X-ray response to disk evolution in two gamma-Cas stars

The HU emission of a set of southern W Cas stars was monitored since 2019, with the aim of detecting transition events and examining how their peculiar X-ray emission would react in such cases. Two stars, HD 119682 and V767 Cen, were found to display slowly decreasing disk emissions. These decreases were not perfectly monotonic and several temporary and limited re-building events were observed. For HD 119682, the emission component in HU disappeared in mid-July 2020. In X-rays, the X-ray flux was twice smaller than recorded two decades ago but of a similar level as observed a decade ago. The X-ray flux decreased over the campaign by 30%, but the hardness remained similar in datasets of all epochs. In particular, the W Cas character remained as clear as before even when there was no trace of disk emission in the HU line. For V767 Cen, the full disappearance of disk emission in HU never occurred. We followed closely a disk rebuilding event, but no significant change in flux or hardness was detected. These behaviours are compared to those of other W Cas stars and their consequences on the X-ray generation are discussed.