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A hard and variable X-ray emission from the massive emission line star HD 157832

By Raimundo Lopes de Oliveira and Christian Motch

Abstract

We report the discovery of a hard-thermal (T ~ 130 MK) and variable X-ray emission from the Be star HD 157832, a new member of the puzzling class of gamma-Cas-like Be/X-ray systems. Recent optical spectroscopy reveals the presence of a large/dense circumstellar disc seen at intermediate/high inclination. With a B1.5V spectral type, HD 157832 is the coolest gamma-Cas analog known. In addition, its non detection in the ROSAT all-sky survey shows that its average soft X-ray luminosity varied by a factor larger than ~ 3 over a time interval of 14 yr. These two remarkable features, ``low'' effective temperature and likely high X-ray variability turn HD 157832 into a promising object for understanding the origin of the unusually high temperature X-ray emission in these systems.Comment: Accepted for publication in ApJL; 10 pages, 3 figures, 1 tabl

Topics: Astrophysics - Solar and Stellar Astrophysics
Year: 2011
DOI identifier: 10.1088/2041-8205/731/1/L6
OAI identifier: oai:arXiv.org:1102.4625
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