HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT # 4517

PERIOD COVERED: UT Dec 31 - Jan 01, 2007 (DOY 365) - 2008 (DOY 001)

OBSERVATIONS SCHEDULED

ACS/SBC 11145

Probing the Planet Forming Region of T Tauri Stars in Chamaeleon

By studying the inner, planet-forming regions of circumstellar disks

around low-mass pre- main sequence stars we can refine theories of giant

planet formation and develop timescales for the evolution of disks and

their planets. Spitzer infrared observations of T Tauri stars in the

Chamaeleon star-forming region have given us an unprecedented look at

dust evolution in young objects. However, despite this ground breaking

progress in studying the dust in young disks, the gas properties of the

inner disk remain essentially unknown. Using ACS on HST, we propose to

measure the H_2 emission originating in the innermost disk regions of

classical T Tauri stars in different stages of evolution with the

objective of revealing the timescales of gas dissipation and its

relationship to dust evolution. This proposal is part of a comprehensive

effort with approved programs on Spitzer, Gemini, and Magellan that aim

to characterize the state of gas and dust in disks where planets may

already have formed.

WFPC2 10583

Resolving the LMC Microlensing Puzzle: Where Are the Lensing Objects ?

We are requesting 32 HST orbits to help ascertain the nature of the

population that gives rise to the observed set of microlensing events

towards the LMC. The SuperMACHO project is an ongoing ground-based

survey on the CTIO 4m that has demonstrated the ability to detect LMC

microlensing events in real-time via frame subtraction. The improvement

in angular resolution and photometric accuracy available from HST will

allow us to 1} confirm that the detected flux excursions arise from LMC

source stars rather than extended objects {such as for background

supernovae or AGN}, and 2} obtain reliable baseline flux measurements

for the objects in their unlensed state. The latter measurement is

important to resolve degeneracies between the event timescale and

baseline flux, which will yield a tighter constraint on the microlensing

optical depth.

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.

NIC3 11195

Morphologies of the Most Extreme High-Redshift Mid-IR-luminous Galaxies

II: The `Bump' Sources

The formative phase of some of the most massive galaxies may be

extremely luminous, characterized by intense star- and AGN-formation.

Till now, few such galaxies have been unambiguously identified at high

redshift, and thus far we have been restricted to studying the

low-redshift ultraluminous infrared galaxies as possible analogs. We

have recently discovered a sample of objects which may indeed represent

this early phase in galaxy formation, and are undertaking an extensive

multiwavelength study of this population. These objects are optically

extremely faint {R>26} but nevertheless bright at mid-infrared

wavelengths {F[24um] > 0.5 mJy}. Mid-infrared spectroscopy with

Spitzer/IRS reveals that they have redshifts z~2, implying luminosities

~1E13 Lsun. Their mid-IR SEDs fall into two broad, perhaps overlapping,

categories. Sources with brighter F[24um] exhibit power-law SEDs and SiO

absorption features in their mid-IR spectra characteristic of AGN,

whereas those with fainter F[24um] show a "bump" characteristic of the

redshifted 1.6um peak from a stellar population, and PAH emission

characteristic of starformation. We have begun obtaining HST images of

the brighter sources in Cycle 15 to obtain identifications and determine

kpc-scale morphologies for these galaxies. Here, we aim to target the

second class {the "bump" sources} with the goal of determining if these

constitute morphologically different objects, or simply a "low-AGN"

state of the brighter class. The proposed observations will help us

determine whether these objects are merging systems, massive obscured

starbursts {with obscuration on kpc scales!} or very reddened {locally

obscured} AGN hosted by intrinsically low-luminosity galaxies.

