Astronomy and Astrophysics – Astrophysics
Scientific paper
Oct 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009a%26a...505..755r&link_type=abstract
Astronomy and Astrophysics, Volume 505, Issue 2, 2009, pp.755-762
Astronomy and Astrophysics
Astrophysics
7
Techniques: Spectroscopic, Stars: Individual: Tw Hya, Stars: Coronae
Scientific paper
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 Å 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 Å. Due to the absence of line features above 40 Å NH 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 Sc VII and of Ne IX I obtain a value for the electron density of n_e≃ 1012~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 Å better. The emitted X-ray luminosity is in the order of 1030 erg/s.
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