Status Report

NASA Hubble Space Telescope Daily Report #4175

By SpaceRef Editor
August 11, 2006
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NASA Hubble Space Telescope Daily Report #4175

HUBBLE SPACE TELESCOPE – Continuing to collect World Class Science


PERIOD COVERED: UT August 10, 2006 (DOY 222)


ACS/HRC 10860

The largest Kuiper belt object

The past year has seen an explosion in the discoveries of Pluto-sized objects in the Kuiper belt. With the discoveries of the methane-covered 2003 UB313 and 2005 FY9, the multiple satellite system of 2003 EL61, and the Pluto-Charon analog system of Orcus and its satellite, it is finally apparent that Pluto is not a unique oddball at the edge of the solar system, but rather one of a family of similarly large objects in the Kuiper belt and beyond. HST observations over the past decade have been critical for understanding the interior, surface, and atmosphere of Pluto and Charon. We propose here a comprehensive series of observations designed to similarly expand our knowledge of these recently discovered Pluto-sized and near-Pluto-sized Kuiper belt objects. These observations will measure objects’ sizes and densities, explore the outcome of collisions in the outer solar system, and allow the first ever look at the interior structure of a Kuiper belt object. Our wide field survey that discovered all of these objects is nearly finished, so after five years of continuous searching we are finally almost complete in our tally of these near-Pluto-sized objects. This large HST request is the culmination of this half-decade search for new planetary-sized objects. As has been demonstrated repeatedly by the approximately 100 previous orbits devoted to the study of Pluto, only HST has the resolution and sensitivity for detailed study of these distant objects. With these new Pluto-sized objects only now being discovered we have a limited window left to still use HST for these critical observations.


CCD Hot Pixel Annealing

Hot pixel annealing will continue to be performed once every 4 weeks. The CCD TECs will be turned off and heaters will be activated to bring the detector temperatures to about +20C. This state will be held for approximately 6 hours, after which the heaters are turned off, the TECs turned on, and the CCDs returned to normal operating condition. To assess the effectiveness of the annealing, a bias and four dark images will be taken before and after the annealing procedure for both WFC and HRC. The HRC darks are taken in parallel with the WFC darks. The charge transfer efficiency {CTE} of the ACS CCD detectors declines as damage due to on-orbit radiation exposure accumulates. This degradation has been closely monitored at regular intervals, because it is likely to determine the useful lifetime of the CCDs. We combine the annealling activity with the charge transfer efficiency monitoring and also merge into the routine dark image collection. To this end, the CTE monitoring exposures have been moved into this proposal . All the data for this program is acquired using internal targets {lamps} only, so all of the exposures should be taken during Earth occultation time {but not during SAA passages}. This program emulates the ACS pre-flight ground calibration and post-launch SMOV testing {program 8948}, so that results from each epoch can be directly compared. Extended Pixel Edge Response {EPER} and First Pixel Response {FPR} data will be obtained over a range of signal levels for both the Wide Field Channel {WFC}, and the High Resolution Channel {HRC}.

ACS/WFC 10787

Modes of Star Formation and Nuclear Activity in an Early Universe Laboratory

Nearby compact galaxy groups are uniquely suited to exploring the mechanisms of star formation amid repeated and ongoing gravitational encounters, conditions similar to those of the high redshift universe. These dense groups host a variety of modes of star formation, and they enable fresh insights into the role of gas in galaxy evolution. With Spitzer mid-IR observations in hand, we have begun to obtain high quality, multi-wavelength data for a well-defined sample of 12 nearby {<4500km/s} compact groups covering the full range of evolutionary stages. Here we propose to obtain sensitive BVI images with the ACS/WFC, deep enough to reach the turnover of the globular cluster luminosity function, and WFPC2 U-band and ACS H-alpha images of Spitzer- identified regions hosting the most recent star formation. In total, we expect to detect over 1000 young star clusters forming inside and outside galaxies, more than 4000 old globular clusters in

>40 giant galaxies {including 16 early-type galaxies}, over 20 tidal

features, approximately 15 AGNs, and intragroup gas in most of the 12 groups. Combining the proposed ACS images with Chandra observations, UV GALEX observations, ground-based H-alpha imaging, and HI data, we will conduct a detailed study of stellar nurseries, dust, gas kinematics, and AGN. ACS/WFC 10816

The Formation History of Andromeda’s Extended Metal-Poor Halo

We propose deep ACS imaging in the outer spheroid of the Andromeda galaxy, in order to measure the star formation history of its true halo. For the past 20 years, nearly all studies of the Andromeda “halo” were focused on the spheroid within 30 kpc of the galaxy’s center, a region now known to host significant substructure and populations with high metallicity and intermediate ages. However, two groups have recently discovered an extended metal-poor halo beyond 30 kpc; this population is distinct in its surface-brightness profile, abundance distribution, and kinematics. In earlier cycles, we obtained deep images of the inner spheroid {11 kpc on the minor axis}, outer disk {25 kpc on the major axis}, and giant tidal stream, yielding the complete star formation history in each field. We now propose deep ACS imaging of 4 fields bracketing this 30 kpc transition point in the spheroid, so that the inner spheroid and the extended halo populations can be disentangled, enabling a reconstruction of the star formation history in the halo. A wide age distribution in the halo, as found in the inner spheroid, would imply the halo was assembled through ongoing accretion of satellite galaxies, while a uniformly old population would be a strong indication that the halo was formed during the early rapid collapse of the Andromeda proto-galaxy.

