A CORAVEL radial-velocity monitoring of S stars: symbiotic activity vs. orbital separation

摘要

Orbital elements are presented for the Tc-poor S stars HR 363 (= HD 7351) andHD 191226. With an orbital period of 4592 d (=12.6 y), HR 363 has the longestperiod known among S stars, and yet it is a strong X-ray source. Its X-ray fluxis similar to that of HD 35155, an S star with one of the shortest orbitalperiods (640 d). This surprising result is put in perspective with otherdiagnostics of binary interaction observed in binary S stars. They reveal thatthere is no correlation between the level of binary interaction and the orbitalperiod. This situation may be accounted for if the wind mass-loss rate from thegiant is the principal factor controlling the activity level in these(detached) systems, via a stream of matter funneled through the inner Lagragianpoint.