BRITE observations of $\nu$ Centauri and $\gamma$ Lupi, the first non-eclipsing members of the new class of nascent binaries

TL;DR

This study identifies $ u$ Centauri and $\gamma$ Lupi as the first non-eclipsing nascent binary systems with pre-main sequence secondaries, expanding understanding of early binary evolution through combined photometric and spectroscopic analysis.

Contribution

It presents the first detailed analysis of non-eclipsing nascent binaries, revealing their pre-main sequence secondaries and their relation to known eclipsing binary systems.

Findings

Secondary components are pre-MS stars contracting onto the MS.

Both systems exhibit light variations caused by the reflection effect.

The primary stars are early-B main sequence stars.

Abstract

Results of an analysis of the BRITE-Constellation and SMEI photometry and radial-velocity observations, archival and new, of two single-lined spectroscopic binary systems $\nu$ Centauri and $\gamma$ Lupi are reported. In the case of $\gamma$ Lup AB, a visual binary, an examination of the light-time effect shows that component A is the spectroscopic binary. Both $\nu$ Cen and $\gamma$ Lup exhibit light variations with the orbital period. The variations are caused by the reflection effect, i.e. heating of the secondary's hemisphere by the early-B main sequence (MS) primary component's light. The modelling of the light curves augmented with the fundamental parameters of the primary components obtained from the literature photometric data and Hipparcos parallaxes, shows that the secondary components are pre-MS stars, in the process of contracting onto the MS. $\nu$ Cen and $\gamma$ Lup A are thus found to be non-eclipsing counterparts of the B2 IV eclipsing binary (and a $\beta$ Cephei variable) 16 (EN) Lac, the B5 IV eclipsing binary (and an SPB variable) $\mu$ Eri, and the recently discovered LMC nascent eclipsing binaries.