Unseen companions of V Hya inferred from periodic ejections

Abstract

ABSTRACT A recent study using Hubble Space Telescope observations found periodic, high-speed, collimated ejections (or ‘bullets’) from the star V Hya. The authors of that study proposed a model associating these bullets with the periastron passage of an unseen, substellar companion in an eccentric orbit and with an orbital period of ∼8 yr. Here we propose that V Hya is part of a triple system, with a substellar companion having an orbital period of ∼8 yr, and a tertiary object on a much wider orbit. In this model, the more distant object causes high-eccentricity excitations on the substellar companion’s orbit via the Eccentric Kozai–Lidov mechanism. These eccentricities can reach such high values that they lead to Roche-lobe crossing, producing the observed bullet ejections via a strongly enhanced accretion episode. For example, we find that a ballistic bullet ejection mechanism can be produced by a brown-dwarf-mass companion, while magnetically driven outflows are consistent with a Jovian-mass companion. Finally, we suggest that the distant companion may reside at few a hundred astronomical units on an eccentric orbit.