Eclipsing binaries in the open cluster Ruprecht 147. IV: The active triple system EPIC 219511354

TL;DR

This study provides detailed measurements of an active eclipsing binary in Ruprecht 147, revealing larger-than-expected stellar radii and cooler temperatures likely due to stellar activity, and identifies it as a hierarchical triple system.

Contribution

First detailed characterization of the active eclipsing binary EPIC 219511354 in Ruprecht 147, including its triple system nature and comparison with stellar evolution models.

Findings

Measured stellar masses and radii with high precision.

Observed radii larger and temperatures cooler than models predict.

Identified the system as a hierarchical triple with a low-mass tertiary.

Abstract

We report follow-up spectroscopic observations of the 1.62 day, K-type, detached, active, near-circular, double-lined eclipsing binary EPIC 219511354 in the open cluster Ruprecht 147, identified previously on the basis of photometric observations from the Kepler/K2 mission. This is the fourth eclipsing system analyzed in this cluster. A combined analysis of the light curve and radial velocities yields accurate masses of M(Aa) = 0.912 +/- 0.013 MSun and M(Ab) = 0.822 +/- 0.010 MSun for the primary (star Aa) and secondary (Ab), along with radii of R(Aa) = 0.920 +/- 0.016 RSun and R(Ab) = 0.851 +/- 0.016 RSun, and effective temperatures of 5035 +/- 150 and 4690 +/- 130 K, respectively. Comparison with current models of stellar evolution for the known age and metallicity of the cluster reveals that both radii are larger (by 10--14%) and both temperatures cooler (by $\sim$6%) than theoretically predicted, as is often seen in M dwarfs. This is likely caused by the significant stellar activity in the system, manifested here by 6% peak-to-peak out-of-eclipse variability, a filled-in H$\alpha$ line, and its detection as an X-ray source. We also find EPIC 219511354 to be a hierarchical triple system, with a low-mass tertiary in an eccentric 220 day orbit.