HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT       #4801

PERIOD COVERED: 5am February 27 - 5am March 2, 2009 (DOY

                             058/1000z-061/1000z)

OBSERVATIONS SCHEDULED

WFPC2 11986

Completing HST's Local Volume Legacy

Nearby galaxies offer one of the few laboratories within which stellar

populations can be tied to multi-wavelength observations. They are thus

essential for calibrating and interpreting key astrophysical

observables, such as broad-band luminosities, durations and energy input

from starbursts, and timescales of UV, H-alpha, and FIR emission. The

study of stellar populations in nearby galaxies requires high-resolution

observations with HST, but HST's legacy for this limited set of galaxies

remains incomplete.

As a first attempt to establish this legacy, The ACS Nearby Galaxy

Survey Treasury (ANGST) began observations in late 2006. ANGST was

designed to carry out a uniform multi-color survey of a volume-limited

sample of ~70 nearby galaxies that could be used for systematic studies

of resolved stellar populations. The resulting data provide nuanced

constraints on the processes which govern star formation and galaxy

evolution, for a well-defined population of galaxies. All photometry for

the survey has been publicly released.

However, the failure of ACS 4.5 months after ANGST began taking data led

to a drastic reduction in the planned survey. The loss is two-fold.

First, the goals of completeness and uniformity were greatly

compromised, impacting global comparison studies. Second, the variety of

observed star formation histories was reduced. Given that we have never

found two galaxies with identical star formation histories, and fully

sampling the population allows us to catch those few systems whose star

formation rates and metallicities place the strongest constraints on key

astrophysical processes.

Here we propose WFPC2 observations of all remaining galaxies within the

Local Volume (D<3.5Mpc) for which current HST observations are

insufficient for meaningful stellar population studies. We will use

these observations for research on the star formation histories of

individual galaxies and the Local Volume, detailed calibrations of star

formation rate indicators, and the durations of starbursts. We will also

make them publicly available through the ANGST archive to support future

research. The proposed observations will finally complete a lasting

legacy of HST

ACS/SBC 11984

Observing Saturn's High Latitude Polar Auroras

Planetary auroral emissions are critical indicators of how the

magnetospheres of the planets work. Recently, a new component of

Saturn's auroral emissions, i.e. high latitude auroras inside the main

auroral oval, have been observed by the Cassini spacecraft during

otherwise quiet auroral conditions. Such high latitude auroras are of

immense interest since they occur on magnetic flux tubes connected to a

region that is key to the overall dynamics of the system, the

magnetotail, and where if conventional theories regarding Saturn's

magnetosphere are correct there should not be any auroras. These faint

auroral emissions have not been previously observed by the Hubble Space

Telescope (HST). However, the unique oblique viewing geometry afforded

during early 2009 due to Saturn's orbital longitude will result in the

apparent brightening of these polar emissions due to the

limb-brightening effect, with the result that they may be observable by

HST for the first ever time. In addition, at this time the Cassini

spacecraft will be in a high latitude orbit, with a trajectory that will

take it through these magnetic flux tubes, providing essential

simultaneous in situ data. This is the last time Cassini will be in such

an orbit during its mission as currently scheduled and HST is the only

instrument capable of obtaining sustained long-term observations of

Saturn's auroras. These observations will address the following:

Does Saturn exhibit high latitude UV auroras observable by HST? Where do

these auroras occur, and at what altitude? How do these auroras behave

over time? How variable are they? Are they periodic? How do they behave

with respect to other auroral components? What processes drive these

auroras?

Are these auroras generated by processes internal to the magnetosphere

or are they driven by the solar wind? How do the infrared (IR) auroras

relate to the ultraviolet (UV) auroras?

WFPC2 11983

An Imaging Survey of Protoplanetary Disks and Brown Dwarfs in the

Chamaeleon I region

We propose to carry out a HST/WFPC2 survey of young brown dwarfs, Class

I and Class II sources in the Chamaelon I region, one of the

best-studied star-forming regions, in order to investigate the link

between disk evolution and the formation of substellar-mass objects. We

will use deep broad-band imaging in the I and z-equivalent HST bands to

unveil the unknown population of substellar binary companions, down to a

few Jupiter masses for separations of a few tens of AU. We will also

perform narrow-band imaging to directly detect accreting circumstellar

disks and jets around brown dwarfs, Class-I and class-II objects.

Chamaelon I is nearly coeaval of Orion (~1-2Myr) but at ~1/3 its

distance, allowing 3x higher resolution and 10x more flux for comparable

objects. Unlike Orion, low-mass objects and protoplanetary disks in

Chamaeleon I have been extensively studied with Spitzer, but not yet

with the HST. The Chamaeleon I region is an ideal HST target, as it lies

in the CVZ of the HST and therefore it is easily accessible any time of

the year with long orbits.

