The X-ray spectrum of the classical TTauri star TW Hydrae observed by LETGS aboard Chandra

Abstract

Aims. I present the analysis of the X-ray spectrum of the classical TTauri star TW Hydrae, and determine emission measure distributions, elemental abundances, electron temperatures, densities, and line fluxes. Methods. TW Hya was observed in the wavelength range 5–175 A by CHANDRA-LETGS . I performed a multi-temperature fit, based on a collisional ionisation equilibrium (CIE) model for optically thin plasmas. I measured line fluxes by fitting a Gaussian line profile, folded through the response matrix, to the observed line features and I applied these values to establish plasma properties. Results. No line features were established in the spectrum above 40 A. Due to the absence of line features above 40 A N H is calculated to be somewhat higher than assumed so far. The observed “coronal” temperature covers a range from about 1.5 to 20 MK. The abundance pattern shows a very strong enhancement of Ne and some enhancement of N. From forbidden-intercombination line ratios of $\ion{O}{\sc vii}$ and of $\ion{Ne}{\sc ix}$ I obtain a value for the electron density of $n_{\rm e}\simeq 10^{12}~{\rm cm}^{-3}$. This is higher than the value for electron densities in coronal plasmas of older late type main-sequence stars. A blackbody component was added to describe the shape of the continuum around 15 A better. The emitted X-ray luminosity is in the order of 10 30 erg/s.