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arXiv · 1802.05512

Intriguing X-ray and optical variations of the gamma Cas analog HD45314

G. Rauw·Y. Nazé·M. A. Smith·A. S. Miroshnichenko·J. Guarro Fló·F. Campos·P. Prendergast·S. Danford·J. N. González-Pérez·A. Hempelmann·M. Mittag·J. H. M. M. Schmitt·K. -P. Schröder·S. V. Zharikov
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Abstract

A growing number of Be and Oe stars, named the gamma Cas stars, are known for their unusually hard and intense X-ray emission. This emission could either trace accretion by a compact companion or magnetic interaction between the star and its decretion disk. To test these scenarios, we carried out a detailed optical monitoring of HD45314, the hottest member of the class of gamma Cas stars, along with dedicated X-ray observations on specific dates. High-resolution optical spectra were taken to monitor the emission lines formed in the disk, while X-ray spectroscopy was obtained at epochs when the optical spectrum of the Oe star was displaying peculiar properties. Over the last four years, HD45314 has entered a phase of spectacular variations. The optical emission lines have undergone important morphology and intensity changes including transitions between single- and multiple-peaked emission lines as well as shell events, and phases of (partial) disk dissipation. Photometric variations are found to be anti-correlated with the equivalent width of the H-alpha emission. Whilst the star preserved its hard and bright X-ray emission during the shell phase, the X-ray spectrum during the phase of (partial) disk dissipation was significantly softer and weaker. The observed behaviour of HD45314 suggests a direct association between the level of X-ray emission and the amount of material simultaneously present in the Oe disk as expected in the magnetic star-disk interaction scenario.

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G. Rauw, Y. Nazé, M. A. Smith, A. S. Miroshnichenko, J. Guarro Fló, F. Campos, P. Prendergast, S. Danford, J. N. González-Pérez, A. Hempelmann, M. Mittag, J. H. M. M. Schmitt, K. -P. Schröder, S. V. Zharikov. 2018-02-15. Intriguing X-ray and optical variations of the gamma Cas analog HD45314. https://doi.org/10.1051/0004-6361%2F201731782

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