Status Report

NASA Hubble Space Telescope Daily Report #4081

By SpaceRef Editor
March 30, 2006
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NASA Hubble Space Telescope Daily Report #4081

HUBBLE SPACE TELESCOPE – Continuing to collect World Class Science


PERIOD COVERED: UT March 29, 2006 (DOY 089)


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 CCDs daily monitor

This program consists of a set of basic tests to monitor, the read noise, the development of hot pixels and test for any source of noise in ACS CCD detectors. The files, biases and dark will be used to create reference files for science calibration. This programme will be for the entire lifetime of ACS. Changes from cycle 13:- The default gain for WFC is 2 e-/DN. As before bias frames will be collected for both gain 1 and gain 2. Dark frames are acquired using the default gain {2}. This program cover the period Oct, 2 2005- May, 29-2006. The second half of the program has a different proposal number: 10758.

ACS/WFC 10592

An ACS Survey of a Complete Sample of Luminous Infrared Galaxies in the Local Universe

At luminosities above 10^11.4 L_sun, the space density of far-infrared selected galaxies exceeds that of optically selected galaxies. These `luminous infrared galaxies’ {LIRGs} are primarily interacting or merging disk galaxies undergoing enhanced star formation and Active Galactic Nuclei {AGN} activity, possibly triggered as the objects transform into massive S0 and elliptical merger remnants. We propose ACS/WFC imaging of a complete sample of 88 L_IR > 10^11.4 L_sun luminous infrared galaxies in the IRAS Revised Bright Galaxy Sample {RBGS: i.e., 60 micron flux density > 5.24 Jy}. This sample is ideal not only in its completeness and sample size, but also in the proximity and brightness of the galaxies. The superb sensitivity, resolution, and field of view of ACS/WFC on HST enables a unique opportunity to study the detailed structure of galaxies that sample all stages of the merger process. Imaging will be done with the F439W and F814W filters {B and I-band} to examine as a function of both luminosity and merger state {i} the evidence at optical wavelengths of star formation and AGN activity and the manner in which instabilities {bars and bridges} in the galaxies may funnel material to these active regions, {ii} the relationship between star formation and AGN activity, and {iii} the structural properties {AGN, bulge, and disk components} and fundamental parameters {effective radius and surface brightness} of LIRGs and their similarity with putative evolutionary byproducts {elliptical, S0 and classical AGN host galaxies}. This HST survey will also bridge the wavelength gap between a Spitzer imaging survey {covering seven bands in the 3.6-160 micron range} and a GALEX UV imaging survey of these galaxies, but will resolve complexes of star clusters and multiple nuclei at resolutions well beyond the capabilities of either Spitzer or GALEX. The combined datasets will result in the most comprehensive multiwavelength study of interacting and merging galaxies to date.

ACS/WFC 10605

Quantifying Star Formation and Feedback: The M81 Group Dwarf Galaxies

Studies of the impact of star formation via stellar winds and supernovae {‘feedback’} on the properties of a galaxy are of fundamental importance to understanding galaxy evolution. One crucial aspect in these studies is a precise census of the recent star formation in a galaxy. The aim of this proposal is to obtain spatially resolved star formation histories with a time resolution of roughly 30 Myr over the last 500 Myr in a carefully designed sample using the absolutely unique capabilities of the ACS. Our sample comprises 10 galaxies in the M81 group which is host to a wide diversity of dwarf star forming galaxies. They span ranges of 6 magnitudes in luminosity, 1000 in current star formation rate, and 0.5 dex in metallicity. The ACS observations will allow us to directly observe the strength and spatial relationships of all of the star formation in these galaxies in the last 500 Myr. We can then quantify the star formation and measure {1} the fraction of star formation that is triggered by feedback, {2} the fraction of star formation that occurs in clusters and associations, and {3} to what degree future star formation is governed by the feedback from previous star formation. The ACS observations will be complemented with high-quality ancillary data collected by our team for all galaxies {e.g., Spitzer, UV/optical/NIR, VLA HI}. We will calculate the energy created by star formation events and compare it to the estimated energy deposited into the local ISM. This will enable us to construct prescriptions of how star formation and feedback depend on metallicity, size, gas content, and current star formation rates in galaxies. Our resolved star formation maps will be compared with star formation rates inferred from H-alpha, UV, and IR observations – allowing an independent calibration of these techniques. Recent ACS imaging by us of one galaxy in the same group clearly demonstrates the feasibility of the proposed program. Most of the sample galaxies are located in the CVZ, making this an extremely efficient program.

