Status Report

NASA Hubble Space Telescope Daily Report #4777

By SpaceRef Editor
January 29, 2009
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Continuing to collect World Class Science

PERIOD COVERED: 5am January 23 – 5am January 26, 2009 (DOY 023/1000z-026/1000z)


ACS/SBC 11970

HST Observations of Titan’s Escaping Atmosphere in Transit and in Emission

We propose UV observations using the ACS/SBC of Titan’s extended escaping atmosphere for the Jan/Feb 2009 period of transits of Titan across Saturn. A combination of absorption of Saturn’s reflected solar UV emission in transit, and extended emissions primarily from H atoms away from transit, will yield new information about the structure of Titan’s extended upper atmosphere. These observations are expected to provide new constraints on theoretical models for a hydrodynamic flow of species through Titan’s exobase level, resulting from the interpretation of recent Cassini measurements at Titan.

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.

FGS 11964

Post FGS1r AMA-Adjustment: OFAD Check and Alignment Calibration, 2008

The FGS1 AMA optimization proposal (11963) leaves the AMA mirror in a new position, which shifts the FGS1r FOV relative to FGS2r and FGS3 and has the potential to change the FGS1r OFAD solution. This proposal will use the astrometric open cluster NGC 5617 to check for 1 mas size changes in the OFAD and to establish the new alignment of FGS1r relative to FGS2r and FGS3 to a precision of approximately 25 mas. The OFAD check requires 4 HST orbits before, and 4 HST orbits after, the AMA adjustment. Each orbit observes the same stars in NGC 5617 with FGS1r in POS mode. The alignment aspect of this proposal uses data from these same orbits. The ICRS positions of the relevant stars are taken from the UCAC catalog, but the proper motions taken from the “special guide star plate ZZZT” provided by Yale University. We chose guide stars in FGS2r and FGS3, and astrometry targets that are common to GSC2, UCAC, and ZZZT. Each visit uses a unique guide star pair, so that all the visits taken together have guide stars spanning the guider FGSs FOV.

FGS 11943/11944

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 for 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.

FGS 11788

The Architecture of Exoplanetary Systems

Are all planetary systems coplanar? Concordance cosmogony makes that prediction. It is, however, a prediction of extrasolar planetary system architecture as yet untested by direct observation for main sequence stars other than the Sun. To provide such a test, we propose to carry out FGS astrometric studies on four stars hosting seven companions. Our understanding of the planet formation process will grow as we match not only system architecture, but formed planet mass and true distance from the primary with host star characteristics for a wide variety of host stars and exoplanet masses.

We propose that a series of FGS astrometric observations with demonstrated 1 millisecond of arc per-observation precision can establish the degree of coplanarity and component true masses for four extrasolar systems: HD 202206 (brown dwarf+planet); HD 128311 (planet+planet), HD 160691 = mu Arae (planet+planet), and HD 222404AB = gamma Cephei (planet+star). In each case the companion is identified as such by assuming that the minimum mass is the actual mass. For the last target, a known stellar binary system, the companion orbit is stable only if coplanar with the AB binary orbit.

WFPC2 11612

Eta Carinae’s Continuing Instability and Recovery – the 2009 Event

Eta Carinae is the only really observable example of structural recovery from a massive giant eruption, a “supernova imposter’ event. Moreover it is the only well-observed star above 100 Msun, and its 5.5-year-recurrent spectroscopic events provide extraordinary clues to its surface instability. This truly unique combination of attributes makes it valuable for understanding the most massive stars. A fresh development arose a few years ago: The star has brightened much faster than before, and appears to have entered a rapid stage in its post-eruption recovery.

A spectroscopic event will occur at 2009.0, soon after the planned HST servicing mission. Because of the recent secular trend, this event is expected to differ from its well-observed 2003.5 predecessor. The differences will be very important, because they offer clues to very-massive-star structural instabilities that can’t be observed in any other known way.

