Quadruple system HD 135160 in a unique 2+2 configuration

TL;DR

This paper reports the discovery and detailed analysis of a unique quadruple star system, HD 135160, consisting of two binary pairs in a 2+2 configuration, with insights from spectroscopy and space photometry.

Contribution

The study reveals the complex 2+2 quadruple system HD 135160, combining spectroscopic and photometric data to characterize its components and orbital dynamics, which was not previously understood.

Findings

HD 135160 is a 2+2 quadruple system with two binary pairs.

The system includes a 'heartbeat' star with an eccentric 8.234-day orbit.

The other binary has a 5.853-day period with partial eclipses.

Abstract

Analysing a large body of observational data, we found that HD 135160 is a quadruple 2+2 system, composed of a massive ellipsoidal binary ('heartbeat' star) with components Aa and Ab in an eccentric 8.234 d orbit and an eclipsing binary (with components Ba and Bb), with a 5.853 d period and partial eclipses that have already been reported from the space photometry secured by the Transiting Exoplanet Survey Satellite (TESS). Our systematic echelle spectroscopy, secured since September 2021, led to the discovery that the optical spectra are dominated by spectral lines of three early-type stars, two moving around each other on a 8.234 d orbit of a high eccentricity, which causes periodic brightenings near the periastron passage, and the third one (component Ba) being the brighter component of the 5.853 d binary. Both pairs are physically bounded and revolve around each other with a period somewhere between 1600 and 2200 days (4.4 to 6 years). The object exhibits small cyclic light variations of a variable amplitude and characteristic time scale of 0.071 d (14.14 c d-1), seen throughout the whole orbit. The nature of these tiny changes deserves further investigation. It also seems that the earlier classification of the object as a Be star is unfounded.