Status Report

NASA Hubble Space Telescope Status Update #4801

By SpaceRef Editor
March 5, 2009
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HUBBLE SPACE TELESCOPE DAILY REPORT #4801

Continuing to collect World Class Science

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)

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