Search Publications
Calibrating Array Detectors
Fixsen, D. J.; Arendt, R. G.; Moseley, S. H.
The development of sensitive large-format imaging arrays for the infrared promises to provide revolutionary capabilities for space astronomy. For example, the Infrared Array Camera (IRAC) on SIRTF will use four 256×256 arrays to provide background limited high spatial resolution images of the sky in the 3 to 8 µm spectral region. In order to…
Nuclear Gas and Dust Disks in Nearby 3CR Elliptical Galaxies
Baum, Stefi A.; Sparks, William B.; Turner, Neal J. +1 more
Using WFPC2 V, R, I, and Hα+[N II] images, we examine the morphologies, environments, colors, and line emission of dust and gas disks located in the cores of seven low-redshift elliptical galaxies hosting 3C radio sources: NGC 383 (3C 31)/NGC 382, NGC 547 (3C 40), NGC 3862 (3C 264), NGC 4261 (3C 270), NGC 5532 (3C 296), NGC 7720 (3C 465)/NGC 7720A…
Theoretical Oscillator Strengths inPr III and Application to Some CP Stars
Quinet, P.; Frémat, Y.; Palmeri, P. +2 more
A set of transition probabilities is obtained for the first time for many transitions of Pr III of astrophysical interest. A relativistic Hartree-Fock method, combined with a least-squares fitting of the available experimental levels, including a large number of newly determined values, has been used for the calculations in which configuration int…
Charged-Particle Resonance Conditions and Transport Coefficients in Slab-Mode Waves
Vainio, R.
Transport of charged particles in cold plasma is considered. The full dispersion relation for slab-mode waves is employed, and the quasi-linear particle scattering is discussed. Previous results of the dispersive-wave model on the ion mean free path are recalled and further developed. For small cross-helicities, the model predicts ion mean free pa…
The Structure of Wolf-Rayet Winds. II. Observations of Ionization Stratification in the WN Subtype
Morris, P.; Herald, J. E.; Schulte-Ladbeck, R. E. +1 more
Motivated by the question of the importance of ionization stratification in solving the ``momentum problem'' of Wolf-Rayet stellar winds, we have chosen a sample of 14 WN stars for a systematic study. We performed measurements of the emission line widths on ultraviolet, optical, and infrared spectra to obtain data spanning a large range of ionizat…
Structural Characteristics of Faint Galaxies Serendipitously Discovered with the Hubble Space Telescope WFPC2
Impey, C. D.; Bothun, G. D.; O'Neil, Karen
Utilizing the F814W and F300W filters, Hubble Space Telescope Wide Field Planetary Camera-2 (WFPC2) images were taken of four low surface brightness galaxies in the direction of the Virgo Cluster--V7L3, V2L8, V1L4, and Malin 1. The high resolution of the WFPC2 combined with the extremely diffuse nature of the four galaxies makes them essentially t…
The Ulysses Supplement to the Granat/WATCH Catalog of Cosmic Gamma-Ray Bursts
Cline, T.; Hurley, K.; Sunyaev, R. +7 more
We present third Interplanetary Network (IPN) localization data for 56 gamma-ray bursts in the Granat/WATCH catalog that occurred between 1990 November and 1994 September. These localizations are obtained by triangulation using various combinations of spacecraft and instruments in the IPN, which consisted of Ulysses, BATSE, Pioneer Venus Orbiter, …
The Local Interstellar Medium in Puppis-Vela
Blaauw, A.; Moos, H. Warren; Sahu, M. S. +1 more
The first study of the local interstellar medium (LISM) toward Puppis-Vela (l=245deg to 275°, b=-15deg to +5°, d<200 pc) is presented in this paper. A study of the locations, sizes, and physical characteristics of local interstellar gas, i.e.``astronephography,'' is included, and relies upon the improved distance measureme…
Hubble Space Telescope Observations of the Shocks in Supernova Remnant SN 1987A
Michael, Eli
We present observations of supernova remnant SN 1987A made with the Hubble Space Telescope. The bright spot previously observed on the inner circumstellar ring by the Wide Field/Planetary Camera at a position angle ~31deg has brightened by nearly a factor of 2 in seven months. Space Telescope Imaging Spectrograph (STIS) spectra confirm …
Using Balmer Line Shapes to Diagnose Physical Conditions in Collisionless Shock Waves
Hartigan, Patrick; Raymond, John C.; Ghavamian, Parviz
When a collisionless shock propagates through a partially ionized, tenuous medium (n<=1 cm-3), the neutral atoms overrun by the shock produce Balmer line emission as they are excited by collisions in the hot postshock gas. The collisional excitation of neutral atoms and their charge exchange with hot postshock protons produces both n…