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Full-Text Articles in Stars, Interstellar Medium and the Galaxy
Spectral Energy Distribution Signatures Of Jovian Planets Around White Dwarf Stars., R. Ignace
Spectral Energy Distribution Signatures Of Jovian Planets Around White Dwarf Stars., R. Ignace
Richard Ignace
The problem of detecting Jovian-sized planets orbiting white dwarf stars is considered. Significant IR excesses result from warm Jupiters orbiting a white dwarf of Teff = 10,000 K at a distance of ~103 white dwarf radii (corresponding to ~102 Jupiter radii or a few tenths of an AU) with an orbital period of ~100 days. Such a planet will have a 10 µm flux density at its Wien peak that is comparable to the emission of the white dwarf at that wavelength. Although the white dwarf is much hotter than the planet, the planet will have peak …
Line Forces In Keplerian Circumstellar Disks And Precession Of Nearly Circular Orbits., K. G. Gayley, R. Ignace, S. P. Owocki
Line Forces In Keplerian Circumstellar Disks And Precession Of Nearly Circular Orbits., K. G. Gayley, R. Ignace, S. P. Owocki
Richard Ignace
We examine the effects of optically thick line forces on orbiting circumstellar disks, such as occur around Be stars. For radially streaming radiation, line forces are only effective if there is a strong radial velocity gradient, as occurs, for example, in a line-driven stellar wind. However, within an orbiting disk, the radial shear of the azimuthal velocity leads to strong line-of-sight velocity velocity gradients along nonradial directions. As such, in the proximity of a stellar surface extending over a substantial cone angle, the nonradial stellar radiation can impart a significant line force, even in the case of purely circular orbits. …
Terminal Speeds And Ion Fractions From [Caiv] 3.207 Μm In Three Single Wn Stars., Richard Ignace
Terminal Speeds And Ion Fractions From [Caiv] 3.207 Μm In Three Single Wn Stars., Richard Ignace
Richard Ignace
We report on the forbidden emission lines of [CaIV] at 3.207 μm and [NeIII] at 15.56 μm based on Infrared Space Observatory observations. The data set consists of three single Wolf-Rayet stars (WR 1, WR 134, and WR 136) and three binary systems (WR 11, WR 146, and WR 147). For the single stars, only the [CaIV] line was observed. Our primary objectives are to determine the wind terminal speed from the emission-line widths, derive ion number fractions, and discuss the relation between emission profile shapes and wind flow geometry. Compared to previous determinations of the terminal speed, we find …
Modelling X-Ray Variability In The Structured Atmospheres Of Hot Stars., L. M. Oskinova, R. Ignace, J. C. Brown, J. P. Cassinelli
Modelling X-Ray Variability In The Structured Atmospheres Of Hot Stars., L. M. Oskinova, R. Ignace, J. C. Brown, J. P. Cassinelli
Richard Ignace
We describe X-ray production in the atmospheres of hot, early-type stars in the framework of a "stochastic shock model". The extended envelope of a star is assumed to possess numerous X-ray emitting "hot" zones that are produced by shocks and embedded in the ambient "cold" medium in dynamical equilibrium. It is shown that the apparent lack of X-ray variability on short (similar to hours) timescales do not contradict a shock model for X-ray production. The character of the X-ray variability is found to depend on the frequency with which hot zones are generated, the cool wind opacity to X-rays, and …
Theoretical Profile Shapes For Optically Thin X-Ray Emission Lines From Spherical Stellar Winds., R. Ignace
Theoretical Profile Shapes For Optically Thin X-Ray Emission Lines From Spherical Stellar Winds., R. Ignace
Richard Ignace
One of the major outstanding problems in hot star wind theory is an understanding of the observed X-ray emissions from the early-type B, O, and Wolf-Rayet (WR) stars. The latest X-ray satellites Chandra and XMM-Newton are providing key new observations of resolved emission profiles to advance that understanding. This study presents a derivation of the expected emission-line profiles, assuming optically thin line emission and spherical symmetry, with a proper treatment of the attenuation of X-rays by the dense cool wind component. Examples of line profile variability for a narrow outflowing shell are presented. Then the case of embedded hot gas …
The Hanle Effect As A Diagnostic Of Magnetic Fields In Stellar Envelopes Iii. Including The Finite Star Depolarization Effect., R. Ignace
Richard Ignace
The Hanle effect is a relatively new magnetic diagnostic in stellar astrophysics. Although a substantial literature exists for applications of the Hanle effect in solar studies, the Hanle effect is only a fledgling subject in stellar astrophysics, with previous work focusing on simplistic cases to isolate the magnetic effects on polarized resonance scattering line profiles. In particular, applications to stars have treated the star as a point source of illumination. This paper carries the work forward by considering the consequences of finite stellar size for the line polarization. An approach based on intensity moments is derived. For optically thin line …