Physical Sciences and Mathematics Commons^™

Variability In X-Ray Line Ratios In Helium-Like Ions Of Massive Stars: The Wind-Driven Case, Richard Ignace, Z. Damrau, K. T. Hole

ETSU Faculty Works

Context. High spectral resolution and long exposure times are providing unprecedented levels of data quality of massive stars at X-ray wavelengths.

Aims. A key diagnostic of the X-ray emitting plasma are the fir lines for He-like triplets. In particular, owing to radiative pumping effects, the forbidden-to-intercombination line luminosity ratio, R = f∕i, can be used to determine the proximity of the hot plasma to the UV-bright photospheres of massive stars. Moreover, the era of large observing programs additionally allows for investigation of line variability.

Methods. This contribution is the second to explore how variability in the line …

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 …

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 …

X-Ray Observations Of Bow Shocks Around Runaway O Stars. The Case Of Ζ Oph And Bd+43°3654, Jesus Toala, Lidia M. Oskinova, A. González-Galán, M. A. Guerrero, Richard Ignace, M. Pohl

ETSU Faculty Works

Non-thermal radiation has been predicted within bow shocks around runaway stars by recent theoretical works. We present X-ray observations toward the runaway stars ζ Oph by Chandra and Suzaku and of BD+43°3654 by XMM-Newton to search for the presence of non-thermal X-ray emission. We found no evidence of non-thermal emission spatially coincident with the bow shocks; nonetheless, diffuse emission was detected in the vicinity of ζ Oph. After a careful analysis of its spectral characteristics, we conclude that this emission has a thermal nature with a plasma temperature of T ≈ 2 × 106 K. The cometary shape of this …