HUBBLE SPACE TELESCOPE - Continuing to Collect World Class Science
DAILY REPORT #5180
PERIOD COVERED: 5am September 13 - 5am September 14, 2010 (DOY 256/09:00z-257/09:00z)
FLIGHT OPERATIONS SUMMARY:
Significant Spacecraft Anomalies: (The following are preliminary reports of potential non-nominal performance that will be investigated.)
12402 - COS 1021 STB Message received at 257/01:22z, following successful GSAcq (2,1,1) at 257/01:15:46z, indicating take data flag was down when a target acquisition macro was about to make a slew request.
This program comprises basic tests for measuring the read noise and dark current of the ACS WFC and for tracking the growth of hot pixels. The recorded frames are used to create bias and dark reference images for science data reduction and calibration. This program will be executed four days per week (Mon, Wed, Fri, Sun) for the duration of Cycle 17. To facilitate scheduling, this program is split into three proposals. This proposal covers 308 orbits (19.25 weeks) from 21 June 2010 to 1 November 2010.
SLACS for the Masses: Extending Strong Lensing to Lower Masses and Smaller Radii
Strong gravitational lensing provides the most accurate possible measurement of mass in the central regions of early-type galaxies (ETGs). We propose to continue the highly productive Sloan Lens ACS (SLACS) Survey for strong gravitational lens galaxies by observing a substantial fraction of 135 new ETG gravitational-lens candidates with HST-ACS WFC F814W Snapshot imaging. The proposed target sample has been selected from the seventh and final data release of the Sloan Digital Sky Survey, and is designed to complement the distribution of previously confirmed SLACS lenses in lens-galaxy mass and in the ratio of Einstein radius to optical half-light radius. The observations we propose will lead to a combined SLACS sample covering nearly two decades in mass, with dense mapping of enclosed mass as a function of radius out to the half-light radius and beyond. With this longer mass baseline, we will extend our lensing and dynamical analysis of the mass structure and scaling relations of ETGs to galaxies of significantly lower mass, and directly test for a transition in structural and dark-matter content trends at intermediate galaxy mass. The broader mass coverage will also enable us to make a direct connection to the structure of well-studied nearby ETGs as deduced from dynamical modeling of their line-of-sight velocity distribution fields. Finally, the combined sample will allow a more conclusive test of the current SLACS result that the intrinsic scatter in ETG mass-density structure is not significantly correlated with any other galaxy observables. The final SLACS sample at the conclusion of this program will comprise approximately 130 lenses with known foreground and background redshifts, and is likely to be the largest confirmed sample of strong-lens galaxies for many years to come.
SWELLS: Doubling the Number of Disk-dominated Edge-on Spiral Lens Galaxies
The formation of realistic disk galaxies within the LCDM cosmology is still largely an unsolved problem. Theory is now beginning to make predictions for how dark matter halos respond to galaxy formation, and for the properties of disk galaxies. Measuring the density profiles of dark matter halos on galaxy scales is therefore a strong test for the standard paradigm of galaxy formation, offering great potential for discovery. However, the degeneracy between the stellar and dark matter contributions to galaxy rotation curves remains a major obstacle. Strong gravitational lensing, when combined with spatially resolved kinematics and stellar population models, can solve this long-standing problem. Unfortunately, this joint methodology could not be exploited until recently due to the paucity of known edge-on spiral lenses. We have developed and demonstrated an efficient technique to find exactly these systems. During supplemental cycle-16 we discovered five new spiral lens galaxies, suitable for rotation curve measurements. We propose multi-color HST imaging of 16 candidates and 2 partially-imaged confirmed systems, to measure a sample of eight new edge-on spiral lenses. This program will at least double the number of known disk-dominated systems. This is crucial for constraining the relative contribution of the disk, bulge and dark halo to the total density profile.
The Hosts of High Redshift Gamma-Ray Bursts
Gamma-ray bursts are the most luminous explosive events known, acting as beacons to the high redshift universe. Long duration GRBs have their origin in the collapse of massive stars and thus select star forming galaxies across a wide range of redshift. Due to their bright afterglows we can study the details of GRB host galaxies via absorption spectroscopy, providing redshifts, column densities and metallicities for galaxies far too faint to be accessible directly with current technology. We have already obtained deep ground based observations for many hosts and here propose ACS/WFC3 and WFC3 observations of the fields of bursts at z>3 which are undetected in deep ground based images. These observations will study the hosts in emission, providing luminosities and morphologies and will enable the construction of a sample of high-z galaxies with more detailed physical properties than has ever been possible before.
