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ROSAT and HIPPARCOS Observations of Isolated Pre-Main-Sequence Stars near HD 98800
Cohen, David H.; Jensen, Eric L. N.; Neuhäuser, Ralph
We present new observations of the isolated young stars HD 98800 and CD -33 deg7795. Pointed ROSAT observations show that their X-ray properties, including X-ray luminosity and variability, are consistent with those of pre-main-sequence (PMS) stars. These observations do not reveal any additional PMS candidates in 40' fields centered on HD 98800 a…
Broad Emission Line Variability as a Constraint upon the Physical Conditions within the Broad Emission Line Region of NGC 5548
Goad, Mike; Koratkar, Anuradha
Using a Gaussian fitting procedure, we have constructed an accurate UV narrow emission line template spectrum for the Seyfert 1 galaxy NGC 5548, from the low-state Hubble Space Telescope/Faint Object Spectrograph UV spectrum taken on 1982 July 5 with the 1.0" circular aperture. This template spectrum is similar in form to that determined for the p…
Hubble Space Telescope ultraviolet spectroscopy of the supersoft X-ray binaries CAL83 and RXJ0513.9-6951
Gänsicke, B. T.; Beuermann, K.; de Martino, D. +1 more
We present Hubble Space Telescope ultraviolet observations with the Goddard High Resolution Spectrograph of the supersoft X-ray binaries CAL83 and RXJ0513.9-6951 in the Large Magellanic Cloud. Both sources show a remarkably similar spectrum with an almost flat continuum and weak \N V and \O V emission lines. The neutral hydrogen column densities d…
The Si/Ne Abundance Ratio in Polar Coronal Hole and Quiet-Sun Coronal Regions
Wilhelm, K.; Schühle, U.; Lemaire, P. +4 more
Using spectra obtained from the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer flown on the Solar and Heliospheric Observatory (SOHO) spacecraft, we determine the Si/Ne abundance ratio in diffuse, interplume polar coronal hole regions, as well as the ratio relative to quiet-Sun coronal regions. Ne has the second highest f…
Surface gravities of very metal-poor stars from HIPPARCOS parallaxes
Fuhrmann, Klaus
We discuss some consequences for the determination of the surface gravity parameter of very metal-poor halo dwarfs in the new light shed upon these objects from the Hipparcos astrometry. Whereas it has become clear that standard spectroscopic LTE iron ionization equilibria are prone to systematic errors, in the sense, that stages of evolution are …
Effective temperature of detached eclipsing binaries from HIPPARCOS parallax
Ribas, I.; Jordi, C.; Torra, J. +2 more
Effective temperatures of detached eclipsing binaries computed through Hipparcos trigonometric parallaxes are compared with the photometric determinations. The former are based on the values of the radius, the apparent visual magnitude and the bolometric correction of the star, whereas the latter are obtained from standard calibrations using Strom…
The Age Range of Hyades Stars
Eggen, Olin J.
On the basis of canonical models, the age of Hyades supercluster stars, whether in the Hyades and Praesepe clusters or the noncluster field, ranges from (5-6) x 10^8 to 10^9 yr. The difference between the parallax derived from the supercluster motion and that obtained from Hipparcos observations has a dispersion only twice that of the mean dispers…
The Hubble Space Telescope Key Project on the Extragalactic Distance Scale. XII. The Discovery of Cepheids and a New Distance to NGC 2541
Illingworth, Garth D.; Madore, Barry F.; Freedman, Wendy L. +17 more
We report the detection of Cepheids and a new distance to the spiral galaxy NGC 2541, based on data obtained with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope (HST). A total of 25 exposures (divided into 13 epochs) were obtained using the F555W filter (transformed to Johnson V), and nine exposures were obtained (divided in…
Time-dependent structure in ultraviolet absorption lines of the rapid rotators HD 64760 (B0Ib) and HD 93521 (O9.5V)
Massa, D.; Prinja, R. K.; Howarth, Ian D. +5 more
Cross-correlation provides an effective line-averaging function for spectra containing many line features, a result which can be exploited in order to perform time-series and spatial-domain analyses of absorption-line variability in data of (relatively) poor quality. We apply this method to high-resolution IUE spectra. For the known non-radial pul…
A Spherical Non-LTE Line-blanketed Stellar Atmosphere Model of the Early B Giant epsilon Canis Majoris
Hauschildt, P. H.; Baron, E.; Shore, S. N. +1 more
We use a spherical non-LTE fully line-blanketed model atmosphere to fit the full multiwavelength spectrum, including the extreme-ultraviolet (EUV) continuum observed by the Extreme Ultraviolet Explorer, of the B2 II star ɛ Canis Majoris (CMa). The available spectrophotometry of ɛ CMa from 350 Å to 25 µm is best fitted with model parameters T…