ACS/WFC 10775

An ACS Survey of Galactic Globular Clusters

We propose to conduct an ACS/WFC imaging survey of Galactic globular clusters. We will construct the most extensive and deepest set of photometry and astrometry to-date for these systems reaching a main sequence mass of ~0.2 solar mass with S/N >= 10. We will combine these data with archival WFPC2 and STIS images to determine proper motions for the stars in our fields. The resultant cleaned cluster CMDs will allow us to study a variety of scientific questions. These include [but are not limited to] 1} the determination of cluster ages and distances 2} the construction of main sequence mass functions and the issue of mass segregation 3} the internal motions and dynamical evolution of globular clusters, and 4} absolute cluster motions, orbits, and the Milky Way gravitational potential. We anticipate that the unique resource provided by the proposed treasury archive will play a central role in the field of globular cluster studies for decades, with a stature comparable to that of the Hubble Deep Field for high redshift studies.


What Are Stalled Preplanetary Nebulae? An ACS SNAPshot Survey

Essentially all planetary nebulae {PNs} are aspherical, whereas the mass-loss envelopes of AGB stars are strikingly spherical. Our previous SNAPshot surveys of a morphologically unbiased sample of pre-planetary nebulae {PPNs} — objects in transition between the AGB and PN evolutionary phases — show that roughly half our observed targets are resolved, with bipolar or multipolar morphologies. Spectroscopic observations of our sample confirm that these objects have not yet evolved into planetary nebulae. Thus, the transformation from spherical to aspherical geometries has already fully developed by the time these dying stars have become PPNs. Although our current studies have yielded exciting results, they are limited in two important ways — {1} the number of well-resolved objects is still small {18}, and the variety of morphologies observed relatively multitudinous, hence no clear trends can yet be established between morphology and other source properties {e.g., near-IR, far-IR colors, stellar spectral type, envelope mass}, and {2} the current samples are strongly biased towards small PPNs, as inferred from their low 60-to-25 micron flux ratios [R{60/25}<1]. However, the prototype of objects with R{60/25}>1, the Frosty Leo Nebula, has a puzzlingly large post-AGB age {almost 10^4 yr} and a fairly cool central star, very different from the expectations of single-star stellar evolutionary models. A proposed, but still speculative, hypothesis for such objects is that the slow evolution of the central star is due to backflow of material onto the mass-losing star, retarding its evolution towards the PN phase. This hypothesis has significant consequences for both stellar and nebular evolution. We therefore propose a survey of PPNs with R{60/25}>1 which is heavily weighted towards the discovery of such “stalled PPNs”. Supporting kinematic observations using long-slit optical spectroscopy {with the Keck}, millimeter and radio interferometric observations {with OVRO, VLA & VLBA} are being undertaken. The results from this survey {together with our previous work} will allow us to draw general conclusions about the complex mass-outflow processes affecting late stellar evolution, and will provide crucial input for theories of post-AGB stellar evolution. Our survey will produce an archival legacy of long-standing value for future studies of dying stars.


HST/ACS Mosaic of M82

A six-pointing ACS WFC mosaic of the galaxy M82 will be obtained in four filters, B, V, I and H- alpha. Four orbits per pointing will allow high-quality S/N images of the entire galaxy.


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


10187 – GSAcq (1,2,1) resulted in fine lock backup due to scan step limit exceeded on FGS-1 088/20:08:44z

The GSAcq(1,2,1) scheduled at 088/20:04:59-20:12:06 resulted in finelock backup (2,0,2) using FGS-2, due to scan step limit exceeded on FGS-1. Pre-acquisition OBADs were successful. OBAD2 at 088/19:59:59 had total attitude correction (RSS) value of 13.41 arcseconds. OBAD MAP had total attitude correction (RSS) value of 7.06 arcseconds


17676-0 – Eclipse Management, GMT Day 88 @ 088/10:21:43z

17675-2 – Patch SOC1 and SOC2 Safing Limits for Solar Eclipse 2006/088 @ 088/10:33:51z

17677-0 – AGO GSTDN Engineering Test Supports @ 089/01:25z


                            SCHEDULED      SUCCESSFUL
FGS GSacq                 07                     07
FGS REacq                 08                     08
OBAD with Maneuver    26                     26


Eclipse Flash Report – 3/29/06

Two eclipse events occurred over the period of GMT 88/09:13 through 88/10:02. With the second eclipse occurring near middle of orbit day and having a peak darkness of ~92 percent darkness, ROP PS-02 was performed to minimize the impacts of this eclipse on the spacecraft. The steps to increase the CSS failure timer was completed prior to the first eclipse event at GMT 88/06:10. Additional steps were taken to lower the SOC 1 and SOC 2 safemode limits by 10 A-hrs to 171 A-hr and 111 A-hr, respectively. This recommendation was performed as a proactive measure. Resetting of these limits was completed by 88/10:32. ROP PS-02 was also completed by this time. Preliminary results from the second eclipse event showed that at the start of that orbit day the pressure-based SOC was 204 A-hr. After the eclipse, Benchmark Reset Threshold was achieved about 12 minutes prior to EON. The SOC reached 248 A-hr at EON (088/10:30).

SpaceRef staff editor.