High-resolution XMM-Newton X-ray spectra of τ SCORPII

Abstract

The first high-resolution X-ray spectra of the B0.2V star τ Scorpii obtained during 22.5ks on Aug. 20, 2001 with the RGS Grating and the epic-mos ccd spectrometers on board XMM-Newton exhibit bright emission lines of the H- and He-like ions of C, N, O, Ne, Mg, and Si, as well as Fe xvii and Fe xviii lines. The emission line and continuum spectra have been simultaneously fitted. We obtain four temperatures: 1.6, 5.2, 8.2, and ≳20 MK, emission measures and abundances. The nitrogen lines are relatively strong: The N/O abundance ratio is ∼3x solar. No indication of a solar-type “FIP effect” was found for the other elements. The temperatures are confirmed by DEM modeling. According to the derived models L x (0.3–10 keV) = 3.2 × 1031 ergs −1 at a distance of 132 pc. The He-like forbidden and intercombination line ratios of N,O,Ne, and Mg are determined by the strong stellar UV radiation field and yield upper limits to the radial distances at which these lines originate. The soft (≲ 8 MK) component probably originates from shocks low in the wind that are produced by the common mechanism of radiation line-driven instabilities, consistent with the observed emission line profiles that are much narrower (≲ 500 km/s) than the broad lines (up to 1500 km/s) observed high up in the wind of ζ Puppis. The hot (∼ 20–40 MK) component is explained by a model involving dense clumps embedded in a wind that approaches high relative velocities (∼ 1400 – 1700 km/s) and the interaction produces strong shocks