the

embedded "shepherd" moons long believed to confine the edges of the

rings, setting a mass limit roughly 10 times smaller than that of the

smallest shepherd currently known, Cordelia. We will measure the

vertical thicknesses of the rings and study the faint dust belts only

known to exist from a single Voyager image. We will also study the

colors of the newly-discovered faint, outer rings; recent evidence

suggests that one ring is red and the other blue, implying that each

ring is dominated by a different set of physical processes. We will

employ near- edge-on photometry from 2006 and 2007 to derive the

particle filling factor within the rings, to observe how ring epsilon

responds to the "traffic jam" as particles pass through its narrowest

point, and to test the latest models for preserving eccentricities and

apse alignment within the rings. Moreover, this data set will allow us

to continue monitoring the motions of the inner moons, which have been

found to show possibly chaotic orbital variations; by nearly doubling

the time span of the existing Hubble astrometry, the details of the

variations will become much clearer.

 

WFPC2 11312

 

The Local Cluster Substructure Survey {LoCuSS}: Deep Strong Lensing

Observations with WFPC2

 

LoCuSS is a systematic and detailed investigation of the mass,

substructure, and thermodynamics of 100 X-ray luminous galaxy clusters

at 0.15<z<0.3. The primary goal is to test our recent suggestion that

this population is dominated by dynamically immature disturbed clusters,

and that the observed mass-temperature relation suffers strong

structural segregation. If confirmed, this would represent a paradigm

shift in our observational understanding of clusters, that were hitherto

believed to be dominated by mature, undisturbed systems. We propose to

complete our successful Cycle 15 program {SNAP:10881} which prior to

premature termination had delivered robust weak-lensing detections in 17

clusters, and candidate strongly-lensed arcs in 11 of these 17. These

strong and weak lensing signals will give an accurate measure of the

total mass and structure of the dark matter distribution that we will

subsequently compare with X-ray and Sunyaev Zeldovich Effect

observables. The broader applications of our project include 1} the

calibration of mass-temperature and mass-SZE scaling relations which

will be critical for the calibration of proposed dark energy

experiments, and 2} the low redshift baseline study of the demographics

of massive clusters to aid interpretation of future high redshift {z>1}

cluster samples. To complete the all-important high resolution imaging

component of our survey, we request deep WFPC2 observations of 20

clusters through the F606W filter, for which wide-field weak-lensing

data are already available from our Subaru imaging program. The

combination of deep WFPC2 and Subaru data for these 20 clusters will

enable us to achieve the science program approved by the Cycle 15 TAC.

 

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)

 

                      SCHEDULED      SUCCESSFUL   

FGS GSacq               07                07                        

FGS REacq               08                08               

OBAD with Maneuver 30                30              

 

COMPLETED OPS NOTES: (None)