Is the Algol‐type Eclipsing Binary RX Geminorum a True Triple System?

Abstract

An analysis of the times of minimum light for the long-period Algol-type eclipsing binary RX Gem is presented based on a new linear ephemeris. The curve shows a cyclic oscillation with a period O Ϫ C of 55.7 yr and a semiamplitude of 0.0645 day. Assuming the change to be due to the presence of a "third body" revolving around the RX Gem system, the parameters of the third body's orbit are derived. Since the third-body assumption is in good agreement with the spectroscopic data from several authors and with published photometric solutions (Gaposchkin, Hall, & Walter; Giuricin et al.), RX Gem is likely to be a triple system. In this case, the third body is an A-type star in a circular orbit, which is nearly coplanar to the orbit of the eclipsing pair. However, the recent light-curve analysis by Olson & Etzel does not show any third light, so the third star ( ) M 1 2.41 M 3 , may be an unseen neutron star or black hole. Additional eclipse timings over the next decade will be important to verify the presence of the third body.

The most plausible explanation of the cyclic period changes in close binaries: the case of the RS CVn-type binary WW Dra

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