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Issue A&A Volume 388, Number 3, June IV 2002 Page(s) 889 - 898 Section Formation, structure and evolution of stars DOI 10.1051/0004-6361:20020561

A&A 388, 889-898 (2002)
DOI: 10.1051/0004-6361:20020561

Chromospheric activity on the RS CVn-type binary UX Arietis

S.-h. Gu, H.-s. Tan, H.-g. Shan and F.-h. Zhang

Yunnan Observatory, Joint laboratory for optical astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Kunming, PR China
    e-mail: hgshan@public.km.yn.cn

(Received 20 December 2001 / Accepted 19 March 2002)

Abstract
High resolution spectroscopic observations of UX Ari made during three observing seasons in 2000 have been analyzed by means of the spectral subtraction technique. The information about chromospheric activity of UX Ari has been obtained from several optical chromospheric activity indicators such as the HeI D ₃, NaI D ₁, D ₂, H , and CaII IRT lines. The results suggest the chromospheric activity of the system is associated with the cooler secondary. An orbital phase modulation of chromospheric emissions is found, and consequently the activity longitude area of the system is obtained, that corresponds to the phase interval near the second quadrature of the binary system. A flare-like event is detected during our new observations, characterized by the dramatic increase in the H and CaII IRT emission lines, that is confirmed by the emission of the HeI D ₃ line and the filled-in cores of the NaI D ₁, D ₂ lines. It is found that the values of the EW₈₅₄₂/EW₈₄₉₈ ratio decrease when the activity of the system increases, especially when the flare occurs. The small values of the EW₈₅₄₂/EW₈₄₉₈ ratio indicate that the CaII IRT emissions come from plage-like regions. The high activity level of UX Ari around the quadrature may originate with the coupling between the chromospheric activity of the secondary and the mass transfer activity of the two components.

Key words: stars: activity -- stars: binaries: close -- stars: chromosphere -- stars: flare -- stars: individual: UX Ari

Offprint request: S.-h. Gu, hgshan@public.km.yn.cn

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