HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science



DAILY REPORT #4765



PERIOD COVERED: 5am January 5 - 5am January 6, 2009 (DOY

005/1000z-006/1000z)



OBSERVATIONS SCHEDULED



FGS 11704



The Ages of Globular Clusters and the Population II Distance Scale



Globular clusters are the oldest objects in the universe whose age can

be accurately determined. The dominant error in globular cluster age

determinations is the uncertain Population II distance scale. We propose

to use FGS 1r to obtain parallaxes with an accuracy of 0.2

milliarcsecond for 9 main sequence stars with [Fe/H] < -1.5. This will

determine the absolute magnitude of these stars with accuracies of 0.04

to 0.06mag. This data will be used to determine the distance to 24

metal-poor globular clusters using main sequence fitting. These

distances (with errors of 0.05 mag) will be used to determine the ages

of globular clusters using the luminosity of the subgiant branch as an

age indicator. This will yield absolute ages with an accuracy 5%, about

a factor of two improvement over current estimates. Coupled with

existing parallaxes for more metal-rich stars, we will be able to

accurately determine the age for globular clusters over a wide range of

metallicities in order to study the early formation history of the Milky

Way and provide an independent estimate of the age of the universe.



The Hipparcos database contains only 1 star with [Fe/H] < -1.4 and an

absolute magnitude error less than 0.18 mag which is suitable for use in

main sequence fitting. Previous attempts at main sequence fitting to

metal-poor globular clusters have had to rely on theoretical

calibrations of the color of the main sequence. Our HST parallax program

will remove this source of possible systematic error and yield distances

to metal-poor globular clusters which are significantly more accurate

than possible with the current parallax data. The HST parallax data will

have errors which are 10 times smaller than the current parallax data.

Using the HST parallaxes, we will obtain main sequence fitting distances

to 11 globular clusters which contain over 500 RR Lyrae stars. This will

allow us to calibrate the absolute magnitude of RR Lyrae stars, a

commonly used Population II distance indicator.



ACS/SBC 11236



Did Rare, Large Escape-Fraction Galaxies Reionize the Universe?



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 that

the escape fraction is close to zero in most galaxies, even among young

starbursts, but is large in 15-25% of them. Non-uniform escape fractions

are expected as a result of violent events creating clear paths in small

parts of galaxies. The number of galaxies observed with high escape

fraction will result from the combination of the intrinsic number with

clear lines of sight and their orientation with respect to the observer.

We propose to measure the fraction of escaping Lyman continuum radiation

in a large sample (47) of z~0.7 starbursts in the COSMOS field. These

compact UV-luminous galaxies are good analogs to high redshift LBGs.

Using the SBC/PR130L we can quickly (1-4 orbits) detect relative escape

fractions (f_LC/f_1500) of 25% or more. This will be the first

measurement of the escape fraction in sources between z=1 and the local

universe. We expect ~10 detections. Stacking will set limits of <4% on

the relative escape fraction in the rest. We will correlate the LC

detections with the properties of the galaxies. By



targeting z~0.7 in COSMOS, we will have tremendous ancillary information

on those sources. A non-detection in all sources would be significant

(99% confidence). This would imply that QSOs provide the overwhelming

majority of ionizing radiation at z<1, requiring substantial evolution

in the processes within Lyman break galaxies which allow large escape

fractions at high redshift.



WFPC2 11302



WFPC2 CYCLE 16 Standard Darks - Part III



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 11793



WFPC2 Cycle 16 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 11966



The Recent Star Formation History of SINGS Galaxies



The Spitzer Legacy project SINGS provided a unique view of the current

state of star formation and dust in a sample of galaxies of all Hubble

types. This multi-wavelength view allowed the team to create current

star formation diagnostics that are independent of the dust content and

increased our understanding of the dust in galaxies. Even so, using the

SINGS data alone we can only make rough estimates of the recent star

formation history of these galaxies. The lack of high resolution

observations (especially U-band and H-alpha) means that it is impossible

to estimate the ages of young clusters. In addition, the low resolution

of the Spitzer and ground-based observations means that what appear to

be individual Spitzer sources can actually be composed of many

individual clusters with varying ages. We need to know the ages, star

formation histories, and extinction of these individual clusters to

understand how these clusters form and age and thus influence the

evolution of the galaxy. In this proposal we address this missing area

of SINGS by obtaining high-resolution WFPC2 UBVI & H-alpha observations

to not only accurately locate and determine the ages of the young

stellar clusters in the actively star forming SINGS galaxies but to also

address a variety of other scientific issues. Over 500 HST orbits and

500 hours of Spitzter observing time have been dedicated to observations

of the SINGS sample. But the HST observations have not been systematic.

By adding a relatively small fraction of this time for these requested

observations, we will greatly enhance the legacy value of the SINGS

observations by creating a uniform high resolution multi-wavelength HST

archive that matches the quality of the lower resolution SINGS archive.



WFPC2 11967



WFPC2 Imaging of the Lockman Hole



In order to understand galaxy evolution and constrain theoretical

models, we require both multiwavelength photometry (to robustly

determine physical parameters such as star formation rates and stellar

masses) and detailed morphological information. Galaxy morphology

encodes crucial information about galaxy formation history and the

physical processes that trigger star formation and AGN activity, and

high-resolution imaging for large samples of galaxies is currently only

obtainable with HST. The Lockman Hole has been the target of extensive

multi-wavelength observations from the X-ray to the radio, and will be

the target of the deepest wide-area blankfield thermal IR observations

with Herschel, but currently lacks comprehensive HST imaging. We propose

to obtain WFPC2 imaging of ~500 arcmin2 of the central region of the

Lockman Hole in F606W and F814W, to a depth of V606~26.8 and I814~26.

This imaging is crucial in order to characterize the sources detected at

other wavelengths.



FLIGHT OPERATIONS SUMMARY:



Significant Spacecraft Anomalies: (The following are preliminary reports

of potential non-nominal performance that will be investigated.)



HSTARS:

11630 - REAcq(2,3,3) scheduled at 006/00:24:55z Failed to RGA HOLD at 006/0027:44z.

Observation affected WFPC 37 Proposal ID#11967



COMPLETED OPS REQUEST: (None)



COMPLETED OPS NOTES: (None)



SCHEDULED SUCCESSFUL

FGS GSacq 07 07

FGS REacq 07 06

OBAD with Maneuver 28 28



SIGNIFICANT EVENTS: (None)