Search Publications
A Search for Signatures of Quasar Evolution: Comparison of the Shapes of the Rest-Frame Optical/Ultraviolet Continua of Quasars at z>3 and z~0.1
Elvis, Martin; Bechtold, Jill; Elston, Richard +1 more
For 15 bright (V<17.5), high-redshift (z>3) quasars, we have obtained infrared spectra and photometry, and optical spectrophotometry and photometry, which we use to construct their spectral energy distributions (SEDs) from λrest~1285-5100 Å. High-resolution spectroscopy for seven enable measurements of their continua shortward of …
IUE Absorption-Line Observations of the Moderately and Highly Ionized Interstellar Medium toward 164 Early-Type Stars
Sembach, Kenneth R.; Savage, Blair D.; Meade, Marilyn R.
We present measurements of Galactic interstellar Al III, Si IV, and C IV absorption recorded in high-resolution archival ultraviolet spectra of 164 hot early-type stars observed by the International Ultraviolet Explorer (IUE) satellite. The objects studied were drawn from the list of hot stars scheduled to be observed with the Far Ultraviolet Spec…
Physical Conditions in the Foreground Gas of Reflection Nebulae: NGC 2023, vdB 102, and NGC 7023
Federman, S. R.; Lambert, David L.; Yan, M. +2 more
High-resolution optical spectra of HD 37903 and HD 147009, which illuminate the reflection nebulae NGC 2023 and vdB 102, were obtained for comparison with our results for HD 200775 and NGC 7023. Ground-based measurements of the molecules CH, C2, and CN and the atoms Na I and K I were analyzed to extract physical conditions in the foregr…
New Rest Wavelength Determinations for Seven Mid-Infrared Fine-Structure Lines by ISO-SWS
Lutz, D.; Beintema, D. A.; Feuchtgruber, H.
Observations of the planetary nebulae NGC 6302, NGC 6543, and NGC 7027 by the Short Wavelength Spectrometer (SWS) on board the Infrared Space Observatory (ISO) have been used to determine rest wavelengths of spectral lines. We report on improved accuracies for wavelengths of seven mid-infrared ionic fine-structure lines. Based on observations made…
Emission-Line Ratios for [N II] in Gaseous Nebulae and a Comparison between Theory and Observation
Feibelman, W. A.; Keenan, F. P.; Aller, L. H. +1 more
R-matrix calculations of electron impact excitation rates among the 2s22p2 3P, 1D, 1S, and 2s2p3 5S levels of N II are presented. These results are used in conjunction with other recent calculations of electron impact excitation rates and Einstein A-coefficients for N II …
Planetary Nebula He 2-36: Still Enigmatic, But Getting Less So
Feibelman, Walter A.; Kondo, Yoji
IUE spectra of He 2-36 indicate that the stellar C IV λ1549 doublet varies in intensity by a factor of 2.5 during a one-year interval. Detection of [Ne IV] λ2424, plus previously known He II and C IV, argue for a hot companion to the cool A2 III nucleus. The C IV emission shows a split profile that strongly resembles the profile (reprocessed in th…
Discovery of DampedLyα Systems at Redshifts Less than 1.65 and Results on Their Incidence and Cosmological Mass Density
Turnshek, David A.; Rao, Sandhya M.
We present results from an efficient, nontraditional survey to discover damped Lyα (DLA) absorption systems with neutral hydrogen column densities NHI>=2×1020 atoms cm-2 and redshifts z<1.65. In the past, identification of DLA systems at z<1.65 has been difficult because of their rare incidence and the nee…
A Database of Cepheid Distance Moduli and Tip of the Red Giant Branch, Globular Cluster Luminosity Function, Planetary Nebula Luminosity Function, and Surface Brightness Fluctuation Data Useful for Distance Determinations
Kelson, Daniel D.; Illingworth, Garth D.; Madore, Barry F. +14 more
We present a compilation of Cepheid distance moduli and data for four secondary distance indicators that employ stars in the old stellar populations: the planetary nebula luminosity function (PNLF), the globular cluster luminosity function (GCLF), the tip of the red giant branch (TRGB), and the surface brightness fluctuation (SBF) method. The data…
Models for Old, Metal-Poor Stars with Enhanced α-Element Abundances. II. Their Implications for the Ages of the Galaxy's Globular Clusters and Field Halo Stars
VandenBerg, Don A.
The ages of globular clusters (GCs) and post-turnoff field stars in the Galactic halo are derived using new stellar evolutionary models that explicitly take into account the observed abundances of the α-elements. Whereas the distances of the field subgiants considered in this study are based on Hipparcos parallax measurements, theoretical zero-age…
Low- and High-Ionization Absorption Properties of Mg II Absorption-selected Galaxies at Intermediate Redshifts. I. General Properties
Charlton, Jane C.; Schneider, Donald P.; Steidel, Charles C. +4 more
We present extensive metal-line absorption properties for 45 absorption systems that were selected by their Mg II absorption at redshifts between 0.4 and 1.4. For each system the properties of several chemical species are determined, including a wide range of ionization conditions. In the optical, the absorption systems have been observed at ~6 km…