NASA Hubble Space Telescope Daily Report # 3389 (part 1)
HUBBLE SPACE TELESCOPE
DAILY REPORT # 3389
PERIOD COVERED: DOYs 171-173
OBSERVATIONS SCHEDULED
ACS 9472
A Snapshot Survey for Gravitational Lenses among z >= 4.0 Quasars
Over the last few years, the Sloan Digital Sky Survey has revolutionized the study of high-redshift quasars by discovering over 200 objects with redshift greater than 4.0, more than doubling the number known in this redshift interval. The sample includes eight of the ten highest redshift quasars known. We propose a snapshot imaging survey of a well-defined sample of 250 z > 4.0 quasars in order to find objects which are gravitationally lensed. Lensing models including magnification bias predict that at least 4% of quasars in a flux-limited sample at z > 4 will be multiply lensed. Therefore this survey should find of order 10 lensed quasars at high redshift; only one gravitationally lensed quasar is currently known at z > 4. This survey will provide by far the best sample to date of high-redshift gravitational lenses. The observed fraction of lenses can put strong constraints on cosmological models, in particular on the cosmological constant Lambda. In addition, magnification bias can significantly bias estimates of the luminosity function of quasars and the evolution thereof; this work will constrain how important an effect this is, and thereby give us a better understanding of the evolution of quasars and black holes at early epochs, as well as constrain models for black hole formation.
ACS 9658
ACS Earth Flats
This program will obtain sequences of flat field images by observing the bright Earth. Several UV filters from the interim calibration program {9564} require additional exposures to obtain the required illumination. A few UV filters from this program will be repeated to monitor for changes in the flat fields and to verify the interim results. Since no streaks are observed in the UV, the wavelength coverage is extended to longer wavelengths in order to explore the severity of streaks in the flats from clouds in the FOV. We have added exposures for the HRC in the visible filters to verify the results derived from the L-flat campaign and to explore the severity of streaks. We have also added exposures on WFC using the minimum exposure time and using filters which will not saturate the brightest WFC pixel by more than 10 times the full well.
ACS 9482
ACS Pure Parallel Lyman-Alpha Emission Survey {APPLES}
Ly-alpha line emission is an efficient tool for identifying young galaxies at high redshift, because it is strong in galaxies with young stars and little or no dust — properties expected in galaxies undergoing their first burst of star- formation. Slitless spectroscopy with the ACS Wide-Field Camera and G800L grism allows an unmatched search efficiency for such objects over the uninterrupted range 4 <~ z <~ 7. We propose the ACS Pure Parallel Ly-alpha Emission Survey {“APPLES”}, to exploit this unique HST capability and so obtain the largest and most uniform sample of high redshift Ly-alpha emitters yet. Parallel observations will allow this survey to be conducted with minimal impact on HST resources, and we will place reduced images and extracted spectra in the public domain within three months of observation. We aim to find ~ 1000 Ly-alpha emitters, 5 times the biggest current sample of Ly-alpha emitters. This unprecedented sample will provide robust statistics on the populations and evolution of Ly-alpha emitters between redshifts 4–7; a robust measurement of the reionization redshift completely independent of the Gunn-Peterson trough; spatial clustering information for Ly-alpha emitters which would let us probe their bias function and hence halo mass as a function of redshift; many galaxies at redshift exceeding 6; and lower redshift serendipitous discoveries.
ACS 9463
Are OH/IR stars the youngest post-AGB stars? An ACS SNAPshot imaging survey
Essentially all well-characterized preplanetary nebulae {PPNs}– objects in transition between the AGB and planetary nebula evolutionary phases – are bipolar, whereas the mass-loss envelopes of AGB stars are strikingly spherical. In order to understand the processes leading to bipolar mass-ejection, we need to know at what stage of stellar evolution does bipolarity in the mass-loss first manifest itself? We have recently hypothesized that most OH/IR stars {evolved mass- losing stars with OH maser emission} are very young PPNe. We propose an ACS/SNAPshot imaging survey of a large, morphologically unbiased sample of these objects, selected using their IRAS 12-to-25micron colors. Our ground-based imaging study of OH/IR stars has revealed a few compact bipolar objects, supporting our hypothesis. However since most objects remain unresolved, HST observations are needed to determine how and when the bipolar geometry asserts itself. Our complementary program of interferometric mapping of the OH maser emission in our sources is yielding kinematic information with spatial resolution comparable to that in the HST images. The HST/radio data will provide crucial input for theories of post-AGB stellar evolution. In addition, these data will also indicate whether the multiple concentric rings, “searchlight beams”, and truncated equatorial disks recently discovered with HST in a few PPNs, are common or rare phenomena.
