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Carbon and Nitrogen Abundances Determined from Transition Layer Lines
Mena-Werth, Jose; Boehm-Vitense, Erika
The possibility of determining relative carbon, nitrogen, and silicon abundances from the emission-line fluxes in the lower transition layers between stellar chromospheres and coronae is explored. Observations for main-sequence and luminosity class IV stars with presumably solar element abundances show that for the lower transition layers Em = BT<…
Rotation and Transition Layer Emission in Cool Giants
Boehm-Vitense, Erika
Gray (1981, 1982) found that field giants with T(eff) less than about 5500 K experience a steep decrease in rotational velocities coupled with a decrease in transition layer emission. This decrease may be attributable to fast magnetic braking or to redistribution of angular momentum for rapidly increasing depths of the convection zones if these ro…
A study of the optical and ultraviolet spectral characteristics and the circumstellar material around the new luminous blue variable WRA 751.
Perez, M. R.; The, P. S.; de Winter, D. +1 more
The LBV characteristics of the new LBV candidate WRA 751 suggested by Hu et al. (1990) are studied in greater detail. A comparison is made with observational characteristics of the well-known LBVs Ag Car and HR Car using photometric and spectroscopic data of Hu et al. supplemented with an IUE spectrum and direct CCD images in H-alpha, blue, and re…
The Characteristics and Origin of the Gould's Belt
Torra, J.; Comeron, F.; Gomez, A. E.
Some statistical studies on the nearby early-type stars proposed for observations by HIPPARCOS are presented. Results on spatial orientation and kinematics are in agreement with those found in the literature. An age estimate based on non-kinematical hypothesis is found to be somewhat smaller than expansion ages derives by some authors. Finally, it…
A new kind of oscillation in the persistent emission of the Rapid Burster.
Stella, Luigi; Lewin, Walter H. G.; van Paradijs, Jan +3 more
We present a study of a new kind of oscillation found in the persistent emission after some type II bursts from the Rapid Burster observed during 1985 August with EXOSAT. All 95 bursts observed were longer than 30 s. Ten of them were followed by these oscillations. The frequency of the oscillations ranged from 39 to 56 mHz. A period decrease (by 3…
The active phase of the symbiotic star BF Cygni.
Gonzalez-Riestra, R.; Cassatella, A.; Fernandez-Castro, T. +1 more
The activity phase of BF Cygni discovered in May 1989 and which lasted about two years is examined. The UV emission lines, usually strong during quiescence, were not detectable during the outburst. UV high-resolution spectra in the outburst indicate the development of an expanding shell giving rise to a considerable number of violet-shifted absorp…
The Binary Cepheid BP Cir: A Test of Evolutionary Tracks
Arellano Ferro, A.; Evans, Nancy R.; Udalska, Joanna
IUE spectra of the system containing the Cepheid BP Cir are used to derive the magnitude difference between the two stars (Δ V = 1.88 ± 0.3 mag) and the spectral type of the companion (B6.OV). This is the first system yet encountered for which the standard Seaton reddening law is inappropriate. For BP Cir, a stronger 2200 Å bump than the standard …
Mg II absolute line profiles for late-type stars and for spatially-resolved solar regions.
Pallavicini, R.; Cerruti-Sola, M.; Cheng, C. -C.
The authors present the results of a comparison of Mg II h and k line profiles and fluxes for late-type stars observed with IUE and for spatially resolved solar regions observed at comparable resolution by the NRL Spectrograph on Skylab. They show that the spatially resolved solar observations are in good agreement with the disk integrated stellar…
High-precision VLBI astrometry of the radio-emitting star sigma rho a step in linking the HIPPARCOS and extragalactic reference frames.
Preston, Robert A.; Lestrade, Jean-Francois; Phillips, Robert B. +1 more
VLBI observations of the optically bright radio-emitting star Sigma Coronae Borealis (Sigma CrB) have yielded its position relative to an angularly nearby quasar, its annual proper motion and its trigonometric parallax with formal uncertainties slightly better than 0.2 milliarcsec. This is the first result of the VLBI astrometric program we are co…
Photometric calibration of the International Ultraviolet Explorer (IUE) at low resolution: the LWP camera.
Gonzalez-Riestra, R.; Lloyd, C.; Cassatella, A. +2 more
The authors present and discuss the low resolution absolute calibration for the LWP camera of the International Ultraviolet Explorer (IUE). The calibration, implemented in routine processing of LWP low resolution images on December 22, 1987 at both GSFC and VILSPA IUE ground stations, is based on the last set of Intensity Transfer Function (ITF2) …