HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT       # 4301

PERIOD COVERED: UT February 15, 2007 (DOY 046)

OBSERVATIONS SCHEDULED

WFPC2 10520

Resolving the Complex Star Formation History of the Leo I Dwarf

Spheroidal Galaxy

Determining the star formation histories {SFHs} and chemical evolution

of nearby galaxies gives us powerful constrains on the physical

processes that regulate galaxy evolution. The SFHs can be measured most

accurately by comparing the observed densities of stars in

color-magnitude diagrams {CMDs} to predictions from stellar evolutionary

models. WFPC2 imaging of the Leo I dSph shows it is unique because its

stellar population is relatively young. Approximately 68% of its stars

formed between 1 and 7 Gyr ago and only 12% of its stars formed >~ 10

Gyr ago. We propose to vastly improve the derived SFH of Leo I by

exploiting ACS/WFC's higher quantum efficiency at bluer wavelengths,

higher spatial resolution, and larger field-of-view. The figure of merit

for our proposed observations, defined as the age resolution times the

number of stars detected, will be a factor of 12 higher than existing

WFPC2 observations. To surmount the degeneracy of age and metallicity in

the CMD, we have independently measured the metallicity distribution of

its stars using spectroscopy. Simultaneously modeling the metallicity

distribution and CMD, we will firmly constrain the evolution of the Leo

I dSph, a unique example of an isolated dwarf galaxy that has not been

influenced by interactions with the Milky Way or M31.

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 DARKSs. 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 11082

NICMOS Imaging of GOODS: Probing the Evolution of the Earliest Massive

Galaxies, Galaxies Beyond

Deep near-infrared imaging provides the only avenue towards

understanding a host of astrophysical problems, including: finding

galaxies and AGN at z > 7, the evolution of the most massive galaxies,

the triggering of star formation in dusty galaxies, and revealing

properties of obscured AGN. As such, we propose to observe 60 selected

areas of the GOODS North and South fields with NICMOS Camera 3 in the

F160W band pointed at known massive M > 10^11 M_0 galaxies at z > 2

discovered through deep Spitzer imaging. The depth we will reach {26.5

AB at 5 sigma} in H_160 allows us to study the internal properties of

these galaxies, including their sizes and morphologies, and to

understand how scaling relations such as the Kormendy relationship

evolved. Although NIC3 is out of focus and undersampled, it is currently

our best opportunity to study these galaxies, while also sampling enough

area to perform a general NIR survey 1/3 the size of an ACS GOODS field.

These data will be a significant resource, invaluable for many other

science goals, including discovering high redshift galaxies at z > 7,

the evolution of galaxies onto the Hubble sequence, as well as examining

obscured AGN and dusty star formation at z > 1.5. The GOODS fields are

the natural location for HST to perform a deep NICMOS imaging program,

as extensive data from space and ground based observatories such as

Chandra, GALEX, Spitzer, NOAO, Keck, Subaru, VLT, JCMT, and the VLA are

currently available for these regions. Deep high-resolution

near-infrared observations are the one missing ingredient to this

survey, filling in an important gap to create the deepest, largest, and

most uniform data set for studying the faint and distant universe. The

importance of these images will increase with time as new facilities

come on line, most notably WFC3 and ALMA, and for the planning of future

JWST observations.

WFPC2 10871

Observations of the Galilean Satellites in Support of the New Horizons

Flyby

On February 28 2007 the New Horizons {NH} spacecraft will fly by Jupiter

on its way to Pluto, and will conduct an extensive series of

observations of the Jupiter system, including the Galilean satellites.

We propose HST observations to support and complement the New Horizons

observations in four ways: 1} Determine the distribution and variability

of Io's plumes in the two weeks before NH closest approach, to look for

correlations with Io- derived dust streams that may be detected by New

Horizons, to understand the origin of the dust streams; 2} Imaging of

SO2 and S2 gas absorption in Io's plumes in Jupiter transit, which

cannot be done by NH; 3} Color imaging of Io's surface to determine the

effects of the plumes and volcanos seen by New Horizons on the surface-

New Horizons cannot image the sunlit surface in color due to saturation;

4} Imaging of far-UV auroral emissions from the atmospheres of Io,

Europa, and Ganymede in Jupiter eclipse, near- simultaneously with

disk-integrated NH UV spectra, to locate the source of the UV emissions

seen by NH and use the response of the satellite atmospheres to the

eclipse to constrain production mechanisms.

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 11089

WFPC2 UV Throughput Check after 27-Jan-2007 Safemode

Check UV throughput of standard star GRW+70D5824 in all four chips

following safemode caused by ACS Side 2 failure.

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               10                  10                                                                                                                                 

FGS REacq               05                  05

OBAD with Maneuver 30                  30               

SIGNIFICANT EVENTS:

Flash Report: ACS Side-1 Switch and SBC-Only Operations

The Flight Readiness Review for the switch to ACS Side-1 and subsequent

SBC-Only Operations was held on 15 February 2007 (DOY 046). Authority

was given to proceed with the first two steps of switching to Side-1,

which consist of establishing ACS in its Side-1 Safing configuration and

updating the SMAC20. Ops Requests #18018 and #18017 will be executed

between 047/15:54 and 047/16:39.

Further ACS Side-1 reconfigurations will stand down until the ST ScI

reports their analysis of WFPC2 UV Images. A telephone tag-up is planned

for noon, February 16, for the ST ScI to report their findings. The

remaining ACS transitions are planned to be executed between 047/18:00

and 048/02:25, pending HST Project approval at the tag-up telecon.