X‐Ray Emission from Young Stellar Objects in the ε Chamaeleontis Group: The Herbig Ae Star HD 104237 and Associated Low‐Mass Stars

Abstract

We present Chandra HETGS observations of the Herbig Ae star HD 104237 and the associated young stars comprising lower mass stars, in the 0.15-1.75 -->M? mass range, in their pre-main-sequence phase. The brightest X-ray source in the association is the central system harboring the Herbig Ae primary and a K3 companion. Its X-ray variability indicates modulation possibly on timescales of the rotation period of the Herbig Ae star, and this would imply that the primary significantly contributes to the overall emission. The spectrum of the Herbig Ae+K3 system shows a soft component significantly more pronounced than in other K-type young stars. This soft emission is reminiscent of the unusually soft spectra observed for the single Herbig Ae stars HD 163296 and AB Aur, and therefore we tentatively attribute it to the Herbig Ae of the binary system. The HETGS spectrum shows strong emission lines corresponding to a wide range of plasma temperatures. The He-like triplet of Mg XI and Ne IX suggests the presence of plasma at densities of about 1012 cm?3, possibly indicating an accretion-related X-ray production mechanism. The analysis of the zeroth-order spectra of the other sources indicates X-ray emission characteristics typical of pre-main-sequence stars of similar spectral type, with the exception of the T Tauri HD 104237-D, whose extremely soft emission is very similar to the emission of the classical T Tauri star TW Hya and suggests X-ray production by shocked accreting plasma.