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Daily Report #5084
HUBBLE SPACE TELESCOPE - Continuing to Collect World Class Science
DAILY REPORT #5084 PERIOD COVERED: 5am April 27 - 5am April 28, 2010 (DOY 117/09:00z-118/09:00z) OBSERVATIONS SCHEDULED ACS/WFC/WFC3/UV 11578 The Extremely Metal-Poor BCD Galaxy DDO 68: a Young Galaxy in the Local Universe ? A long standing question in astrophysics is the existence of young galaxies, in which stars are now forming for the first time, in the nearby (i.e., present-day) universe. Such galaxies would be the local analogs of primordial galaxies observed at high redshift. The most promising candidates have long been the most metal-poor systems, including dwarf irregulars (dIrrs) and blue compact dwarfs (BCDs). However, in many dIrrs and BCDs studied with HST an old (1 Gyr) underlying stellar population, as traced by red giant branch (RGB) stars, has been unambiguously detected. Even in I Zw 18, which is the most-metal poor prototype of the class and long the most controversial case, our group has recently succeeded in detecting an RGB. Nonetheless, there remains the possibility that the star formation histories of BCDs/dIrrs vary from galaxy to galaxy, and that truly young galaxies do exist in the local universe. A new test of these issues has only recently become possible with the identification of DDO 68 as an extremely metal-poor galaxy with an oxygen abundance equal to that of I Zw 18 (12+(O/H)=7.21). This galaxy is about a factor of 2-3 closer than I Zw 18, which yields the opportunity to avoid the many ambiguities that have plagued studies of I Zw 18. Also, DDO 68 resides in a void, making it more likely that star formation has been suppressed for a very long time. We will observe DDO 68 with ACS/WFC in F606W and F814W, plus F658N (Halpha) to correct the broad F606W for gas contamination. We will use WFC3 in parallel with the same filters to study radial population gradients. Deep color-magnitude diagrams (CMDs) reaching the depth of one magnitude below the predicted RGB tip will be constructed and interpreted based on synthetic CMD fitting. These data will determine unambiguously whether DDO 68 has an underlying old (RGB) stellar population or is forming stars for the first time. Finding just a single nearby ``young'' galaxy would have profound cosmological implications. COS/NUV/FUV/WFC3/UVIS/IR 11533 COS-GTO: Accretion Flows and Winds of Pre-Main Sequence Stars COS will obtain spectra of T Tauri stars to study accretion flows and wind absorption features in ultraviolet emission lines. Observations of several T Tauri stars with different inclination angles with respect to the line of sight will determine the temperature distributions, flow velocities, and column densities of both inflows and outflows for these stars. 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 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. STIS/CCD 11852 STIS CCD Spectroscopic Flats C17 The purpose of this proposal is to obtain pixel-to-pixel lamp flat fields for the STIS CCD in spectroscopic mode. STIS/CCD/FGS 11848 CCD Read Noise Monitor This proposal measures the read noise of all the amplifiers (A, B, C, D) on the STIS CCD using pairs of bias frames. Full-frame and binned observations are made in both Gain 1 and Gain 4, with binning factors of 1x1, 1x2, 2x1, and 2x2. All exposures are internals. Pairs of visits are scheduled monthly for the first four months and then bi-monthly after that. 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/IR 11936 IR Grism Flux Calibration This program will determine image displacement, spectral trace and flux calibration for the IR G102 and G141 grisms as a function of spatial position within the field of view. The HST flux standard GD71 will be observed in a 9-point pattern in the IR field of view, which will provide the necessary image displacement, spectral trace, and throughput measurements. WFC3/IR/S/C 11929 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/UV/ACS/WFC 11636 First Resolved Imaging of Escaping Lyman Continuum The emission from star-forming galaxies appears to be responsible for reionization of the universe at z 6. However, the models that attempt to describe the detailed impact of high-redshift galaxies on the surrounding inter-galactic medium (IGM) are strongly dependent upon several uncertain parameters. Perhaps the most uncertain is the fraction of HI-ionizing photons produced by young stars that escape into the IGM. Most attempts to measure this "escape fraction" have produced null results. Recently, a small subset of z~3 Lyman Break Galaxies (LBGs) has been found exhibiting large escape fractions. It remains unclear however, what differentiates them from other LBGs. Several models attempt to explain how such a large fraction of ionizing continuum can escape through the HI and dust in the ISM (eg. "chimneys" created by SNe winds, globular cluster formation, etc.), each producing unique signatures which can be observed with resolved imaging of the escaping Lyman continuum. To date, there are only six LBGs with individual detections of escaping Lyman continuum at any redshift. We propose a single deep, high resolution WFC3/UVIS image of the ionizing continuum (F336W) and the rest-frame UV/optical (F606W/F814W/F160W) of five of these six LBGs with large escape fractions. These LBGs have a high surface density and large escape fractions, and lie at the optimal redshift for Lyman continuum imaging with UVIS filters, making our sample especially suitable for follow-up. With these data we will discern the mechanisms responsible for producing large escape fractions, and therefore gain insight into the process of reionization. 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). WFC3/UVI 11911 UVIS L-Flats and Geometric Distortion Multiple pointing observations of the globular cluster Omega Centauri (NGC 5139) will be used to measure the filter-dependent low frequency flat field (L-flat) corrections and stability for a key set of 10 broadband filters used by GO programs. The selected filters are F225W, F275W, F336W, F390W, F438W, F555W, F606W, F775W, F814W and F850LP. By measuring relative changes in brightness of a star over different portions of the detector, we will determine local variations in the UVIS detector response. The broad wavelength range covered by these observations will allow us to derive the L-flat correction for the remaining wide, medium and narrow-band UVIS filters. The same data will also be used to determin and correct the geometric distotrion that affects UVIS data. The broad wavelength range covered by these observations will allow us to measure the geometric distortion dependence with wavelength and filters and to provide the most appropriate correction over the entire wavelength range provided by UVIS. ACS/WFC 11995 CCD Daily Monitor (Part 2) 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 320 orbits (20 weeks) from 1 February 2010 to 20 June 2010. FLIGHT OPERATIONS SUMMARY: Significant Spacecraft Anomalies: (The following are preliminary reports of potential non-nominal performance that will be investigated.) HSTARS: 12255 - Following successful GSAcq(2,3,3), a Loss of Lock occurred while guiding with FGS-2, and FGS-3 at 188/04:27:02z. Subsequent REAcqs(2,3,3) were successful. Observations possibly affected. WFC3 47 Proposal ID#11911, ACS #85, Proposal ID#11995. COMPLETED OPS REQUEST: (None) COMPLETED OPS NOTES: (None) SCHEDULED SUCCESSFUL FAILURE TIMES FGS GSAcq 06 06 FGS REAcq 10 10 OBAD with Maneuver 03 03 LOSS of LOCK 118/04:29:57z SIGNIFICANT EVENTS: (None) |
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