WFPC2 10890

Morphologies of the Most Extreme High-Redshift Mid-IR-Luminous Galaxies

The formative phase of the most massive galaxies may be extremely

luminous, characterized by intense star- and AGN-formation. Till now,

few such galaxies have been unambiguously identified at high redshift,

restricting us to the study of low-redshift ultraluminous infrared

galaxies as possible analogs. We have recently discovered a sample of

objects which may indeed represent this early phase in galaxy formation,

and are undertaking an extensive multiwavelength study of this

population. These objects are bright at mid-IR wavelengths

{F[24um]>0.8mJy}, but deep ground based imaging suggests extremely faint

{and in some cases extended} optical counterparts {R~24-27}. Deep K-band

images show barely resolved galaxies. Mid-infrared spectroscopy with

Spitzer/IRS reveals that they have redshifts z ~ 2-2.5, suggesting

bolometric luminosities ~10^{13-14}Lsun! We propose to obtain deep ACS

F814W and NIC2 F160W images of these sources and their environs in order

to determine kpc-scale morphologies and surface photometry for these

galaxies. The proposed observations will help us determine whether these

extreme objects are merging systems, massive obscured starbursts {with

obscuration on kpc scales!} or very reddened {locally obscured} AGN

hosted by intrinsically low-luminosity galaxies.

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 11179

Dynamics of Clumpy Supersonic Flows in Stellar Jets and in the

Laboratory

We propose to reobserve three stellar jets in order to quantify how

rapidly clumps in these flows accelerate and decelerate, and to compare

the results with ongoing numerical simulations and laboratory

experiments. Each jet has been imaged twice before with HST, and precise

proper motions have been measured for all emitting knots in the jets.

Images from the first two epochs show clear differential motions between

adjacent clumps, as well as shear, and possibly fragmentation. The

proposed third epoch will enable us to measure the first ever

accelerations in jets, quantify errors in existing proper motion

measurements, and observe in real time how fluid instabilities develop

in supersonic flows. The new images will make it possible to compare the

behavior of astrophysical flows directly with numerical simulations and

with laboratory experiments of bow shocks and clumpy flows in progress

at the Omega laser facility.

WFPC2 11327

Red leaks

The aim of this program is to measure the red leaks in the 8 WFPC2 UV???

filters (F122M, F300W, F255W, F218W, F185W, F170W, F160BW, F122M). We

will use red crossing filters to isolate and directly measure the leaks.

No observations of this kind have ever been performed with WFPC2 to

check the red leaks in the UV filters, most of them being extensively

used by GO/GTO programs. A previous calibration program has only imaged

spectrophotometric standard stars with UV filters (no filter crossing)

thus the red leak is hard to measure using this data. The throughput

curves for some of the UV filters (F300W, F255W, F218W, F185W) in

synphot have incomplete information, some of them have gaps in the

measurements as wide as 3000A.

FGS 11211

An Astrometric Calibration of Population II Distance Indicators

In 2002 HST produced a highly precise parallax for RR Lyrae. That

measurement resulted in an absolute magnitude, M{V}= 0.61+/-0.11, a

useful result, judged by the over ten refereed citations each year

since. It is, however, unsatisfactory to have the direct,

parallax-based, distance scale of Population II variables based on a

single star. We propose, therefore, to obtain the parallaxes of four

additional RR Lyrae stars and two Population II Cepheids, or W Vir

stars. The Population II Cepheids lie with the RR Lyrae stars on a

common K-band Period-Luminosity relation. Using these parallaxes to

inform that relationship, we anticipate a zero-point error of 0.04

magnitude. This result should greatly strengthen confidence in the

Population II distance scale and increase our understanding of RR Lyrae

star and Pop II Cepheid astrophysics.

FGS 11213

Distances to Eclipsing M Dwarf Binaries

We propose HST FGS observations to measure accurate distances of 5

nearby M dwarf eclipsing binary systems, from which model-independent

luminosities can be calculated. These objects have either poor or no

existing parallax measurements. FGS parallax determinations for these

systems, with their existing dynamic masses determined to better than

0.5%, would serve as model-independent anchor points for the low-mass

end of the mass-luminosity diagram.