Engineering topics

Kimble, R. A.

Publications and source records attributed to Kimble, R. A..

11 records

NASA NTRS2012

The Size Evolution of Passive Galaxies: Observations From the Wide-Field Camera 3 Early Release Science Program

We present the size evolution of passively evolving galaxies at z approximately 2 identified in Wide-Field Camera 3 imaging from the Early Release Science program. Our sample was constructed using an analog to the passive BzK galaxy selection criterion, which isolates galaxies with little or no ongoing star formation at z greater than approximately 1.5. We identify 30 galaxies in approximately 40 arcmin(sup 2) to H less than 25 mag. By fitting the 10-band Hubble Space Telescope photometry from 0.22 micrometers less than approximately lambda (sub obs) 1.6 micrometers with stellar population synthesis models, we simultaneously determine photometric redshift, stellar mass, and a bevy of other population parameters. Based on the six galaxies with published spectroscopic redshifts, we estimate a typical redshift uncertainty of approximately 0.033(1+z).We determine effective radii from Sersic profile fits to the H-band image using an empirical point-spread function. By supplementing our data with published samples, we propose a mass-dependent size evolution model for passively evolving galaxies, where the most massive galaxies (M(sub ∗) approximately 10(sup 11) solar mass) undergo the strongest evolution from z approximately 2 to the present. Parameterizing the size evolution as (1 + z)(sup - alpha), we find a tentative scaling of alpha approximately equals (−0.6 plus or minus 0.7) + (0.9 plus or minus 0.4) log(M(sub ∗)/10(sup 9 solar mass), where the relatively large uncertainties reflect the poor sampling in stellar mass due to the low numbers of highredshift systems. We discuss the implications of this result for the redshift evolution of the M(sub ∗)-R(sub e) relation for red galaxies.

fundamental parameters↗

NASA NTRS2012

Stellar Populations of Lyman Break Galaxies at z approx. to 1-3 in the HST/WFC3 Early Release Science Observations

We analyze the spectral energy distributions (SEDs) of Lyman break galaxies . (LBGs) at z approx = 1-3 selected using the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) UVIS channel filters. These HST /WFC3 obse,rvations cover about 50 arcmin2 in the GOODS-South field as a part of the WFC3 Early Release Science program. These LBGs at z approx = 1-3 are selected using dropout selection criteria similar to high redshift LBGs. The deep multi-band photometry in this field is used to identify best-fit SED models, from which we infer the following results: (1) the photometric redshift estimate of these dropout selected LBGs is accurate to within few percent; (2) the UV spectral slope f3 is redder than at high redshift (z > 3), where LBGs are less dusty; (3) on average, LBGs at .z approx = 1-3 are massive, dustier and more highly star-forming, compared to LBGs at higher redshifts with similar luminosities, though their median values are similar within 1a uncertainties. This could imply that identical dropout selection technique, at all. redshifts, find physically similar galaxies; and (4) the stellar masses of these LBGs are directly proportional to their UV luminosities with a logarithmic slope of approx 0.46, and star-formation rates are proportional to their stellar masses with a logarithmic slope of approx 0.90. These relations hold true - within luminosities probed in this study - for LBGs from z approx = 1.5 to 5. The star-forming galaxies selected using other color-based techniques show similar correlations at z approx = 2, but to avoid any selection biases, and for direct comparison with LBGs at z > 3, a true Lyman break selection at z approx = 2 is essential. The future HST UV surveys,. both wider and deeper, covering a large luminosity range are important to better understand LBG properties, and their evolution.

Hathi, N. P.↗

NASA NTRS2002

Coronagraphic Imaging with HST and STIS

Revealing faint circumstellar nebulosity and faint stellar or substellar companions to bright stars typically requires use of techniques for rejecting the direct, scattered, and diffracted light of the star. One such technique is Lyot coronagraphy. We summarize the performance of the white-light coronagraphic capability of the Space Telescope Imaging spectrograph, on board the Hubble Space Telescope.