Some of the needed observations require HST’s high spatial resolution and UV coverage. We propose an efficient, well-chosen set of STIS and ACS observations around the critical time. If the servicing mission is too late for the event, then a subset of the observations will still be merited.

ACS/SBC 11579

The Difference Between Neutral- and Ionized-Gas Metal Abundances in Local Star-Forming Galaxies with COS

The metallicity of galaxies and its evolution with redshift is of paramount importance for understanding galaxy formation. Abundances in the interstellar medium (ISM) are typically determined using emission-line spectroscopy of HII regions. However, since HII regions are associated with recent SF they may not have abundances typical for the galaxy as a whole. This is true in particular for star-forming galaxies (SFGs), in which the bulk of the metals may be contained in the neutral gas. It is therefore important to directly probe the metal abundances in the neutral gas. This can be done using absorption lines in the Far UV. We have developed techniques to do this in SFGs, where the absorption is measured for sightlines toward bright SF regions within the galaxy itself. We have successfully applied this technique to a sample of galaxies observed with FUSE. The results have been very promising, suggesting in I Zw 18 that abundances in the neutral gas may be up to 0.5 dex lower than in the ionized gas. However, the interpretation of the FUSE data is complicated by the very large FUSE aperture (30 arcsec), the modest S/N, and the limited selection of species available in the FUSE bandpass. The advent of COS on HST now allows a significant advance in all of these areas. We will therefore obtain absorption line spectroscopy with G130M in the same sample for which we already have crude constraints from FUSE. We will obtain ACS/SBC images to select the few optimal sightlines to target in each galaxy. The results will be interpreted through line-profile fitting to determine the metal abundances constrained by the available lines. The results will provide important new insights into the metallicities of galaxies, and into outstanding problems at high redshift such as the observed offset between the metallicities of Lyman Break Galaxies and Damped Lyman Alpha systems.

ACS/SBC 11566

Imaging Saturn’s Equinoctal Auroras

Auroral emissions provide an indispensable diagnostic tool for the energetic processes occurring in planetary magnetospheres. In 2009 Saturn will reach equinox for the first time since the advent of high-sensitivity planetary ultraviolet (UV) auroral imaging, offering a unique, transient opportunity to observe both polar auroral regions simultaneously. The observations proposed here will not only provide the best images to date of Saturn’s northern auroras, they will address three fundamental issues: (1) Are Saturn’s auroras similar in the north and south? This will reveal the nature of the processes that cause the northern auroras, and verify the multipole nature of Saturn’s internal magnetic field. (2) Is the location of the northern auroral emission symmetric with to the south? This will indicate why the southern auroral oval is displaced a few degrees toward midnight from the spin pole. It will also reveal whether the oscillation observed in the location of the southern auroral oval is similarly observed in the north, illuminating the nature of near-planetary period oscillations observed throughout the magnetosphere and potentially providing a value for the elusive rotation period of the deep interior. (3) What is the influence of equinox on the magnetosphere? The unique orientation of the planetary spin axis at equinox will reveal whether the auroras are influenced by the direction of the interplanetary magnetic field, and whether the Sun’s effect on Saturn’s magnetosphere changes throughout the planet’s seasons. The Hubble Space Telescope is the only instrument capable of providing global instantaneous coverage of Saturn’s UV auroras, and since Saturn’s orbital period is ~30 years, Cycle 17 is the only opportunity to make these observations.

