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Astron. Astrophys. 350, 571-581 (1999)

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1. Introduction

V 711 Tau (HR 1099, HD 22468) is one of the most active RS CVn non-eclipsing spectroscopic binary systems ([FORMULA]), with a G5-type component of luminosity class V and a cooler K1 IV component. The system is also the primary component of the visual binary system ADS 2644 whose secondary component is a K3 V star. V 711 Tau shows a rich variety of activity phenomena such as dark star-spots (Rodonò et al. 1986, Dorren & Guinan 1982) and highly energetic flares of order of magnitude larger than on the Sun (Linsky et al. 1989). The primary, more massive component of the close binary (the K1 star) shows very strong and variable Ca II H & K, [FORMULA] and ultraviolet emission that are indicative of high chromospheric activity (Rodonò et al. 1987, Neff et al. 1995, Dempsey et al. 1996, Robinson et al. 1996). Furthermore HR 1099 has been observed at radio wavelength (Owen et al. 1976, Trigilio et al. 1993, Umana et al. 1995), at soft X ray (Agrawal & Vaidya 1988), and at EUV wavelengths (Drake et al. 1994). Such high activity is strictly correlated with tidally induced synchronous rotation which makes the magnetic dynamos more efficient. Donati et al. (1990) detected, using Zeeman Doppler Imaging, a [FORMULA] 1000 G magnetic field covering 18% of the K1 star's surface.

In this paper, the chromospheric activity of the active binary system V 711 Tau is studied by applying a Doppler-Imaging technique to Mg II h lines. In Sect. 2 we present the observations and data reduction. The Doppler Imaging technique is described in Sect. 3.1.1. The imaging results for the quiescent and flaring phase are discussed in Sect. 3. The conclusions are drawn in Sect. 4.

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© European Southern Observatory (ESO) 1999

Online publication: October 4, 1999