New physical elements of HR 7428 and its Hα behaviour^*

¹ Telescopio Nazionale Galileo, Calle Alvarez de Abreu 70, 38700 Santa Cruz de La Palma (TF), Canary Island, Spain
² Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy

Corresponding author: A. Frasca, afr@sunct.ct.astro.it

Received: 7 February 2001
Accepted: 28 May 2001

Abstract

HR 7428 is a spectroscopic binary composed of a K2 II-III and a main-sequence A2 star. Thanks to a new set of radial velocity measurements from our and IUE spectroscopy we have improved the orbital period determination and the spectroscopic elements of both components. Combining optical photometry and UV low dispersion IUE spectra we have determined new stellar parameters through photospheric synthetic spectra using the NextGen models by Hauschildt et al. ([CITE], [CITE]). The hot secondary component parameters agree with those of a typical A2 V star while the radius of the primary cool star turns out to be 40 , i.e. significantly smaller than a previous estimate of 62 . The position of the hot and cool component on the H-R diagram is consistent with a normal evolution, without any mass exchange, of this binary system, whose age is in the range 100-200 Myrs. The system displays a filled-in Hα profile with significant variations both in depth and width along the orbital phase. In addition to the Hα chromospheric emission component, we have detected, at some phases, a broad extra-absorption and emission that we relate to an inter-system cloud.