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

Raimundo Lopes de Oliveira (1) and Christian Motch (2)

(1) Universidade de São Paulo, IFSC/USP, Brazil; (2) Observatoire Astronomique de Strasbourg, France

We report the discovery of a hard-thermal (T $sim$ 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 $sim$ 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.

Reference: Accepted for publication in ApJL
Status: Manuscript has been accepted

Weblink: http://arxiv.org/abs/1102.4625


Email: rlofilho@gmail.com