Astron. Astrophys. 362, 683-690 (2000)

Chromospheric two-component NLTE modelling of the binary system V 711 Tau = HR 1099

A.C. Lanzafame ¹, I. Busà ¹ and M. Rodonò <sup>1,2

1</sup> Dipartimento di Fisica e Astronomia, Università di Catania, Viale Andrea Doria 6, 95125 Catania, Italy
² Osservatorio Astrofisico di Catania, Viale Andrea Doria 6, 95125 Catania, Italy

Received 2 March 2000 / Accepted 8 May 2000

Abstract

In this paper we present the first two-component, semi-empirical chromospheric model of the RS CVn binary system V 711 Tau based on detailed fits of H and Mg II h line profiles.

Synthetic H and Mg II h line profiles are computed by means of NLTE radiative transfer calculations. Using the observed Emission Measure distribution to constrain the transition region structure and the photospheric Next-Generation model with =3.5 and 4800 K, we have built a grid of chromospheric models for the K1 IV component of the binary system by means of spline interpolations between photospheric and transition region models. With such interpolations the free parameters are restricted to the temperature minimum and the position of an interpolation knot. We find that a mean single-component model cannot satisfactorily reproduce the observed line profiles. Chromospheric Doppler Imaging is then used to consider the chromospheric emission as due to two different components of known surface coverage and emission. Extensive grids of semi-empirical chromospheric models are built separately for the two components and the weighted-combined synthetic H and Mg II h profiles are compared with observations. Two-component synthetic line profiles reproduce the observed H and Mg II h in detail, indicating that the broad and narrow components can be interpreted in terms of radiative transfer effects in different atmospheric structures for the active and quiet regions. From this analysis we infer information on physical properties of the active region, from which the broad component originates, with respect to the remaining chromosphere from which the narrow component originates. We show also that the variability outside flares can be reproduced considering slightly different models for the active region.

Key words: stars: activity stars: atmospheres line: formation stars: binaries: spectroscopic stars: imaging stars: individual: HR 1099

Send offprint requests to: A.C. Lanzafame

Correspondence to: acl@sunct.ct.astro.it

© European Southern Observatory (ESO) 2000

Online publication: October 24, 2000

helpdesk@link.springer.de