New Challenges for Wind Shock Models: TheChandraSpectrum of the Hot Star δ Orionis

Abstract

The Chandra spectrum of Ori A shows emission lines from hydrogen-and helium-like states of Si, Mg, Ne, and O, along with N vii Ly and lines from ions in the range Fe xvii-Fe xxi. In contrast to the broad lines seen in Pup and Ori (850 AE 40 and 1000 AE 240 km s À1 half-width at half-maximum [HWHM], respectively), these lines are broadened to only 430 AE 60 km s À1 HWHM. This is much lower than the measured wind terminal velocity of 2000 km s À1. The forbidden, intercombination, and resonance (fir) lines from He-like ions indicate that the majority of the X-ray line emission does not originate at the base of the wind, in agreement with the standard wind shock models for these objects. However, in that model the X-ray emission is distributed throughout an expanding, X-ray-absorbing wind, and it is therefore surprising that the emission lines appear relatively narrow, unshifted, and symmetric. We compare the observed line profiles to recent detailed models for X-ray line profile generation in hot stars, but none of them offers a fully satisfactory explanation for the observed line profiles.

The X-ray spectrum ofδOrionis observed by LETGS aboardChandra

“…The earth's orbital velocity in the direction of δ Ori during the observation and the velocity of δ Ori itself (Wilson 1963) are both about 16 km s −1 , but they have opposite signs and are canceling. The obtained velocities are comparable with those given by Miller et al (2002), based on observations by HETGS. The half widths at half maximum (HWHMs) of the strong lines result in a velocity of about 840 km s −1 , below the terminal velocity of 2000 km s −1 .…”

“…The half widths at half maximum (HWHMs) of the strong lines result in a velocity of about 840 km s −1 , below the terminal velocity of 2000 km s −1 . Our value is higher than the values given by Miller et al (2002), based on HETGS. This might be due to an inconsistency between the instrumental LSFs of LETGS and HETGS.…”

“…(a) Van Leeuwen (2007). (b) Miller et al (2002), taken from Harvin et al (2002). (c) Miller et al (2002), taken from Voels et al (1989).…”

“…(b) Miller et al (2002), taken from Harvin et al (2002). (c) Miller et al (2002), taken from Voels et al (1989). (d) Miller et al (2002), taken from Lamers & Leitherer (1993).…”

“…by Waldron & Cassinelli (2007) and Miller et al (2002) with the Chandra HETGS. They focused on line profiles and line widths, together with ratios of forbidden and intercombination lines in He-like ions.…”