EI Eridani, HD26337, a RS CVn-type binary star, Doppler imaged

Data from 11 years of continuous spectroscopic observations of the active RS CVn-type binary star EI Eridani -- gained at NSO/McMath-Pierce, KPNO/Coude Feed and during the MUSICOS 98 campaign -- are reduced and analysed. Thereby, up to 34 Doppler maps in three spectroscopic lines for 32 epochs are obtained, 27 of which are independent of each other. I find that the general morphology of the spot pattern remains persistent for the whole period of 11 years; particularly, no decrease of the polar cap was recognised. However, a high level of activity is noticed in the latitude band of 60 -- 70 degrees where appendages of the polar spot dissolve and emerge prevalently and where active longitudes are identified that migrate with respect to the orbital reference frame. Short-lived low-latitude spots do exist but are much less pronounced.

Three approaches for parameter extraction are introduced and applied to the accumulated heap of Doppler maps: (1) average temperature, separated for several latitude bands; (2) fractional spottedness; and, for analysis of structural temperature distribution, (3) longitudinal and latitudinal spot-occurrence functions. The resulting values do not show a distinct correlation with the proposed activity cycle as seen from photometric long-term observations, thereby suggesting that the photometric activity cycle is not accompanied by a spot cycle as seen on the Sun.

A detailed parameter study is performed. Improved orbital parameters suggest that EI Eri might be complemented by a third component in a wide orbit of about 19 years. Using the Hipparcos parallax, absolute dimensions are derived for the bolometric magnitude, luminosity, radius and inclination of the system. Using evolutionary tracks, EI Eri's position in the HRD is located. It reveals the precise mass and age of the binary components and allows to estimate mass and additional orbital parameters of the proposed tertiary star. Eventually, preliminary differential rotation measurements are carried out, indicating an anti-solar orientation.