ACS 9674
CCD Daily Monitor
This program consists of basic tests to monitor, the read noise, the development of hot pixels and test for any source of noise in ACS CCD detectors. This programme will be executed once a day for the entire lifetime of ACS.
ACS 9650
CCD Hot Pixel Annealing
Hot pixel annealing will be performed once every 4 weeks. The CCD TECs will be turned off and heaters will be activated to bring the WFC detector temperature to about +10C. The HRC temperature will reach about 30C.This state will be held for approximately 24 hours, after which the heaters are turned off, the TECs turned on, and the CCDs returned to normal operating condition. To assess the effectiveness of this procedure, a bias and two dark images will be taken before and after the annealing procedure for both WFC and HRC.
ACS 9480
Cosmic Shear With ACS Pure Parallels
Small distortions in the shapes of background galaxies by foreground mass provide a powerful method of directly measuring the amount and distribution of dark matter. Several groups have recently detected this weak lensing by large-scale structure, also called cosmic shear. The high resolution and sensitivity of HST/ACS provide a unique opportunity to measure cosmic shear accurately on small scales. Using 260 parallel orbits in Sloan textiti {F775W} we will measure for the first time: beginlistosetlength sep0cm setlengthemsep0cm setlength opsep0cm em the cosmic shear variance on scales <0.7 arcmin, em the skewness of the shear distribution, and em the magnification effect. endlist Our measurements will determine the amplitude of the mass power spectrum sigma_8Omega_m^0.5, with signal-to-noise {s/n} ~ 20, and the mass density Omega_m with s/n=4. They will be done at small angular scales where non-linear effects dominate the power spectrum, providing a test of the gravitational instability paradigm for structure formation. Measurements on these scales are not possible from the ground, because of the systematic effects induced by PSF smearing from seeing. Having many independent lines of sight reduces the uncertainty due to cosmic variance, making parallel observations ideal.
ACS 9984
Cosmic Shear With ACS Pure Parallels
Small distortions in the shapes of background galaxies by foreground mass provide a powerful method of directly measuring the amount and distribution of dark matter. Several groups have recently detected this weak lensing by large-scale structure, also called cosmic shear. The high resolution and sensitivity of HST/ACS provide a unique opportunity to measure cosmic shear accurately on small scales. Using 260 parallel orbits in Sloan textiti {F775W} we will measure for the first time: beginlistosetlength sep0cm setlengthemsep0cm setlength opsep0cm em the cosmic shear variance on scales <0.7 arcmin, em the skewness of the shear distribution, and em the magnification effect. endlist Our measurements will determine the amplitude of the mass power spectrum sigma_8Omega_m^0.5, with signal-to-noise {s/n} ~ 20, and the mass density Omega_m with s/n=4. They will be done at small angular scales where non-linear effects dominate the power spectrum, providing a test of the gravitational instability paradigm for structure formation. Measurements on these scales are not possible from the ground, because of the systematic effects induced by PSF smearing from seeing. Having many independent lines of sight reduces the uncertainty due to cosmic variance, making parallel observations ideal.
ACS 9420
Intensive Coverage of the Eta Carinae Event in 2003
For a variety of reasons, HST can provide a very special and unique data set when Eta Car experiences its next spectroscopic event in mid-2003. Explaining the phenomenon is only part of the motivation. This star and its ejecta have unique characteristics that make them important for several branches of astrophysics; and when a spectroscopic event occurs, it’s like varying the parameters in an experiment {or rather, set of experiments}. The 2003 event will be the last chance in the forseeable future to obtain such a data set. Eta Carinae has extreme parameters; it is mysterious in surprisingly basic ways; and HST/STIS can gather useful data on it at a terrific rate. As we explain below, the proposed data set will be valuable in several independent ways: It will help solve a specific set of current problems, it will constitute a large and unique archival data base for both stellar and nebular astrophysics, and it will be well-suited for educational uses.
