The Three body system delta Circini

TL;DR

This study investigates the complex three-body system of delta Circini, revealing the presence of a third component, its orbital characteristics, and the potential binary nature of the third body through spectroscopic, photometric, and interferometric data.

Contribution

The paper provides new measurements and analysis of delta Circini's third component, including its possible binary nature and orbital parameters, improving understanding of its apsidal motion and system dynamics.

Findings

Detection of the third component via VLTI with 3.78 mas separation

Indications that the third body may be a binary system

Apsidal-line rotation period estimated at about 141 years

Abstract

Delta Cir is known as an O7.5 III eclipsing and spectroscopic binary with an eccentric orbit. Penny et al. discovered the presence of a third component in the IUE spectra. The eclipsing binary and the third body revolve around a common centre of gravity with a period of 1644 days in an eccentric orbit with the semimajor axis of 10 AU. We demonstrate the presence of the apsidal-line rotation with a period of about 141 years, which is considerably longer than its theoretically predicted value, based on the published radii of the binary components derived from the Hipparchos Hp light curve. However, our new solution of the same light curve resulted in smaller radii and a better agreement between the observed and predicted period of the apsidal- line advance. There are indications that the third body is a binary. The object was resolved by VLTI with the PIONIER combiner; in June 2012 the separation was 3.78 mas, magnitude difference in the H region 1.75 mag. This result means that (assuming the distance 770 pc) the inclination of the long orbit is 87.7 degrees.