Three discoveries of gamma Cas analogs from dedicated XMM-Newton observations of Be stars

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 only display 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 gamma Cas (HD44458, HD45995, V558Lyr), bringing the total to 25 known cases, and another gamma Cas candidate (HD120678), bringing the total to 2.

accepted for publication in MNRAS

References in corpus (7)

• Three-dimensional mapping of the local interstellar medium with composite data
• An XMM-Newton view of the young open cluster NGC 6231 -- II. The OB star population
• X-rays from Magnetically Confined Wind Shocks: Effect of Cooling-Regulated Shock Retreat
• A propelling neutron star in the enigmatic Be-star $\gamma$~Cassiopeia
• Discovery of Rapidly Moving Partial X-ray Absorbers within gamma Cassiopeiae
• Is there a propeller neutron star in $\gamma$ Cas?
• pi Aqr is another gamma-Cas object

Cited by in corpus (14)

• Velocity monitoring of gamma-Cas stars reveals their binarity status
• Dynamical masses of the primary Be star and the secondary sdB star in the single-lined binary kappa Dra (B6 IIIe)
• The X-ray emission of Be+stripped star binaries
• Gamma Cas Stars as Be + White Dwarf Binary Systems
• TESS lightcurves of gamma-Cas stars
• The IACOB project VIII. Searching for empirical signatures of binarity in fast-rotating O-type stars
• The X-ray emission of gamma Cassiopeiae during the 2020-2021 disc eruption
• Short-term variability and mass loss in Be stars VI. Frequency groups in $\gamma$ Cas detected by TESS
• Let there be more variability in two gamma Cas stars
• X-ray and optical spectroscopic study of a gamma Cassiopeiae analog source pi Aquarii
• Fluorescent Fe K line emission of gamma Cas stars I. Do gamma Cas stars host propelling neutron stars?
• X-ray emission of massive stars and their winds
• Automated photometry of $\gamma$ Cassiopeiae:the last roundup
• Fluorescent Fe K line emission of gamma Cas stars II. Predictions for magnetic interactions and white-dwarf accretion scenarios