2008/06/13 by F. Favata, C. Neiner, P. Testa +5 · 3 citations
Physics and Astronomy · #Amplitude #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #EPIC #Light curve #Modulation (music) #Nuclear physics #Optics #Phase (matter) #Physics #Plasma #Solar and Space Plasma Dynamics #Spectral line #Spectral resolution #Spectrograph #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1051/0004-6361:20078529
Accepted for publication in Astronomy & Astrophysics
arxiv created 2008/06/13 · openalex publication_date 2008/10/27 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
<i>Aims. <i/>We have performed a set of high- and low-spectral resolution phase-resolved X-ray observations of the magnetic B star <i>β<i/> Cep, for which theoretical models predict the presence of a confined wind emitting X-rays from stationary shocks. Given the peculiar geometry of <i>β<i/> Cep, some of the models predict strong rotational modulation of the X-ray emission, while other models predict a much lower amplitude modulation at 90 deg phase shift from the modulation predicted from the first group of models. Our observations were designed to provide a stringent test of such models.<i>Methods. <i/>We obtained four observations spaced in rotational phase with XMM-<i>Newton<i/> (using both the EPIC cameras and the RGS spectrograph) and with <i>Chandra<i/> (using the LETG spectrograph). A detailed analysis of the data was performed to derive both photometric and spectral parameters from the EPIC data, searching for rotational modulation, and to derive the location of the X-ray plasma from the line ratios in the He-like triplets of N, O, and Ne from the RGS data. The LETG data were used to constrain the presence of bulk motions in the plasma. <i>Results. <i/>The strong rotational modulation predicted by the early, static magnetically-confined wind model for the X-ray emission is not observed in <i>β<i/> Cep. The small modulation present goes in the opposite direction, pointing to the absence of any optically thick disk of neutral material, and showing a modulation consistent with the later, dynamic models of magnetically-confined wind models in B stars. The lack of observed bulk motion points to the plasma being confined by a magnetic field, but the low plasma temperature and lack of any flaring show that the plasma is not heated by magnetic reconnection. Therefore, the observations point to X-ray emission from shocks in a magnetically confined wind, with no evidence of an optically thick, dense disk at the magnetic equator.