Status Report

NASA Hubble Space Telescope Daily Report #5079

By SpaceRef Editor
April 26, 2010
Filed under , ,


Continuing to Collect World Class Science

PERIOD COVERED: 5am April 20 – 5am April 21, 2010 (DOY 110/09:00z-111/09:00z)



COS and WFC3 Observations of I Zwicky 18

We will take advantage of COS’ high sensitivity to study both the stellar and gaseous component (especially HeII 1640 and CIII] 1909), in I Zwicky 18 (IZw18). We will also take advantage of WFC3’s high-QE IR detector to obtain H-band images of IZw18. The new NIR images will used in combination with the archival V and I ACS/WFC data to better characterize the old stellar population, i.e. red giant branch and asymptotic giant branch stars. The WFC3 observations will be executed at carefully planned intervals to have a fair sampling in the H band of the light curve of the Cepheid variable stars already identified in IZw18.

COS/NUV 11900

NUV Internal/External Wavelength Scale Monitor

This program monitors the offsets between the wavelength scale set by the internal wavecal versus that defined by absorption lines in external targets. This is accomplished by observing two external radial velocity standard targets: HD187691 with G225M and G285M and HD6655 with G285M and G230L. The two standard targets have little flux in the wavelength range covered by G185M and so Feige 48 (sdO) is observed with this grating. Both Feige 48 and HD6655 are also observed in SMOV. The cenwaves observed in this program are a subset of the ones used during Cycle 17. Observing all cenwaves would require a considerably larger number of orbits. Constraints on scheduling of each target are placed so that each target is observed once every ~2-3 months. Observing the three targets every month would also require a considerably larger number of orbits.

STIS/CC 11845

CCD Dark Monitor Part 2

Monitor the darks for the STIS CCD.

STIS/CC 11847

CCD Bias Monitor-Part 2

Monitor the bias in the 1×1, 1×2, 2×1, and 2×2 bin settings at gain=1, and 1×1 at gain = 4, to build up high-S/N superbiases and track the evolution of hot columns.

STIS/CCD 11849

STIS CCD Hot Pixel Annealing

This purpose of this activity is to repair radiation induced hot pixel damage to the STIS CCD by warming the CCD to the ambient instrument temperature and annealing radiation-damaged pixels.

Radiation damage creates hot pixels in the STIS CCD Detector. Many of these hot pixels can be repaired by warming the CCD from its normal operating temperature near -83 deg. C to the ambient instrument temperature (~ +5 deg. C) for several hours. The number of hot pixels repaired is a function of annealing temperature. The effectiveness of the CCD hot pixel annealing process is assessed by measuring the dark current behavior before and after annealing and by searching for any window contamination effects.

WFC3/ACS/IR 11597

Spectroscopy of IR-Selected Galaxy Clusters at 1 < z < 1.5 We propose to obtain WFC3 G141 and G102 slitless spectroscopy of galaxy clusters at 1 < z < 1.5 that were selected from the IRAC survey of the Bootes NDWFS field. Our IRAC survey contains the largest sample of spectroscopically confirmed clusters at z > 1. The WFC3 grism data will measure H-alpha to determine SFR, and fit models to the low resolution continua to determine stellar population histories for the brighter cluster members, and redshifts for the red galaxies too faint for ground-based optical spectroscopy.

WFC3/ACS/IR 11600

Star Formation, Extinction, and Metallicity at 0.7< z<1.5: H-Alpha Fluxes and Sizes from a Grism Survey of GOODS-N The global star formation rate (SFR) is ~10x higher at z=1 than today. This could be due to drastically elevated SFR in some fraction of galaxies, such as mergers with central bursts, or a higher SFR across the board. Either means that the conditions in z=1 star forming galaxies could be quite different from local objects. The next step beyond measuring the global SFR is to determine the dependence of SFR, obscuration, metallicity, and size of the star-forming region on galaxy mass and redshift. However, SFR indicators at z=1 typically apply local calibrations for UV, [O II] and far-IR, and do not agree with each other on a galaxy-by-galaxy basis. Extinction, metallicity, and dust properties cause uncontrolled offsets in SFR calibrations. The great missing link is Balmer H-alpha, the most sensitive probe of SFR. We propose a slitless WFC3/G141 IR grism survey of GOODS-N, at 2 orbits/pointing. It will detect Ha+[N II] emission from 0.7< z<1.5, to L(Ha) = 1.7 x 10^41 erg/sec at z=1, measuring H-alpha fluxes and sizes for > 600 galaxies, and a small number of higher-redshift emitters. This will produce: an emission-line redshift survey unbiased by magnitude and color selection; star formation rates as a function of galaxy properties, e.g. stellar mass and morphology/mergers measured by ACS; comparisons of SFRs from H-alpha to UV and far-IR indicators; calibrations of line ratios of H-alpha to important nebular lines such as [O II] and H-beta, measuring variations in metallicity and extinction and their effect on SFR estimates; and the first measurement of scale lengths of the H-alpha emitting, star- forming region in a large sample of z~1 sources.