WFPC2 11289

SL2S: The Strong Lensing Legacy Survey

Recent systematic surveys of strong galaxy-galaxy lenses {CLASS, SLACS, GOODS, etc.} are producing spectacular results for galaxy masses roughly below a transition mass M~10^13 Mo. The observed lens properties and their evolution up to z~0.2, consistent with numerical simulations, can be described by isothermal elliptical potentials. In contrast, modeling of giant arcs in X-ray luminous clusters {halo masses M >~10^13 Mo} favors NFW mass profiles, suggesting that dark matter halos are not significantly affected by baryon cooling. Until recently, lensing surveys were neither deep nor extended enough to probe the intermediate mass density regime, which is fundamental for understanding the assembly of structures. The CFHT Legacy Survey now covers 125 square degrees, and thus offers a large reservoir of strong lenses probing a large range of mass densities up to z~1. We have extracted a list of 150 strong lenses using the most recent CFHTLS data release via automated procedures. Following our first SNAPSHOT proposal in cycle 15, we propose to continue the Hubble follow-up targeting a larger list of 130 lensing candidates. These are intermediate mass range candidates {between galaxies and clusters} that are selected in the redshift range of 0.2-1 with no a priori X-ray selection. The HST resolution is necessary for confirming the lensing candidates, accurate modeling of the lenses, and probing the total mass concentration in galaxy groups up to z~1 with the largest unbiased sample available to date.

WFPC2 11103

A Snapshot Survey of The Most Massive Clusters of Galaxies

We propose the continuation of our highly successful SNAPshot survey of a sample of 125 very X-ray luminous clusters in the redshift range 0.3-0.7. As demonstrated by the 25 snapshots obtained so far in Cycle14 and Cycle15 these systems frequently exhibit strong gravitational lensing as well as spectacular examples of violent galaxy interactions. The proposed observations will provide important constraints on the cluster mass distributions, the physical nature of galaxy-galaxy and galaxy-gas interactions in cluster cores, and a set of optically bright, lensed galaxies for further 8-10m spectroscopy. All of our primary science goals require only the detection and characterization of high-surface-brightness features and are thus achievable even at the reduced sensitivity of WFPC2. Because of their high redshift and thus compact angular scale our target clusters are less adversely affected by the smaller field of view of WFPC2 than more nearby systems. Acknowledging the broad community interest in this sample we waive our data rights for these observations.

WFPC2 10877

A Snapshot Survey of the Sites of Recent, Nearby Supernovae

During the past few years, robotic {or nearly robotic} searches for supernovae {SNe}, most notably our Lick Observatory Supernova Search {LOSS}, have found hundreds of SNe, many of them in quite nearby galaxies {cz < 4000 km/s}. Most of the objects were discovered before maximum brightness, and have follow-up photometry and spectroscopy; they include some of the best-studied SNe to date. We propose to conduct a snapshot imaging survey of the sites of some of these nearby objects, to obtain late-time photometry that {through the shape of the light and color curves} will help reveal the origin of their lingering energy. The images will also provide high-resolution information on the local environments of SNe that are far superior to what we can procure from the ground. For example, we will obtain color-color and color-magnitude diagrams of stars in these SN sites, to determine the SN progenitor masses and constraints on the reddening. Recovery of the SNe in the new HST images will also allow us to actually pinpoint their progenitor stars in cases where pre- explosion images exist in the HST archive. This proposal is an extension of our successful Cycle 13 snapshot survey with ACS. It is complementary to our Cycle 15 archival proposal, which is a continuation of our long-standing program to use existing HST images to glean information about SN environments.


Significant Spacecraft Anomalies: (The following are preliminary reports of potential non-nominal performance that will be investigated.)


11644 – At 023/21:06:13 GSAcq (2,3,2) scheduled from 023/21:03:13 – 21:10:28 failed to RGA Hold due to QF2STOPF and QSTOP flags on FGS-2.

Observation affected: Astrometry Proposal 11944

11645 – GSacq(1,2,2) at 025/03:41:59z failed to RGA control with Search Radius Limit exceeded on FGS 1.

Observations affected: WFPC #199-202 Proposal #11103.

11646 – GSacq(2,3,3) at 025/05:27:34z failed to RGA control with Search Radius Limit exceeded on FGS 2 at 025/05:32:25z.

Observations affected: Astrometry Proposal #11944.

11647 – GSacq(1,2,2) at 025/12:46:18 failed to RGA control at 12:51:13 with QF1STOPF and QSTOP flags set.

Observations affected: WFPC 203 to 206, proposal 10877.



                         SCHEDULED      SUCCESSFUL

FGS GSacq                24                  20
FGS REacq                13                  13
OBAD with Maneuver       74                  74


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