FGS 10611

Precise Distances to Nearby Planetary Nebulae

We propose to carry out astrometry with the FGS to obtain accurate and precise distances to four nearby planetary nebulae. In 1992, Cahn et al. noted that “The distances to Galactic planetary nebulae remain a serious, if not THE most serious, problem in the field, despite decades of study.” Twelve years later, the same statement still applies. Because the distances to planetary nebulae are so uncertain, our understanding of their masses, luminosities, scale height, birth rate, and evolutionary state is severely limited. To help remedy this problem, HST astrometry can guarantee parallaxes with half the error of any other available approach. These data, when combined with parallax measurements from the USNO, will improve distance measurements by more than a factor of two, producing more accurate distances with uncertainties that are of the order of ~6%. Lastly, most planetary nebula distance scales in the literature are statistical. They require several anchor points of known distance in order to calibrate their zero point. Our program will provide “gold standard” anchor points by the end of 2006, a decade before any anticipated results from future space astrometry missions.

NIC1 10879

A search for planetary-mass companions to the nearest L dwarfs – completing the survey

We propose to extend the most sensitive survey yet undertaken for very low-mass companions to ultracool dwarfs. We will use NICMOS to complete imaging of an all-sky sample of 87 L dwarfs in 80 systems within 20 parsecs of the Sun. The combination of infrared imaging and proximity allows us to search for companions with mass ratios q>0.25 at separations exceeding ~3 AU, while probing companions with q>0.5 at ~1.5 AU separation. This resolution is crucial, since no ultracool binaries are known in the field with separations exceeding 15 AU. Fifty L dwarfs from the 20-parsec sample have high-resolution imaging, primarily through our Cycle 13 HST proposal which identified six new binaries, including an L/T system. Here, we propose to target the remaining 30 dwarfs

NIC1/NC2/NC3 10723

Cycle 14 NICMOS dark current, shading profile, and read noise monitoring program

The purpose of this proposal is to monitor the dark current, read noise, and shading profile for all three NICMOS detectors throughout the duration of Cycle 14. This proposal is a slightly modified version of proposal 10380 of cycle 13 and 9993 of cycle12 that we cut down some exposure time to make the observation fit within 24 orbits.

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.

NIC2 10847

Coronagraphic Polarimetry of HST-Resolved Debris Disks

We propose to take full advantage of the recently commissioned coronagraphic polarimetry modes of ACS and NICMOS to obtain imaging polarimetry of circumstellar debris disks that were imaged previously by the HST coronagraphs, but without the polarizers. It is well established that stars form in gas-rich protostellar disks, and that the planets of our solar system formed from a circum-solar disk. However, the connection between the circumstellar disks that we observe around other stars and the processes of planet formation is still very uncertain. Mid-IR spectral studies have suggested that disk grains are growing in the environments of young stellar objects during the putative planet-formation epoch. Furthermore, structures revealed in well resolved images of circumstellar disks suggest gravitational influences on the disks from co-orbital bodies of planetary mass. Unfortunately, existing imaging data provides only rudimentary information abou the disk grains and their environments. Our proposed observations, which can be obtained only with HST, will enable us to quantitatively determine the sizes of the grains and optical depths as functions of their location within the disks {i.e., detailed tomography}. Armed with these well-determine physical and geometrical systemic parameters, we will develop a set of self-consistent models of disk structures to investigate possible interactions between unseen planets and the disks from which they formed. Our results will also calibrate models of the thermal emission from these disks, that will in turn enable us to infer the properties of other debris disks that cannot be spatially resolved with current or planned instruments and telescopes.

WFPC2 10631

Intermediate-Age Globular Clusters in M31

We propose deep ACS/WFC imaging of four halo M31 globular clusters in order to derive their horizontal branch morphologies. Our spectroscopic investigation of their integrated light identifies them as members of an intermediate-age population of globular clusters in M31. Since our spectroscopic results are based on the analysis of Balmer absorption lines, we need to secure our results against an artificial juvenation due to extreme horizontal branch morphologies. The proposed observations will allow a clear-cut answer to the question of whether spectroscopically derived intermediate-age estimates are due to genuinely younger ages or are the result of anomalously hot horizontal branch morphologies. Either way, our results will have important implications for spectroscopically derived ages and metallicities of distant stellar populations. Because of the high spatial resolution of the proposed ACS/WFC observations we will also derive accurate surface brightness profiles of our target globular clusters and investigate the influence of stellar density on horizontal branch morphology. Moreover, together with deep parallel WFPC2 fields we will study the metallicity dispersion of the background stellar population in M31 as a function of galactocentric radius.


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

HSTARS: (None)



                          SCHEDULED      SUCCESSFUL 
FGS GSacq                07                     07 
FGS REacq                07                     07 
OBAD with Maneuver   28                     28 


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