WFC3/ACS/IR 11731

Studying Cepheid Systematics in M81: H-Band Observations

The local value of the Hubble Constant remains one of the most important constraints in cosmology, but improving on the 10% accuracy of the HST Key Project is challenging. No improvements will be convincing until the metallicity dependence is well constrained and blending effects are fully understood. M81 and its dwarf companion Holmberg IX are superb laboratories for studying Cepheid systematics because they contain large numbers of bright Cepheids with a good spread in metallicity lying at a common, relatively close distance. We have identified 180 12< P< 70 day Cepheids in these two galaxies using the Large Binocular Telescope (compared to 30 in total by the KP), and will expand the sample further in 2008-2009. We will use 10 orbits with WFC3/IR to obtain H-band images of 100 Cepheids in M81 to add to the ACS/BVI calibrations we will obtain from archival data and 1 orbit with WFC3/UVIS to add B-band data for Holmberg IX. Four band BVIH photometry will allow us to flux calibrate, estimate extinction, measure metallicity effects and then check the results in detail. We can also examine blending effects on WFC3/IR data in a relatively nearby galaxy before it is applied to more distant galaxies. Our M81 sample is three times larger than the next best sample, that of NGC4258, and suffers less from blending because M81 is at half the distance, so it is an excellent laboratory for studying Cepheid systematics even if it lacks as precise a geometric distance as NGC4258. WFC3/ACS/UVIS/COS/NUV/STIS/CCD 11878 HST Post-SM4 and Cycle 17 Focal Plane Calibration This proposal will determine and monitor the SI positions and orientations in V2, V3 space. Accuracy goals are < 50 mas for position and between 0.04 and 0.01 degrees for angle (depending on SI). An astrometric open cluster (M35) is observed using guidestars with positions determined to ~ 20 mas. One or more astrometric targets are placed in the available SIs' major channels and POS TARGs can be used if necessary to step the target(s) over a significant fraction of the detector. This proposal will serve to update the SI positions and angles in the SIAF operational database. WFC3/IR 11719 A Calibration Database for Stellar Models of Asymptotic Giant Branch Stars Studies of galaxy formation and evolution rely increasingly on the interpretation and modeling of near-infrared observations. At these wavelengths, the brightest stars are intermediate mass asymptotic giant branch (AGB) stars. These stars can contribute nearly 50% of the integrated luminosity at near infrared and even optical wavelengths, particularly for the younger stellar populations characteristic of high-redshift galaxies (z>1). AGB stars are also significant sources of dust and heavy elements. Accurate modeling of AGB stars is therefore of the utmost importance.

The primary limitation facing current models is the lack of useful calibration data. Current models are tuned to match the properties of the AGB population in the Magellanic Clouds, and thus have only been calibrated in a very narrow range of sub-solar metallicities. Preliminary observations already suggest that the models are overestimating AGB lifetimes by factors of 2-3 at lower metallicities. At higher (solar) metallicities, there are no appropriate observations for calibrating the models.

We propose a WFC3/IR SNAP survey of nearby galaxies to create a large database of AGB populations spanning the full range of metallicities and star formation histories. Because of their intrinsically red colors and dusty circumstellar envelopes, tracking the numbers and bolometric fluxes of AGB stars requires the NIR observations we propose here. The resulting observations of nearby galaxies with deep ACS imaging offer the opportunity to obtain large (100-1000’s) complete samples of AGB stars at a single distance, in systems with well-constrained star formation histories and metallicities.

WFC3/UVIS 11594

A WFC3 Grism Survey for Lyman Limit Absorption at z=2

We propose to conduct a spectroscopic survey of Lyman limit absorbers at redshifts 1.8 < z < 2.5, using WFC3 and the G280 grism. This proposal intends to complete an approved Cycle 15 SNAP program (10878), which was cut short due to the ACS failure. We have selected 64 quasars at 2.3 < z < 2.6 from the Sloan Digital Sky Survey Spectroscopic Quasar Sample, for which no BAL signature is found at the QSO redshift and no strong metal absorption lines are present at z > 2.3 along the lines of sight. The survey has three main

observational goals. First, we will determine the redshift frequency dn/dz of the LLS over the column density range 16.0 < log(NHI) < 20.3 cm^-2. Second, we will measure the column density frequency distribution f(N) for the partial Lyman limit systems (PLLS) over the column density range 16.0 < log(NHI) < 17.5 cm^-2. Third, we will identify those sightlines which could provide a measurement of the primordial D/H ratio. By carrying out this survey, we can also help place meaningful constraints on two key quantities of cosmological relevance. First, we will estimate the amount of metals in the LLS using the f(N), and ground based observations of metal line transitions. Second, by determining f(N) of the PLLS, we can constrain the amplitude of the ionizing UV background at z~2 to a greater precision. This survey is ideal for a snapshot observing program, because the on-object integration times are all well below 30 minutes, and follow-up observations from the ground require minimal telescope time due to the QSO sample being bright. WFC3/UVIS 11905 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). FLIGHT OPERATIONS SUMMARY: Significant Spacecraft Anomalies: (The following are preliminary reports of potential non-nominal performance that will be investigated.) HSTARS: (None) COMPLETED OPS REQUEST: (None) COMPLETED OPS NOTES: (None)

FGS GSAcq 7 7
FGS REAcq 10 10
OBAD with Maneuver 3 3


SpaceRef staff editor.