Search Publications

Hubble Deep Field Constraint on Baryonic Dark Matter

Gould, Andrew; Bahcall, John N.; Flynn, Chris

We use a new technique to search for faint red stars in the Hubble deep field. We distinguish unambiguously between stars and galaxies to I = 26.3. Our results place strong and general constraints on the I-band luminosity of the constituents of the Galactic dark halo.

Spectrophotometric Standards From the Far-UV to the Near-IR on the White Dwarf Flux Scale

Bohlin, Ralph C.

The second generation instruments to be installed in 1997 on the Hubble Space Telescope (HST) require spectrophotometric standard stars for flux calibrations to 1.1 µm for the imaging spectrograph (STIS) and to 2.5 µm for the infrared camera (NICMOS). Calculated model atmosphere flux distributions from 0.1 to 3 µm for four pure h…

Hubble Space Telescope Observations of the HH 47 Jet: Narrowband Images

Hartigan, Patrick; Bally, John; Schwartz, Richard D. +4 more

Detection of Ozone on Ganymede

Johnson, Robert E.; Weaver, Harold A.; Noll, Keith S. +2 more

An absorption band at 260 nanometers on the trailing hemisphere of Ganymede, identified as the Hartley band of ozone (O_3), was measured with the Hubble Space Telescope. The column abundance of ozone, 4.5 x 10¹⁶ per square centimeter, can be produced by ion impacts or by photochemical equilibrium with previously detected molecular oxyge…

Infrared spectrophotometry of M 17 with ISOCAM.

Palazzi, E.; Perault, M.; Abergel, A. +4 more

We report spectrophotometric observations of the HII region/neutral medium interface in M 17 obtained with the ISOCAM Circular Variable Filter (CVF) in the spectral range 5.15 to 16.5µm. The lines of singly-ionized species come mainly from the clumpy "neutral" interface, while the HII region dominates the line emission by higher-ionization s…

SWS observations of solid CO_2_ in molecular clouds.

Lutz, D.; Heras, A. M.; Prusti, T. +29 more

We report absorption features of solid CO_2_ stretching and bending modes in several lines of sight, including embedded young stellar objects and the Galactic Center source Sgr A*. The overall CO_2_ abundance in ices is ~15% relative to H_2_O. Profile shapes are consistent with the presence of grain mantles with distinct polar (H_2_O-rich) and non…

The Dark Matter, Gas, and Galaxy Distributions in Abell 2218: A Weak Gravitational Lensing and X-Ray Analysis

Babul, A.; Kaiser, N.; Neumann, D. M. +4 more

We report on the detection of dark matter in the cluster Abell 2218 using the weak gravitational distortion of background galaxies. We find a highly significant, coherent detection of the distortion in the images of the background galaxies. We use Hubble Space Telescope (HST) images from the Medium Deep Survey to calibrate the suppression in the o…

2.5-45µm SWS spectroscopy of the Circinus Galaxy.

Lutz, D.; Genzel, R.; Sturm, E. +5 more

We present 2.5-45µm ISO SWS spectra of the Circinus galaxy which is one of the closest spirals containing both a visually obscured Seyfert nucleus and circumnuclear starburst activity. In addition to PAH features, H_2_ and low excitation ionic lines ([FeII], [NeII], [SIII]) from the starburst region its spectrum shows several prominent lines…

WFPC2 Studies of the Crab Nebula. III. Magnetic Rayleigh-Taylor Instabilities and the Origin of the Filaments

Casertano, Stefano; Ballester, Gilda E.; Crisp, David +18 more

Recently obtained Hubble Space Telescope WFPC2 images of the Crab Nebula show that the emission-line filaments are dominated by structures that morphologically appear to be the result of magnetic Rayleigh- Taylor (R-T) instabilities at the interface between the pulsar-driven synchrotron nebula and a shell of swept- up ejecta. We replace this morph…

Cepheid Calibration of the Peak Brightness of Type IA Supernovae: Calibration of SN 1990N in NGC 4639 Averaged with Six Earlier Type IA Supernova Calibrations to Give H 0 Directly

Panagia, N.; Saha, A.; Labhardt, Lukas +3 more

Periods and light curves have been measured with the Hubble Space Telescope for 20 Cepheids in NGC 4639, parent galaxy to the Type Ia, prototypical supernova SN 1990N. The periods range from 17 to 69 days. The mean apparent magnitudes, averaged over the light curves, range from <V> = 25.6 to <V> = 27.3. Well-determined period-luminosit…