A potential φ Per-type (Be+sdO) binary: FY CMa

Abstract

The spectrum of the Be star FY CMa is shown to vary periodically with P=37.26±0.03 d. The types of variation, exhibiting transient strong shell phases and a radial-velocity variable He I emission component, suggest the star to be of the same type as φ Per, i.e. having an evolved hot companion ionizing the outer parts of the primary's circumstellar disc where it faces the hot companion. After φ Per and the candidates 59 Cyg and HR 2142, this is only the fourth promising candidate, although such systems should be relatively abundant. The similarities found between φ Per, 59 Cyg, and FY CMa include a radial velocity-variable He I emission feature and a phase-locked V/R cycle. An ephemeris is given that allows a test of the proposed recurrent nature of a strong shell feature observed only in a single spectrum at present.

Based on observations collected at the South African Astronomical Observatory.