Three discoveries of γ Cas analogues from dedicated XMM-Newton observations of Be stars
Smith, Myron A.; Nazé, Yaël; Torrejón, José M.; Rauw, Gregor; Motch, Christian; Lopes de Oliveira, Raimundo; Robrade, Jan; Kumar, Shami
Belgium, France, Germany, Brazil, United States, Spain
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.