Status Report

NASA Hubble Space Telescope Daily Status Report #4194

By SpaceRef Editor
September 8, 2006
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NASA Hubble Space Telescope Daily Status Report #4194


PERIOD COVERED: UT September 07, 2006 (DOY 250)


ACS/HRC 10563

Accurate dark-matter mass profiles in 3 elliptical galaxies as a test of CDM

A critical test of the successful Lambda-CDM picture for structure formation is the measurement of the power law exponent, gamma, of the centre of dark matter density profiles, predicted to lie in the range 1.0-1.5. Measurements of gamma derived from rotation curves of LSB galaxies appear to contradict CDM, but rely on assumptions that are difficult to verify {e.g. axisymmetry}. We have recently demonstrated, using our new `semi-linear’ inversion method, how strong gravitational lensing by galaxies can provide a clean and accurate measurement of gamma, free of such ambiguities. HST images of lensed non-AGN galaxies provide hundreds of resolution elements, each a constraint on the mass profile. Such lenses are exceedingly rare, but we have recently discovered new systems. We propose deep ACS-HRC observations of 3 systems to measure gamma in each, accurate to 0.15 {95% confidence} and to obtain an indication of its variation between galaxies. To establish the required number of orbits we have undertaken an end-to-end simulation of the problem, creating and analysing synthetic ACS images. Additionally the semi-linear method simultaneously reconstructs the pixelised source surface brightness distribution. Our simulations demonstrate that the fine sampling and small pixel scattering of the HRC, resolves the morphology of the sources with exquisite detail.

ACS/HRC 10800

Kuiper Belt Binaries: Probes of Early Solar System Evolution

Binaries in the Kuiper Belt are a scientific windfall: in them we have relatively fragile test particles which can be used as tracers of the early dynamical evolution of the outer Solar System. We propose to continue a Snapshot program using the ACS/HRC that has a demonstrated discovery potential an order of magnitude higher than the HST observations that have already discovered the majority of known transneptunian binaries. With this continuation we seek to reach the original goals of this project: to accumulate a sufficiently large sample in each of the distinct populations collected in the Kuiper Belt to be able to measure, with statistical significance, how the fraction of binaries varies as a function of their particular dynamical paths into the Kuiper Belt. Today’s Kuiper Belt bears the imprints of the final stages of giant-planet building and migration; binaries may offer some of the best preserved evidence of that long-ago era.


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 10813

MgII Absorption Line Systems: Galaxy Halos or the Metal-Enriched IGM?

MgII QSO absorption lines detected in the spectra of background QSOs were used over a decade ago to infer that all redshift z > 0.2 galaxies have gaseous halos of radius ~ 60 kpc. The actual size of the halo was believed to be proportional to the luminosity of the galaxy. However, these conclusions are now much harder to understand in light of the results from numerical simulations which show how gas evolves in the universe. These models predict that gas and galaxies merely share the same filamentary structures defined by dark matter. If these models are correct, how are MgII systems and galaxies really related? We can better understand the distribution of absorbing gas if we FIRST select galaxies close to QSO sightlines and THEN search for MgII absorption at the redshift of the intervening galaxies. This is the antithesis of the original experiments which sought to find absorbing galaxies based on known MgII systems. The frequency with which we detect MgII lines from randomly selected galaxies should enable us to better understand if absorption arises in the halos of individual galaxies, or if MgII merely arises in the same IGM that galaxies inhabit. We have used ground-based telescopes to indentify twenty z = 0.31-0.55 galaxies within 14-51 kpc of a g < 20 QSO, and to search for MgII absorption at the galaxies' redshifts. Surprisingly, we find that only 50% of our QSOs show MgII absorption. In this proposal, we seek multi-color ACS images of twelve of the fields to i} correlate the incidence of MgII with galaxy morphology; ii} determine if absorption {or lack thereof} is related to galaxy disks or halos; iii} search for signs of galaxy interactions which may explain the large cross-sections of MgII systems; and iv} look for faint interloping galaxies closer to the line of sight than the one we identified. An important component of the program is to observe each field in the SDSS g-, r- and i-bands, to permit an estimate of the photometric redshift of any objects which lie closer to the QSO sightline than the identified galaxy, and which might actually be responsible for the absorption.

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/NIC2/NIC3 8793

NICMOS Post-SAA calibration – CR Persistence Part 4

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, ACS/WFC 10802

SHOES-Supernovae, HO, for the Equation of State of Dark energy

The present uncertainty in the value of the Hubble constant {resulting in an uncertainty in Omega_M} and the paucity of Type Ia supernovae at redshifts exceeding 1 are now the leading obstacles to determining the nature of dark energy. We propose a single, integrated set of observations for Cycle 15 that will provide a 40% improvement in constraints on dark energy. This program will observe known Cepheids in six reliable hosts of Type Ia supernovae with NICMOS, reducing the uncertainty in H_0 by a factor of two because of the smaller dispersion along the instability strip, the diminished extinction, and the weaker metallicity dependence in the infrared. In parallel with ACS, at the same time the NICMOS observations are underway, we will discover and follow a sample of Type Ia supernovae at z > 1. Together, these measurements, along with prior constraints from WMAP, will provide a great improvement in HST’s ability to distinguish between a static, cosmological constant and dynamical dark energy. The Hubble Space Telescope is the only instrument in the world that can make these IR measurements of Cepheids beyond the Local Group, and it is the only telescope in the world that can be used to find and follow supernovae at z > 1. Our program exploits both of these unique capabilities of HST to learn more about one of the greatest mysteries in science.


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




                          SCHEDULED      SUCCESSFUL 
FGS GSacq                07                     07 
FGS REacq                04                     04 
OBAD with Maneuver   24                     24 


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