WFPC2 11972

Investigating the Early Solar System with Distant Comet Nuclei

We propose 85 orbits of imaging observations with the WFPC2 to get

nucleus size estimates for 8 well observed dynamically new and

long-period comets at large distances from the sun when their activity

levels are low. This will increase the sample of these nucleus sizes by

nearly 50%, but will more than double the selection of comets for which

we can run thermal models. Small icy bodies are the best preserved

remnants of planet formation, and we have recently found that

observationally constrained thermal models can distinguish differences

in microphysical properties of comet nuclei. The new HST data will

enable the first exploration of physical conditions in different regions

of the early solar nebula.

WFPC2 11944

Binaries at the Extremes of the H-R Diagram

We propose to use HST/Fine Guidance Sensor 1r to survey for binaries

among some of the most massive, least massive, and oldest stars in our

part of the Galaxy. FGS allows us to spatially resolve binary systems

that are too faint to observe using ground-based, speckle or optical

long baseline interferometry, and too close to resolve with AO. We

propose a SNAP-style program of single orbit FGS TRANS mode observations

of very massive stars in the cluster NGC 3603, luminous blue variables,

nearby low mass main sequence stars, cool subdwarf stars, and white

dwarfs. These observations will help us to (1) identify systems suitable

for follow up studies for mass determination, (2) study the role of

binaries in stellar birth and in advanced evolutionary states, (3)

explore the fundamental properties of stars near the main sequence-brown

dwarf boundary, (4) understand the role of binaries for X-ray bright

systems, (5) find binaries among ancient and nearby subdwarf stars, and

(6) help calibrate the white dwarf mass - radius relation.

WFPC2 11797

Supplemental WFPC2 CYCLE 16 Intflat Linearity Check and Filter Rotation

Anomaly Monitor

Supplemental observations to 11029, to cover period from Aug 08 to SM4.

Intflat observations will be taken to provide a linearity check: the

linearity test consists of a series of intflats in F555W, in each gain

and each shutter. A combination of intflats, visflats, and earthflats

will be used to check the repeatability of filter wheel motions.

(Intflat sequences tied to decons, visits 1-18 in prop 10363, have been

moved to the cycle 15 decon proposal 11022 for easier scheduling.)

Note: long-exposure WFPC2 intflats must be scheduled during ACS anneals

to prevent stray light from the WFPC2 lamps from contaminating long ACS

external exposures.

Note: These are supplemental observations to cover June to SM4 (Oct 8

'08) + 6 months.

WFPC2 11795

WFPC2 Cycle 16 UV Earth Flats

Monitor flat field stability. This proposal obtains sequences of earth

streak flats to improve the quality of pipeline flat fields for the

WFPC2 UV filter set. These Earth flats will complement the UV earth flat

data obtained during cycles 8-15.

WFPC2 11794

Cycle 16 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

4-15.

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 11681

A Search for Ultraviolet Emission Filaments in Cool Core Clusters

We propose to use ACS SBC imaging to seek ultraviolet CIV emission

filaments in clusters of galaxies exhibiting strong cool-core X-ray

emission and optical line emission filaments. These short observations

are crafted to test thermal conduction models for the filament

excitation, and can significantly impact our understanding of the

overall physical processes dominant in the galaxy cluster ISM.

FGS 11298

Calibrating Cosmological Chronometers: White Dwarf Masses

We propose to use HST/FGS1R to determine White Dwarf {WD} masses. The

unmatched resolving power of HST/FGS1R will be utilized to follow up

four selected WD binary pairs. This high precision obtained with

HST/FGS1R simply cannot be equaled by any ground based technique. This

proposed effort complements that done by CoI Nelan in which a sample of

WDs is being observed with HST/FGS1R. This proposal will dramatically

increase the number of WDs for which dynamical mass measurements are

possible, enabling a better calibration of the WD mass-radius relation,

cooling curves, initial to final mass relations, and ultimately giving

important clues to the star formation history of our Galaxy and the age

of its disk as well as in other galaxies. {This project is part of

Subasavage's PhD thesis work at Georgia State University.}

FLIGHT OPERATIONS SUMMARY:

Significant Spacecraft Anomalies: (The following are preliminary reports

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

HSTARS:

11702 - GSAcq (2,1,2) results in fine lock backup (2,0,2) using FGS-2 @060/07:50:13z

              Observations possibly affected: WFPC #58-73, Proposal ID#11983.

COMPLETED OPS REQUEST: (None)

COMPLETED OPS NOTES: (None)

                          SCHEDULED      SUCCESSFUL

FGS GSAcq                  23              23                              

FGS REAcq                   12              12                 

OBAD with Maneuver    70              70

SIGNIFICANT EVENTS: (None)