Abstract

Long-term period variations of an Algol-type eclipsing binary star, EU Hydrae, are presented based on an analysis of its |$O-C$| curve. As in the cases of other Algols studied in recent papers by one of the authors (S.-B. Qian), an alternate period change has discovered to superimpose on a secular period decrease (⁠|$dP / dt =-4.8 \times 10^{-8} \,\mathrm{d} \,\mathrm{yr}^{-1}$|⁠). By assuming that the alternate variation is cyclic, a period of 26.5 yr and an amplitude of 0.0104 d were determined. A long-term period decrease combined with a semi-detached configuration may indicate that EU Hya is undergoing a secular angular momentum loss. Three possible mechanisms are proposed to explain the alternate period change.

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