# EPIC 220204960: A Quadruple Star System Containing Two Strongly Interacting Eclipsing Binaries

## TL;DR

This paper reports the discovery and analysis of a quadruple star system with two strongly interacting eclipsing binaries, providing insights into their orbital dynamics and potential for future observational studies.

## Contribution

It presents the first detailed characterization of a quadruple system with two interacting eclipsing binaries, including orbital parameters and system dynamics.

## Key findings

- Both binaries have orbital periods of ~13.3 and 14.4 days.
- The four stars are similar, each around 0.4 solar masses.
- Outer orbital period likely between 300 and 500 days.

## Abstract

We present a strongly interacting quadruple system associated with the K2 target EPIC 220204960. The K2 target itself is a Kp = 12.7 magnitude star at Teff ~ 6100 K which we designate as "B-N" (blue northerly image). The host of the quadruple system, however, is a Kp = 17 magnitude star with a composite M-star spectrum, which we designate as "R-S" (red southerly image). With a 3.2" separation and similar radial velocities and photometric distances, 'B-N' is likely physically associated with 'R-S', making this a quintuple system, but that is incidental to our main claim of a strongly interacting quadruple system in 'R-S'. The two binaries in 'R-S' have orbital periods of 13.27 d and 14.41 d, respectively, and each has an inclination angle of >89 degrees. From our analysis of radial velocity measurements, and of the photometric lightcurve, we conclude that all four stars are very similar with masses close to 0.4 Msun. Both of the binaries exhibit significant ETVs where those of the primary and secondary eclipses 'diverge' by 0.05 days over the course of the 80-day observations. Via a systematic set of numerical simulations of quadruple systems consisting of two interacting binaries, we conclude that the outer orbital period is very likely to be between 300 and 500 days. If sufficient time is devoted to RV studies of this faint target, the outer orbit should be measurable within a year.