Chandra high-resolution spectra of Apep Plume: Exploring the colliding-wind picture in X-rays

We present results of the first high-resolution observations of the massive Wolf-Rayet (WR) binary Apep Plume, taken with the Chandra High-Energy Transmission Grating in 2023 May. Analysis of these high-quality spectra showed that the spectral lines in this massive binary are broadened (full width at half-maximum, FWHM >= 2400 km s(-1)) and marginally blueshifted (similar to - 150 km s(-1)). A direct modelling of these spectra in the framework of the standard colliding stellar wind (CSW) picture provided a very good correspondence between the shape of the theoretical and observed spectra, but required a mass-loss reduction of 0.42 to be adopted. For a global view on this WR+WR binary, we performed a direct fitting of its optical spectrum by making use of stellar atmosphere models. The corresponding stellar parameters (mass-loss rate and wind velocities) from this analysis were used as input parameters for the CSW modelling of the X-ray emission from Apep Plume.