The quest for companions to post-common envelope binaries: III. A reexamination of HW Virginis

TL;DR

This paper reexamines HW Virginis, proposing a new stable two-companion model with planetary and brown dwarf objects that explains eclipse-time variations through light-travel time effects, supporting the planetary hypothesis.

Contribution

It introduces a new secularly stable two-companion model for HW Virginis that accounts for observed eclipse-time variations without additional processes.

Findings

Proposes a stable two-companion orbit model with periods of 12.7 and 55 years.

Inner companion is a giant planet (~14 M_Jup), outer is a brown dwarf or low-mass star (~30-120 M_Jup).

Model fits eclipse-time data using light-travel time effect alone.

Abstract

We report new mid-eclipse times of the short-period sdB/dM binary HW Vir, which differ substantially from the times predicted by a previous model. The proposed orbits of the two planets in that model are found to be unstable. We present a new secularly stable solution, which involves two companions orbiting HW VIr with periods of 12.7 yr and 55 +/-15 yr. For orbits coplanar with the binary, the inner companion is a giant planet with mass M_3 sin i_3 = 14 M_Jup and the outer one a brown dwarf or low-mass star with a mass of M_4 sin i_4 = 30-120 M_Jup. Using the mercury6 code, we find that such a system would be stable over more than 10^7 yr, in spite of the sizeable interaction. Our model fits the observed eclipse-time variations by the light-travel time effect alone, without invoking any additional process, thereby providing support for the planetary hypothesis of the eclipse-time variations in close binaries. The signature of non-Keplerian orbits may be visible in the data.