Status Report

NASA Hubble Space Telescope Daily Report #4072

By SpaceRef Editor
March 17, 2006
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NASA Hubble Space Telescope Daily Report #4072

HUBBLE SPACE TELESCOPE – Continuing to collect World Class Science


PERIOD COVERED: UT March 16, 2006 (DOY 075)


ACS/HRC 10556

Neutral Gas at Redshift z=0.5

Damped Lyman-alpha systems {DLAs} are used to track the bulk of the neutral hydrogen gas in the Universe. Prior to HST UV spectroscopy, they could only be studied from the ground at redshifts z>1.65. However, HST has now permitted us to discover 41 DLAs at z<1.65 in our previous surveys. Followup studies of these systems are providing a wealth of information about the evolution of the neutral gas phase component of the Universe. But one problem is that these 41 low-redshift systems are spread over a wide range of redshifts spanning nearly 70% of the age of the Universe. Consequently, past surveys for low-redshift DLAs have not been able to offer very good precision in any small redshift regime. Here we propose an ACS-HRC- PR200L spectroscopic survey in the redshift interval z=[0.37, 0.7] which we estimate will permit us to discover another 41 DLAs. This will not only allow us to double the number of low-redshift DLAs, but it will also provide a relatively high-precision regime in the low-redshift Universe that can be used to anchor evolutionary studies. Fortunately DLAs have high absorption equivalent width, so ACS-HRC-PR200L has high-enough resoultion to perform this proposed MgII-selected DLA survey.

ACS/HRC 10599

Multi-color imaging of two 1 Gyr old debris disks within 20 pc of the Sun: Astrophysical mirrors of our Kuiper

We report the first scattered light detections of two debris disk around an F star and a K star using optical coronagraphy and the Hubble Space Telescope. With ages ~1 Gyr, these are the oldest debris disks thus far seen in the optical. We propose deep, multi-roll angle coronagraphic imaging with HST ACS and NICMOS to confirm and characterize the disks in terms of structure and composition. The disks appear to have belt-like morphology that is consistent with the existence of planetary companions or other perturbing bodies. Since these disks are close to our Kuiper Belt in an evolutionary context, detailed understanding of their mass, structure and composition will provide a fresh perspective for inferring the history and properties of our own trans-Neptunian region.

ACS/SBC 10736

ACS UV contamination monitor

The observations consist of imaging and spectroscopy with SBC and HRC of the cluster NGC 6681 in order to monitor the temporal evolution of the UV sensitivity of the SBC and the HRC. All UV modes except for SBC PR130L will be used.

ACS/WFC 10496

Decelerating and Dustfree: Efficient Dark Energy Studies with Supernovae and Clusters

We propose a novel HST approach to obtain a dramatically more useful “dust free” Type Ia supernovae {SNe Ia} dataset than available with the previous GOODS searches. Moreover, this approach provides a strikingly more efficient search-and-follow-up that is primarily pre- scheduled. The resulting dark energy measurements do not share the major systematic uncertainty at these redshifts, that of the extinction correction with a prior. By targeting massive galaxy clusters at z > 1 we obtain a five-times higher efficiency in detection of Type Ia supernovae in ellipticals, providing a well-understood host galaxy environment. These same deep cluster images then also yield fundamental calibrations required for future weak lensing and Sunyaev-Zel’dovich measurements of dark energy, as well as an entire program of cluster studies. The data will make possible a factor of two improvement on supernova constraints on dark energy time variation, and much larger improvement in systematic uncertainty. They will provide both a cluster dataset and a SN Ia dataset that will be a longstanding scientific resource.

ACS/WFC 10524

Blue Stragglers: a key stellar population to probe internal cluster dynamics

This proposal is part of a coordinated project devoted to understand the interplay of globular cluster {GC} dynamics and the formation and evolution of blue straggler stars {BSS}. By using a combination of HST and ground-based observations we are constructing complete BSS surveys in a sample of GCs; complete BSS surveys require mid-UV HST observations in the center and wide field CCD ground based observations under excellent seeing conditions of the exterior. Up to now only four clusters have been surveyed in this way and the results are surprising: in three GCs {M3, 47 Tuc, NGC 6752} we have discovered that the BSS radial distribution is bimodal, highly peaked in the cluster center, rapidly decreasing at intermediate radii and rising again at large radii {Ferraro et al. 1997, 2004, Sabbi et al. 2004}, conversely BSS population in Omega Centauri does not show any signature of the segregation which would be expected for a class of objects arising from either stellar interactions or binarity {Ferraro et al. 2005}. These observational facts are opening a new prospective in the study of the formation processes and evolution of BSS in GCs. By using extensive simulations, we demonstrated that the spatial distribution of BSS observed in 47 Tuc can be only reproduced if a sizable fraction of BSS is generated {via mass transfer in primordial binaries} in the peripheral region of the cluster {Mapelli et al 2004}, thus excluding a purely collisional formation scenario. Here we propose mid-UV imaging of a few clusters suspected of harboring a large population of central BSS and a few known to have many BSS the external region. These are good candidates for determining accurate BSS radial distributions. The modest amount of time proposed here will go far to determine the ubiquity of BSS bimodality and to constrain models of dynamical evolution. Since we believe the proposed observations would be useful to the entire stellar community {for multifold purposes} we waive the propretary period.

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.

NICS3 10754

Spectrophotometric Standards for Cross-Observatory Calibration

This program will obtain NICMOS spectrophotometry of four main sequence A stars and four K giants, each selected from the Spitzer IRAC photometric calibration target and/or candidate calibration target lists. These observations will supplement existing HST observations of DA white dwarfs and solar analogs, and will provide a broad base of stellar types for spectrophotometric cross calibration of HST, Spitzer, and eventually JWST. The targets are chosen to be faint enough for unsaturated observations with JWST NIRSPEC, yet still bright enough for high signal to noise in relatively short observations with HST+NICMOS and with Spitzer+IRAC.


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


10172 – GSAcq(2,1,2) failed to RGA control (T2G) due to stop flag on FGS-1 @ 075/2205z

The GSAcq(2,1,2) scheduled at 075/22:05:53 – 22:13:58 failed to RGA control due to stop flag (QF1STOPF) on FGS-1. Pre-acquisition OBADs were successful. OBAD2 at 075/22:01:23 had total (RSS) attitude correction value of 15.12 arcseconds.



                           SCHEDULED      SUCCESSFUL      FAILURE TIMES
GSacq                 14                    13                  075/2205z 
(HSTAR 10172)
FGS REacq                 01                     01
OBAD with Maneuver   30                     30


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