Grady, C. A.↗

NASA NTRS2002

Removing Fringes from STIS Slitless Spectra and WFC3 CCD Images

We have developed a model that allows us to defringe slitless 2-dimensional spectra taken with the Space Telescope Imaging Spectrograph (STIS). An IDL tool has been developed which allows the user to defringe any spectrum obtained with the G750L grating on STIS. This technique has been employed to model the fringing on Wide Field Camera 3 (WFC3) flight candidate CCDs.

Malumuth, E. M.↗

NASA NTRS2000

A Model for Removing Fringes from STIS Slitless Spectra

We have developed a model that allows us to defringe slitless 2-dimensional spectra taken with the Space Telescope Imaging Spectrograph (STIS). Like all thin chip CCDs used in astronomy, the STIS CCD detector acts like an interferometer in the presence of monochromatic light, producing bright and dark fringes where there is constructive and destructive interference. These fringes are especially troublesome for spectra in the near-IR (> 7000A), reaching a peak amplitude of about 20% near 9500 A. Removing fringes from STIS spectra taken with a slit is simply a matter of dividing by an appropriate "fringe flat". A suitable flat is obtained by observing a continuum calibration source through the same slit. This however is not possible for slitless spectra, whose wavelength mapping onto the CCD detector varies with position of the object in the field. Beginning with an approximate knowledge of the STIS CCD structure, we have used 50 continuum source spectral flats taken at various central wavelengths to constrain the thickness of the detection layer at each pixel. Rom this result, we can compute a fringe flat for any astronomical source, no matter how it is positioned in the field. Flats made by this method reduce the fringing amplitude in astronomical spectra by a factor of about 5. The model fringe flat is a function of the index of refraction of each of four layers in the CCD, the thickness of each layer, and the wavelength of the light hitting each pixel. We show how the CCD structural parameters are incorporated into this "fitting function", and describe the procedure used to solve for the free parameters (the thickness of each layer at each pixel). The effectiveness of this technique will be demonstrated using slitless spectra taken as part of the STIS parallel program.

Malumuth, E.M.↗

NASA NTRS1993

Observations of stars with the Hopkins Ultraviolet Telescope

The Hopkins Ultraviolet Telescope (HUT) was flown aboard the space shuttle Columbia as part of the Astron-1 mission during December 1990. During the nine-day flight, HUT carried out 3 A resolution spectrophotometry of a wide variety of astronomical objects, including a number of stellar targets, in the 912-1860 A range of the far ultraviolet. A few nearby stars were observed in the 415-912 A range of the extreme ultraviolet as well. For nearly all of these targets, the spectra obtained by HUT are the first ever obtained in the spectroscopically rich region between Lyman-alpha (1216 A) and the Lyman limit (912 A). Here, we present highlights of the results obtained by HUT in a variety of areas of stellar astronomy.

Kimble, R. A.↗

NASA NTRS1992

Hopkins ultraviolet telescope observations of the far-ultraviolet spectrum of NGC 4151

Observations of the FUV spectrum of the Seyfert galaxy NGC 4151 from 912 to 1860 A during the flight of Astro-1 aboard the space shuttle Columbia in December 1990 are reported. Broad emission lines with full-width at half-maximum of about 8500 km/s dominate the spectrum. Numerous absorption features modify the continuum shape, particularly at wavelengths shortward of Ly-alpha. The continuum turns over sharply below 1000 A and disappears by 924 A, well above the redshifted Lyman edge of NGC 4151 at 915 A. The absorption lines have intrinsic widths of about 1000 km/s and are blueshifted relative to the system velocity of NGC 4151 by 200-1300 km/s. Absorption of the continuum by the converging higher-order Lyman lines explains the sharp turnover of the continuum below 1000 A. The blueshifts of the absorption lines, their large intrinsic widths, and the inferred high densities are all consistent with outflowing material originating in the broad-line region.

