Status Report

NASA Hubble Space Telescope Daily Report #4787

By SpaceRef Editor
February 16, 2009
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Continuing to collect World Class Science

PERIOD COVERED: 5am February 6 – 5am February 9, 2009 (DOY 037/1000z-040/1000z)


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 11967

WFPC2 Imaging of the Lockman Hole

In order to understand galaxy evolution and constrain theoretical models, we require both multiwavelength photometry (to robustly determine physical parameters such as star formation rates and stellar masses) and detailed morphological information. Galaxy morphology encodes crucial information about galaxy formation history and the physical processes that trigger star formation and AGN activity, and high-resolution imaging for large samples of galaxies is currently only obtainable with HST. The Lockman Hole has been the target of extensive multi-wavelength observations from the X-ray to the radio, and will be the target of the deepest wide-area blankfield thermal IR observations with Herschel, but currently lacks comprehensive HST imaging. We propose to obtain WFPC2 imaging of ~500 arcmin2 of the central region of the Lockman Hole in F606W and F814W, to a depth of V606~26.8 and I814~26. This imaging is crucial in order to characterize the sources detected at other wavelengths.

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.

WFPC2 11962

A New Supernova in the Antennae; Narrowing in on the Hubble Constant and Dark Energy

A measurement of the Hubble constant to a precision of a few percent would be a powerful aid to the investigation of the nature of dark energy and a potent “end-to-end” test of the present cosmological model. In Cycle 15 we constructed a new, streamlined distance ladder utilizing high-quality type Ia supernova data and observations of Cepheids with HST in the near-IR to minimize the dominant sources of systematic uncertainty in past measurements of the Hubble constant and reduce its total uncertainty to a little under 5%. Here we propose to exploit this new route with a rare opportunity to begin reducing the remaining uncertainty. SN 2007sr in the Antennae (NGC 4038/9) is the rare SN Ia which is suitable for increasing the precision of small calibration sample of SNe Ia. Even rarer is that it is close enough that it’s Cepheids are within range of observing with WFPC2 (and NICMOS, should it return to life). But we need to act fast as the window of long visibility and fixed orient runs from mid-early December 2008 to early March 2009. We request 34 orbits with WFPC2 to find the Cepheids in the SN host. We also request 16 orbits to observe the Cepheids we find with Camera 2, F160W if NICMOS becomes available by April 2009 . (If NICMOS does not return we would forgo these observations and ask the TTRB to let us make them with our own WFC3-IR allocation, though we much prefer the smaller pixel size of NIC2).

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.

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.

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 11113

Binaries in the Kuiper Belt: Probes of Solar System Formation and Evolution

The discovery of binaries in the Kuiper Belt and related small body populations is powering a revolutionary step forward in the study of this remote region. Three quarters of the known binaries in the Kuiper Belt have been discovered with HST, most by our snapshot surveys. The statistics derived from this work are beginning to yield surprising and unexpected results. We have found a strong concentration of binaries among low-inclination Classicals, a possible size cutoff to binaries among the Centaurs, an apparent preference for nearly equal mass binaries, and a strong increase in the number of binaries at small separations. We propose to continue this successful program in Cycle 16; we expect to discover at least 13 new binary systems, targeted to subgroups where these discoveries can have the greatest impact.


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


11664 – Loss of Lock @ 037/11:08:53z

Following a successful REAcq(1,2,1) at 037/10:50:58z, loss of lock was observed at 11:08:03 with QF1STOPF, QF2STOPF and QSTOP flags set and take data flag down. Eight ACS #779 status buffer messages (Fold Mechanism Move while Take Data Flag is down) were received. A type 3 slew was in progress.

Observations possibly affected: ACS #12-13, Proposal ID#11970

11666 – REAcq(1,2,2) at 040/04:57:07z failed due to STOP Flag on FGS1 at 04:59:47z.

Observations affected: WFPC2 #8-9, Proposal ID#11966



                          SCHEDULED      SUCCESSFUL      FAILURE

FGS GSacq                20              20
FGS REacq                20              19
OBAD with Maneuver       80              80
LOSS of LOCK                                             


SpaceRef staff editor.