Search Publications
Stellar Iron Abundances: Non-LTE Effects
Thévenin, F.; Idiart, T. P.
We report new statistical equilibrium calculations for Fe I and Fe II in the atmosphere of late-type stars. We used atomic models for Fe I and Fe II having, respectively, 256 and 190 levels, as well as 2117 and 3443 radiative transitions. Photoionization cross sections are from the Iron Project. These atomic models were used to investigate non-LTE…
An Empirical Model of a Polar Coronal Hole at Solar Minimum
Romoli, M.; Raymond, J. C.; Naletto, G. +28 more
We present a comprehensive and self-consistent empirical model for several plasma parameters in the extended solar corona above a polar coronal hole. The model is derived from observations with the SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) during the period between 1996 November and 1997 April. We compare observations of H I Lyα and O …
15 Micron Infrared Space Observatory Observations of the 1415+52 Canada-France Redshift Survey Field: The Cosmic Star Formation Rate as Derived from Deep Ultraviolet, Optical, Mid-Infrared, and Radio Photometry
Omont, A.; Eales, S.; Thuan, T. X. +7 more
The Canada-France Redshift Survey 1452+52 field has been deeply imaged with the Infrared Space Observatory using ISOCAM through the LW3 filter (12-18 µm). Careful data analysis and comparison with deep optical and radio data have allowed us to generate a catalog of 78 15 µm sources with both radio and optical identifications. They are …
Observations of Solid Carbon Dioxide in Molecular Clouds with the Infrared Space Observatory
de Graauw, Th.; Prusti, T.; van Dishoeck, E. F. +8 more
Spectra of interstellar CO2 ice absorption features at a resolving power of λ/Δλ~1500-2000 are presented for 14 lines of sight. The observations were made with the Short-Wavelength Spectrometer (SWS) of the Infrared Space Observatory (ISO). Spectral coverage includes the primary stretching mode of CO2 near 4.27 µm in al…
On the Doppler Shifts of Solar Ultraviolet Emission Lines
Peter, H.; Judge, P. G.
We examine emission-line profiles observed with the Solar Ultraviolet Measurement of Emitted Radiation (SUMER) instrument during the roll of the SOHO spacecraft on 1997 March 20. SUMER data were acquired in selected wavelength bands including lines from the low chromosphere to the corona. Our main aim is to determine the center-to-limb behavior of…
Metal Abundances at z<1.5: Fresh Clues to the Chemical Enrichment History of Damped Lyα Systems
Bowen, David V.; Pettini, Max; Ellison, Sara L. +1 more
We explore the redshift evolution of the metal content of damped Lyα systems (DLAs) with new observations of four absorbers at z<1.5 together with other recently published data, there is now a sample of 10 systems at intermediate redshifts for which the abundance of Zn has been measured. The main conclusion is that the column density-weighted m…
Spectroscopic Constraints on Models of Ion Cyclotron Resonance Heating in the Polar Solar Corona and High-Speed Solar Wind
Kohl, John L.; Cranmer, Steven R.; Field, George B.
Using empirical ion velocity distributions derived from Ultraviolet Coronagraph Spectrometer (UVCS) and Solar Ultraviolet Measurements of Emitted Radiation (SUMER) ultraviolet spectroscopy, we construct theoretical models of the nonequilibrium plasma state of the polar solar corona. The primary energy deposition mechanism we investigate is the dis…
Three-dimensional Stereoscopic Analysis of Solar Active Region Loops. I. SOHO/EIT Observations at Temperatures of (1.0-1.5) × 106 K
Klimchuk, J. A.; Aschwanden, Markus J.; Gary, G. Allen +5 more
The three-dimensional structure of solar active region NOAA 7986 observed on 1996 August 30 with the Extreme-Ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO) is analyzed. We develop a new method of dynamic stereoscopy to reconstruct the three-dimensional geometry of dynamically changing loops, which allows…
Dust and Extinction Curves in Galaxies with z>0: The Interstellar Medium of Gravitational Lens Galaxies
Peng, C. Y.; Keeton, C. R.; Kochanek, C. S. +6 more
We determine 37 differential extinctions in 23 gravitational lens galaxies over the range 0<~zl<~1. Only seven of the 23 systems have spectral differences consistent with no differential extinction. The median differential extinction for the optically selected (radio-selected) subsample is ΔE(B-V)=0.04 (0.06) mag. The extinction i…
NICMOS Imaging of the HR 4796A Circumstellar Disk
Schneider, Glenn; Hines, Dean C.; Terrile, Richard J. +7 more
We report the first near-infrared (NIR) imaging of a circumstellar annular disk around the young (~8 Myr), Vega-like star HR 4796A. NICMOS coronagraph observations at 1.1 and 1.6 µm reveal a ringlike symmetrical structure that peaks in reflected intensity 1.05"+/-0.02" (~70 AU) from the central A0 V star. The ring geometry, with an inclinati…