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A growing number of Be and Oe stars, named the gamma Cas stars, are known fortheir unusually hard and intense X-ray emission. This emission could eithertrace accretion by a compact companion or magnetic interaction between the starand its decretion disk. To test these scenarios, we carried out a detailedoptical monitoring of HD45314, the hottest member of the class of gamma Casstars, along with dedicated X-ray observations on specific dates.High-resolution optical spectra were taken to monitor the emission lines formedin the disk, while X-ray spectroscopy was obtained at epochs when the opticalspectrum of the Oe star was displaying peculiar properties. Over the last fouryears, HD45314 has entered a phase of spectacular variations. The opticalemission lines have undergone important morphology and intensity changesincluding transitions between single- and multiple-peaked emission lines aswell as shell events, and phases of (partial) disk dissipation. Photometricvariations are found to be anti-correlated with the equivalent width of theH-alpha emission. Whilst the star preserved its hard and bright X-ray emissionduring the shell phase, the X-ray spectrum during the phase of (partial) diskdissipation was significantly softer and weaker. The observed behaviour ofHD45314 suggests a direct association between the level of X-ray emission andthe amount of material simultaneously present in the Oe disk as expected in themagnetic star-disk interaction scenario.

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