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      # 4449

PERIOD COVERED: UT September 17, 2007 (DOY 260)

OBSERVATIONS SCHEDULED

WFPC2 10789

The Role of Environment in the Formation of Dwarf Galaxies

Clusters of galaxies contain an overdensity of dwarfs compared to the

field. Within galaxy clusters there is also a correlation between the

overdensity of dwarfs and local galaxy density, such that areas of lower

galaxy density contain more dwarfs per giant. The origin of these

'extra' dwarfs is unknown, but a large fraction of them did not form

through standard collapses early in the universe. Some dwarf ellipticals

in clusters have metal rich and young {< 6 Gyr} stellar populations

while others contain old metal poor populations, suggesting multiple

formation mechanisms and time scales. We propose to test the idea that

dwarfs descend from galaxies accreted into clusters during the past 8

Gyr by correlating ages and metallicities of dwarfs with their internal

structures - spiral arms, bars, and disks. If dwarfs originate from more

massive galaxies then these features should be common in metal rich and

young dwarfs. On the other hand, if no correlation is found it would

suggest that dwarfs form through in-situ collapses of gas in the

intragalactic medium after the universe was reionized.

WFPC2 11027

Visible Earth Flats

This proposal monitors flatfield stability. This proposal obtains

sequences of Earth streak flats to construct high quality flat fields

for the WFPC2 filter set. These flat fields will allow mapping of the

OTA illumination pattern and will be used in conjunction with previous

internal and external flats to generate new pipeline superflats. These

Earth flats will complement the Earth flat data obtained during cycles

4-14.

WFPC2 11081

RR Lyrae stars in M31 Globular Clusters: How did the M31 Spiral Galaxy

Form?

The pulsation properties of the RR Lyrae stars in the globular clusters

of the Andromeda galaxy {M31} have the potential to provide essential

insight on the first epoch of the galaxy formation and to trace the

merging episodes that led to the assembly of M31. Their mean periods

along with the cluster metallicities can provide an independent estimate

of the M31 cluster ages and, in turn, of the time scale of the M31 halo

formation, by comparison with their Milky Way counterparts. We will

observe RR Lyrae stars in 6 appropriately selected globular clusters of

M31 using WFPC2 to derive periods, light curves, and physical parameters

of these eyewitnesses of the first epochs of the M31 formation.

WFPC2 11084

Probing the Least Luminous Galaxies in the Local Universe

We propose to obtain deep color-magnitude data of eight new Local Group

galaxies which we recently discovered: Andromeda XI, Andromeda XII, and

Andromeda XIII {satellites of M31}; Canes Venatici I, Canes Venatici II,

Hercules, and Leo IV {satellites of the Milky Way}; and Leo T, a new

"free-floating" Local Group dwarf spheroidal with evidence for recent

star formation and associated H I gas. These represent the least

luminous galaxies known at *any* redshift, and are the only accessible

laboratories for studying this extreme regime of galaxy formation. With

deep WFPC-2 F606W and F814W pointings at their centers, we will

determine whether these objects contain single or multiple age stellar

populations, as well as whether these objects display a range of

metallicities.

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 11229

SEEDS: The Search for Evolution of Emission from Dust in Supernovae with

HST and Spitzer

The role that massive stars play in the dust content of the Universe is

extremely uncertain. It has long been hypothesized that dust can

condense within the ejecta of supernovae {SNe}, however there is a

frustrating discrepancy between the amounts of dust found in the early

Universe, or predicted by nucleation theory, and inferred from SN

observations. Our SEEDS collaboration has been carefully revisiting the

observational case for dust formation by core-collapse SNe, in order to

quantify their role as dust contributors in the early Universe. As dust

condenses in expanding SN ejecta, it will increase in optical depth,

producing three simultaneously observable phenomena: {1} increasing

optical extinction; {2} infrared {IR} excesses; and {3} asymmetric

blue-shifted emission lines. Our SEEDS collaboration recently reported

all three phenomena occurring in SN2003gd, demonstrating the success of

our observing strategy, and permitting us to derive a dust mass of up to

0.02 solar masses created in the SN. To advance our understanding of the

origin and evolution of the interstellar dust in galaxies, we propose to

use HST's WFPC2 and NICMOS instruments plus Spitzer's photometric

instruments to monitor ten recent core- collapse SNe for dust formation

and, as a bonus, detect light echoes that can affect the dust mass

estimates. These space-borne observations will be supplemented by

ground- based spectroscopic monitoring of their optical emission line

profiles. These observations would continue our 2-year HST and Spitzer

monitoring of this phenomena in order to address two key questions: Do

all SNe produce dust? and How much dust do they produce? As all the SN

are within 15 Mpc, each SN stands an excellent chance of detection with

HST and Spitzer and of resolving potential light echoes.

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 30                   30              

SIGNIFICANT EVENTS: (None)