CCD Dark Monitor Part 2
Monitor the darks for the STIS CCD.
CCD Bias Monitor-Part 2
Monitor the bias in the 1x1, 1x2, 2x1, and 2x2 bin settings at gain=1, and 1x1 at gain = 4, to build up high-S/N superbiases and track the evolution of hot columns.
Cosmo-chronometry and Elemental Abundance Distribution of the Ancient Star HE1523-0901
We propose to obtain near-UV HST/STIS spectroscopy of the extremely metal-poor, highly r-process-enhanced halo star HE 1523-0901, in order to produce the most complete abundance distribution of the heaviest stable elements, including platinum, osmium, and lead. These HST abundance data will then be used to estimate the initial abundances of the long-lived radioactive elements thorium and uranium, and by comparison with their observed abundances, enable an accurate age determination of this ancient star. The use of radioactive chronometers in stars provides an independent lower limit on the age of the Galaxy, which can be compared with alternative limits set by globular clusters and by analysis from WMAP. Our proposed observations of HE1523-0901 will also provide significant new information about the early chemical history of the Galaxy, specifically, the nature of the first generations of stars and the types of nucleosynthetic processes that occurred at the onset of Galactic chemical evolution.
The Distance Dependence of the Interstellar N/O Abundance Ratio: A Gould Belt Influence?
The degree of elemental abundance homogeneity in the interstellar medium is a function of the enrichment and mixing processes that govern galactic chemical evolution. Observations of young stars and the interstellar gas within ~500 pc of the Sun have revealed a local ISM that is so well-mixed it is having an impact on ideas regarding the formation of extrasolar planets. However, the situation just beyond the local ISM is not so clear. Sensitive UV absorption line measurements have recently revealed a pattern of inhomogeneities in the interstellar O, N, and Kr gas-phase abundances at distances of ~500 pc and beyond that appear nucleosynthetic in origin rather than due to dust depletion. In particular, based on a sample of 13 sightlines, Knauth et al. (2006) have found that the nearby stars (d < 500 pc) exhibit a mean interstellar N/O abundance ratio that is significantly higher (0.18 dex) than that toward the more distant stars. Interestingly, all of their sightlines lie in the sky vicinity of the Gould Belt of OB associations, molecular clouds, and diffuse gas encircling the Sun at a distance of ~400 pc. Is it possible that mixing processes have not yet smoothed out the recent ISM enrichment by massive stars in the young Belt region? By measuring the interstellar N/O ratios in a strategic new sample of sightlines with STIS, we propose to test the apparent N/O homogeneity inside the Gould Belt and determine if the apparent decline in the N/O ratio with distance is robust and associated with the Belt region.
STIS Cycle 17 MAMA Dark Monitor
This proposal monitors the behavior of the dark current in each of the MAMA detectors.
The basic monitor takes two 1380s ACCUM darks each week with each detector. However, starting Oct 5, pairs are only included for weeks that the LRP has external MAMA observations planned. The weekly pairs of exposures for each detector are linked so that they are taken at opposite ends of the same SAA free interval. This pairing of exposures will make it easier to separate long and short term temporal variability from temperature dependent changes.
For both detectors, additional blocks of exposures are taken once every six months. These are groups of five 1314s FUV-MAMA Time-Tag darks or five 3x315s NUV ACCUM darks distributed over a single SAA-free interval. This will give more information on the brightness of the FUV MAMA dark current as a function of the amount of time that the HV has been on, and for the NUV MAMA will give a better measure of the short term temperature dependence.
