Search Publications
Notes on the convection in the ATLAS9 model atmospheres.
Castelli, F.; Gratton, R. G.; Kurucz, R. L.
The mixing-length theory for the convection, as it is used in the ATLAS9 code (Kurucz, 1993a), is summarized and discussed. We investigated the effect of the modification called ``approximate overshooting'' on the model structure of the Sun and of stars with T_eff_ included between 4000K and 8500K, logg included between 2.5 and 4.5, and metallicit…
Line-blanketed model atmospheres for R Coronae Borealis stars and hydrogen-deficient carbon stars.
Eriksson, K.; Gustafsson, B.; Asplund, M. +1 more
We have constructed line-blanketed model atmospheres for the hydrogen-deficient and carbon-rich R Coronae Borealis (RCrB) stars, as well as for the similar hydrogen-deficient carbon (HdC) stars and the cool extreme helium (EHe) stars. Improved continuum opacities have been used together with realistic line absorption data for atomic and molecular …
Optical-IUE observations of the gamma-ray loud BL Lacertae object S5 0716+714: data and interpretation.
Maraschi, L.; Ghisellini, G.; Pian, E. +14 more
We monitored the BL Lac object S5 0716+714 in the optical band during the period November 1994 - April 1995, which includes the time of a γ-ray observation by the Energetic Gamma Ray Experiment Telescope (EGRET) on February 14-28, 1995. The light curves in the R and B bands show fast fluctuations superimposed on longer timescale variations. The co…
Patchy intergalactic He II absorption in HE 2347-4342. II. The possible discovery of the epoch of He-reionization
Reimers, D.; Wamsteker, W.; Rodriguez-Pascual, P. +3 more
We report on observations of redshifted Heii303.8 Angstroms absorption in the high-redshift QSO HE2347-4342 (z=2.885, V=16.1) with the Goddard High Resolution Spectrograph on board HST in its low resolution mode (bigtriangleup lambda = 0.7 Angstroms). With f_λ=3.6\ 10(-15) ergcm(-2) s(-1) Angstroms(-1) at the expected position of Heii304 Angstroms…
Cataclysmic variables in the ROSAT PSPC All Sky Survey.
Verbunt, F.; Bunk, W. H.; Ritter, H. +1 more
91 cataclysmic variables from a sample of 162 systems with known or suspected binary periods were detected during the ROSAT XRT-PSPC All Sky Survey. Among the non-magnetic systems, the X-ray to optical/ultraviolet flux ratio decreases along the sequence SU UMa type - U Gem type - Z Cam type - UX UMa type, due mainly to variations in the optical/ul…
Fundamental parameters of Wolf-Rayet stars. VI. Large Magellanic Cloud WNL stars.
Crowther, P. A.; Smith, L. J.
We present a detailed, quantitative study of late WN (WNL) stars in the LMC, based on new optical spectroscopy (AAT, MSO) and the Hillier (1990A&A...231..111H) atmospheric model. In a previous paper (Crowther et al. 1995A&A...293..172C), we showed that 4 out of the 10 known LMC Ofpe/WN9 stars should be re-classified WN9-10. We now present …
Coordinated ultraviolet and Hα spectroscopy of bright O-type stars.
Kaper, L.; Kambe, E.; Fullerton, A. W. +7 more
As part of our search for the origin of stellar-wind variability, we have conducted simultaneous ultraviolet and Hα spectroscopy of a number of bright O stars. The observed changes in the Hα line occur at low velocity (0-0.2vinfinity_) on timescales that are characteristic of the development and evolution of discrete absorption componen…
Wind variability of B supergiants. III. Corotating spiral structures in the stellar wind of HD 64760.
Owocki, S. P.; Cranmer, S. R.; Prinja, R. K. +2 more
Fourier analysis of two spectroscopic time series obtained with the IUE observatory confirm that the ultraviolet stellar wind profiles of HD 64760 (B0.5 Ib) are periodically variable. The periodic component consists of modulations that extend over most of the P Cygni absorption trough, and can frequently be traced through the emission lobe. The mo…
Spectral analyses of central stars of planetary nebulae of early WC-type NGC 6751 and Sanduleak 3.
Hamann, W. -R.; Koesterke, L.
The two Wolf-Rayet type central stars of the planetary nebulae NGC 6751 and Sanduleak 3, showing the early spectral subtypes [WC4] and [WC2-3], respectively, are analyzed by means of non-LTE models for spherically expanding atmospheres. Complex model atoms of helium, carbon, oxygen and nitrogen are taken into account. For the atmospheric compositi…
The distinction between OIafpe and WNLha stars. A spectral analysis of HD 151804, HD 152408 and HDE 313846.
Crowther, P. A.; Bohannan, B.
From detailed atmospheric analysis of the Galactic late O supergiants, HD 151804 (O8Iaf) and HD 152408 (O8:Iafpe) and the morphologically related Wolf-Rayet star, HDE 313846 (WR108; WN9ha) we conclude that little distinguishes the overall structure and composition of the stellar atmosphere of HD 152408 from HDE 313846, such that HD 152408 could be…