Physical Sciences and Mathematics Commons^™

An X-Ray Study Of Two B+B Binaries: Ah Cep And Cw Cep, Richard Ignace, K. T. Hole, Lidia M. Oskinova, J. P. Rotter

ETSU Faculty Works

AH Cep and CW Cep are both early B-type binaries with short orbital periods of 1.8 days and 2.7 days, respectively. All four components are B0.5V types. The binaries are also double-lined spectroscopic and eclipsing. Consequently, solutions for orbital and stellar parameters make the pair of binaries ideal targets for a study of the colliding winds between two B stars. Chandra ACIS-I observations were obtained to determine X-ray luminosities. AH Cep was detected with an unabsorbed X-ray luminosity at a 90% confidence interval of erg s−1, or , relative to the combined Bolometric luminosities of the two components. While formally …

Limb Darkening And Planetary Transits: Testing Center-To-Limb Intensity Variations And Limb-Darkening Directly From Model Stellar Atmospheres, Hilding R. Neilson, Joseph T. Mcneil, Richard Ignace, John B. Lester

ETSU Faculty Works

The transit method, employed by Microvariability and Oscillation of Stars (MOST), Kepler, and various ground-based surveys has enabled the characterization of extrasolar planets to unprecedented precision. These results are precise enough to begin to measure planet atmosphere composition, planetary oblateness, starspots, and other phenomena at the level of a few hundred parts per million. However, these results depend on our understanding of stellar limb darkening, that is, the intensity distribution across the stellar disk that is sequentially blocked as the planet transits. Typically, stellar limb darkening is assumed to be a simple parameterization with two coefficients that are derived …

On The Binary Nature Of Massive Blue Hypergiants: High-Resolution X-Ray Spectroscopy Suggests That Cyg Ob2 12 Is A Colliding Wind Binary - Iopscience, Lidia M. Oskinova, David P. Huenemoerder, Wolf-Rainer Hamann, Tomer Shenar, A. A.C. Sander, Richard Ignace, H. Todt, R. Hainich

ETSU Faculty Works

The blue hypergiant Cyg OB2 12 (B3Ia+) is a representative member of the class of very massive stars in a poorly understood evolutionary stage. We obtained its high-resolution X-ray spectrum using the Chandra observatory. PoWR model atmospheres were calculated to provide realistic wind opacities and to establish the wind density structure. We find that collisional de-excitation is the dominant mechanism depopulating the metastable upper levels of the forbidden lines of the He-like ions Si xivand Mg xii. Comparison between the model and observations reveals that X-ray emission is produced in a dense plasma, which could reside only at the photosphere …

Revealing The Structure Of The Outer Disks Of Be Stars, Robert Klement, Anthony C. Carciofi, Thomas Rivinius, Lynn D. Matthews, Rodrigo G. Vieira, Richard Ignace, Jon E. Bjorkman, B. C. Mota, Daniel M. Faes, A. D. Bratcher, M. Cure, Stanislav Stefl

ETSU Faculty Works

Context. The structure of the inner parts of Be star disks (≲ 20 stellar radii) is well explained by the viscous decretion disk (VDD) model, which is able to reproduce the observable properties of most of the objects studied so far. The outer parts, on the other hand, are not observationally well-explored, as they are observable only at radio wavelengths. A steepening of the spectral slope somewhere between infrared and radio wavelengths was reported for several Be stars that were previously detected in the radio, but a convincing physical explanation for this trend has not yet been provided.

Aims. We …

On The Absence Of Non-Thermal X-Ray Emission Around Runaway O Stars, Jesus A. Toalá, Lidia M. Oskinova, Richard Ignace

ETSU Faculty Works

Theoretical models predict that the compressed interstellar medium around runaway O stars can produce high-energy non-thermal diffuse emission, in particular, non-thermal X-ray and γ-ray emission. So far, detection of non-thermal X-ray emission was claimed for only one runaway star, AE Aur. We present a search for non-thermal diffuse X-ray emission from bow shocks using archived XMM-Newton observations for a clean sample of six well-determined runaway O stars. We find that none of these objects present diffuse X-ray emission associated with their bow shocks, similarly to previous X-ray studies toward ζ Oph and BD+43°3654. We carefully investigated multi-wavelength observations of …