Kriss, G. A.↗

NASA NTRS1992

The spectrum of the tropical oxygen nightglow observed at 3 A resolution with the Hopkins Ultraviolet Telescope

Ultraviolet spectra of the tropical oxygen nightglow in the range of 830 to 1850 A (in first order) at 3 A resolution were obtained with the Hopkins Ultraviolet Telescope in December 1990. The data are presented which were obtained on a setting celestial target as the zenith angle of the line-of-sight varied from 77 to 95 deg. The dominant features in the spectrum (other than geocoronal hydrogen) are O I 1304 and 1356 and the radiative recombination continuum near 911 A. The continuum is resolved and found to be consistent with an electron temperature in the range 1000-1250 K. The observed ratio of the brightness of O I 1356 to the continuum suggests that O(+)-O(-) mutual neutralization contributes about 40 percent to the 1356 A emission. The dependence of the optically thin emissions on zenith angle is consistent with a simple ionospheric model. Weak O I 989 emission is also detected, but there is no evidence for any similarly produced atomic nitrogen emissions.

Feldman, P. D.↗

NASA NTRS1991

Determination of ionic abundances in the Io torus using the Hopkins Ultraviolet Telescope

Attention is given to a 415-1864-A spectrum of the emissions from the Io torus with about 3-A resolution in first order (830-1864 A) obtained with HUT in December 1990. A list of the 31 strongest features shows that, apart from five features that are totally or partially terrestrial, all are due to O(+), S(+), S(2+), and S(3+). There is no evidence for elements other than oxygen and sulfur. The spectrum shows many additional weaker emission features so that the existence of minor species cannot be ruled out at this time. Because the HUT spectrum contains well-resolved lines for all four of the major species, the mixing ratio (Ni/ne) for each one can be determined without using models of the spectral emissions, or a detailed geometric model of the torus plasma. The relative concentration of O(+) determined from the HUT observation is 38 percent less than that obtained from the Voyager UVS data.

Moos, H. W.↗

NASA NTRS1991

Observations of Comet Levy (1990c) with the Hopkins Ultraviolet Telescope

Observations of Comet Levy (1990c) were made with the Hopkins Ultraviolet Telescope during the Astro-1 Space Shuttle mission on December 10, 1990. The spectrum, covering the wavelength range 415-1850 A at a spectral resolution of 3 A, shows the presence of carbon monoxide and atomic hydrogen, carbon, and sulfur in the coma. Aside from H I Lyman-beta, no cometary features are detected below 1200 A, although cometary O I and O II would be masked by the same emissions present in the day airglow spectrum. The 9.4 x 116 arcsecond aperture corresponds to 12,000 x 148,000 km at the comet. The derived production rate of CO relative to water is 0.11 + or - 0.02, compared with 0.04 + or - 0.01 derived from IUE observations (made in September 1990) which sample a much smaller region of the coma. This suggests the presence of an extended source of CO, as was found in comet Halley. Upper limits on Ne and Ar abundance are within one order of magnitude of solar abundances.

Feldman, P. D.↗

NASA NTRS1991

Test of the decaying dark matter hypothesis using the Hopkins Ultraviolet Telescope

Sciama's hypothesis that the dark matter associated with galaxies, galaxy clusters, and the intergalactic medium consists of tau neutrinos of rest mass 28-30 eV whose decay generates ultraviolet photons of energy roughly 14-15 eV, has been tested using the Hopkins Ultraviolet Telescope flows aboard the Space Shuttle Columbia. A straightforward application of Sciama's model predicts that a spectral line from neutrino decay photons should be observed from the rich galaxy cluster Abell 665 with an SNR of about 30. No such emission was detected. For neutrinos in the mass range 27.2-32.1 eV, the observations set a lower lifetime limit significantly greater than Sciama's model requires.

Davidsen, A. F.↗