Three discoveries of γ Cas analogues from dedicated XMM–Newton observations of Be stars
Yaël Nazé, C. Motch, G. Rauw, Shami Kumar, J. Robrade, Raimundo Lopes de Oliveira, M. A. Smith, J. M. Torrejón
Abstract
ABSTRACT In the last years, a peculiarity of some Be stars – their association with unusually hard and intense X-ray emission – was shown to extend beyond a mere few cases. In this paper, we continue our search for new cases by performing a limited survey of 18 Be stars using XMM–Newton. The targets were selected either on the basis of a previous X-ray detection (exosat,rosat, XMM-slew survey) without spectral information available or because of the presence of a peculiar spectral variability. Only two targets remain undetected in the new observations and three other stars display only faint and soft X-rays. Short-term and/or long-term variations were found in one third of the sample. The spectral characterization of the X-ray brightest 13 stars of the sample led to the discovery of three new γ Cas (HD 44458, HD 45995, and V558 Lyr), bringing the total to 25 known cases, and another γ Cas candidate (HD 120678), bringing the total to two.