On the consistent treatment of the quasi-hydrostatic layers in hot star atmospheres

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Title: On the consistent treatment of the quasi-hydrostatic layers in hot star atmospheres
Authors: Sander, Andreas | Shenar, Tomer | Hainich, Rainer | Giménez García, Ángel | Todt, Helge | Hamann, Wolf-Rainer
Research Group/s: Astronomía y Astrofísica
Center, Department or Service: Universidad de Alicante. Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal
Keywords: Stars: early-type | Stars: mass-loss | Stars: winds, outflows | Stars: atmospheres | Stars: fundamental parameters | Stars: massive
Knowledge Area: Astronomía y Astrofísica
Issue Date: 23-Apr-2015
Publisher: EDP Sciences
Citation: Astronomy & Astrophysics. 2015, 577: A13. doi:10.1051/0004-6361/201425356
Abstract: Context. Spectroscopic analysis remains the most common method to derive masses of massive stars, the most fundamental stellar parameter. While binary orbits and stellar pulsations can provide much sharper constraints on the stellar mass, these methods are only rarely applicable to massive stars. Unfortunately, spectroscopic masses of massive stars heavily depend on the detailed physics of model atmospheres. Aims. We demonstrate the impact of a consistent treatment of the radiative pressure on inferred gravities and spectroscopic masses of massive stars. Specifically, we investigate the contribution of line and continuum transitions to the photospheric radiative pressure. We further explore the effect of model parameters, e.g., abundances, on the deduced spectroscopic mass. Lastly, we compare our results with the plane-parallel TLUSTY code, commonly used for the analysis of massive stars with photospheric spectra. Methods. We calculate a small set of O-star models with the Potsdam Wolf-Rayet (PoWR) code using different approaches for the quasi-hydrostatic part. These models allow us to quantify the effect of accounting for the radiative pressure consistently. We further use PoWR models to show how the Doppler widths of line profiles and abundances of elements such as iron affect the radiative pressure, and, as a consequence, the derived spectroscopic masses. Results. Our study implies that errors on the order of a factor of two in the inferred spectroscopic mass are to be expected when neglecting the contribution of line and continuum transitions to the radiative acceleration in the photosphere. Usage of implausible microturbulent velocities, or the neglect of important opacity sources such as Fe, may result in errors of approximately 50% in the spectroscopic mass. A comparison with TLUSTY model atmospheres reveals a very good agreement with PoWR at the limit of low mass-loss rates.
Sponsor: The first author of this work (A.S.) is supported by the Deutsche Forschungsgemeinschaft (DFG) under grant HA 1455/22. T.S. is grateful for financial support from the Leibniz Graduate School for Quantitative Spectroscopy in Astrophysics, a joint project of the Leibniz Institute for Astrophysics Potsdam (AIP) and the Institute of Physics and Astronomy of the University of Potsdam. A.S. would like to thank the Aspen Center for Physics and the NSF Grant #1066293 for hospitality during the invention and writing of this paper.
URI: http://hdl.handle.net/10045/51050
ISSN: 0004-6361 (Print) | 1432-0746 (Online)
DOI: 10.1051/0004-6361/201425356
Language: eng
Type: info:eu-repo/semantics/article
Rights: © ESO 2015
Peer Review: si
Publisher version: http://dx.doi.org/10.1051/0004-6361/201425356
Appears in Collections:INV - Astronomía y Astrofísica - Artículos de Revistas

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