Determining the Physical Nature of a Unique Giant Lya Emitter at z=6.595
We propose deep WFC3/IR imaging for a giant Lya emitter (LAE) with a Keck spectroscopic redshift of z=6.595 discovered by extensive narrow-band imaging with Subaru in the SXDS-UKIDSS/UDS field. This remarkable object is unique in many respects including its large stellar mass and luminous nebula which extends over 17 kpc; no equivalent source has been found in other surveys. The nature of this rare object is unclear. Fundamental to progress is determining the origin of star formation in such an early massive object; if the age of the stellar population is short we are likely witnessing a special moment in the formation history of a massive galaxy. The heating source for the nebula is also unclear; options include intense star formation, the infall of cold gas onto a dark halo or shock heating from a merger. We will take deep broad-band (F125W and F160W) images and an intermediate-band (F098M) image which will be analyzed in conjunction with ultra-deep IRAC 3.6 and 4.5 micron data being taken by the Spitzer/SEDS project. These data will enable us to constrain the star formation rate and stellar age. Moreover, the UV continuum morphology and Lya-line distribution will be investigated for evidence of a major merger, cold accretion, or hot bubbles associated with outflows. We will address the physical origin of the remarkable object observed at an epoch where massive galaxies are thought to begin their assembly.
IR Dark Current Monitor
Analyses of ground test data showed that dark current signals are more reliably removed from science data using darks taken with the same exposure sequences as the science data, than with a single dark current image scaled by desired exposure time. Therefore, dark current images must be collected using all sample sequences that will be used in science observations. These observations will be used to monitor changes in the dark current of the WFC3-IR channel on a day-to-day basis, and to build calibration dark current ramps for each of the sample sequences to be used by Gos in Cycle 17. For each sample sequence/array size combination, a median ramp will be created and delivered to the calibration database system (CDBS).
WFC3 UVIS CCD Daily Monitor
The behavior of the WFC3 UVIS CCD will be monitored daily with a set of full-frame, four-amp bias and dark frames. A smaller set of 2Kx4K subarray biases are acquired at less frequent intervals throughout the cycle to support subarray science observations. The internals from this proposal, along with those from the anneal procedure (Proposal 11909), will be used to generate the necessary superbias and superdark reference files for the calibration pipeline (CDBS).
UVIS Earth Flats
This program is an experimental path finder for Cycle 18 calibration. Visible-wavelength flat fields will be obtained by observing the dark side of the Earth during periods of full moon illumination. The observations will consist of full-frame streaked WFC3 UVIS imagery: per 22- min total exposure time in a single "dark-sky" orbit, we anticipate collecting 7000 e/pix in F606W or 4500 e/pix in F814W. To achieve Poisson S/N > 100 per pixel, we require at least 2 orbits of F606W and 3 orbits of F814W.
For UVIS narrowband filters, exposures of 1 sec typically do not saturate on the sunlit Earth, so we will take sunlit Earth flats for three of the more-commonly used narrowband filters in Cycle 17 plus the also-popular long-wavelength quad filters, for which we get four filters at once.
Why not use the Sunlit Earth for the wideband visible-light filters? It is too bright in the visible for WFC3 UVIS minimum exposure time of 0.5 sec. Similarly, for NICMOS the sunlit-Earth is too bright which saturates the detector too quickly and/or induces abnormal behaviors such as super-shading (Gilmore 1998, NIC 098-011). In the narrowband visible and broadband near- UV is not too bright (predictions in Cox et al. 1987 "Standard Astronomical Sources for HST: 6. Spatially Flat Fields." and observations in ACS Program 10050).
Other possibilities? Cox et al.'s Section II.D addresses many other possible sources for flat fields, rejecting them for a variety of reasons. A remaining possibility would be the totally eclipsed moon. Such eclipses provide approximately 2 hours (1 HST orbit) of opportunity per year, so they are too rare to be generically useful. An advantage of the moon over the Earth is that the moon subtends less than 0.25 square degree, whereas the Earth subtends a steradian or more, so scattered light and light potentially leaking around the shutter presents additional problems for the Earth. Also, we're unsure if HST can point 180 deg from the Sun.
UVIS Hot Pixel Anneal
The on-orbit radiation environment of WFC3 will continually generate new hot pixels. This proposal performs the procedure required for repairing those hot pixels in the UVIS CCDs. During an anneal, the two-stage thermo-electric cooler (TEC) is turned off and the four-stage TEC is used as a heater to bring the UVIS CCDs up to ~20 deg. C. As a result of the CCD warmup, a majority of the hot pixels will be fixed; previous instruments such as WFPC2 and ACS have seen repair rates of about 80%. Internal UVIS exposures are taken before and after each anneal, to allow an assessment of the procedure's effectiveness in WFC3, provide a check of bias, global dark current, and hot pixel levels, as well as support hysteresis (bowtie) monitoring and CDBS reference file generation. One IR dark is taken after each anneal, to provide a check of the IR detector.