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The Distribution of Thermal Pressures in the Interstellar Medium from a Survey of C I Fine-Structure Excitation
Tripp, Todd M.; Jenkins, Edward B.
We used the Space Telescope Imaging Spectrograph (STIS) with its smallest entrance aperture (0.03" wide slit) and highest resolution echelle gratings (E140H and E230H) to record the interstellar absorption features for 10 different multiplets of neutral carbon at a resolving power of λ/Δλ=200,000 in the UV spectra of 21 early-type stars. Our objec…
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…
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…