ZTF J185259.31+124955.2: A new evolved disc-eclipsing binary system

TL;DR

This paper reports the discovery and analysis of ZTF J185259.31+124955.2, a rare long-period eclipsing binary with a disc, showing evolving eclipses and a giant star, indicating rapid post-mass transfer evolution.

Contribution

It presents the identification and detailed characterization of a new evolved disc-eclipsing binary system with unique eclipse properties and spectral features.

Findings

Eclipses occur every 289.57 days with 0.34 magnitude depth.

The system includes an early K-type giant star and a cool component with T_eff < 500 K.

The system is likely in rapid evolution after mass transfer, with a circumstellar disc around an unseen companion.

Abstract

Discs in long-period eclipsing binary systems are rare and can lead to extraordinary eclipsing events. ZTF J185259.31+124955.2 was identified as a candidate disc-eclipsing system through a continuing search programme of ZTF variables with a near-IR excess in the WISE data. Examination of the combined ZTF and ATLAS photometry shows seven eclipses since 2017 with depths of 0\fm34 in all bands on a period of $289.57\pm0.09$\,d. The eclipse width is $\sim 40$\,d but this and the profile evolve over time. Comparison with library spectra shows that the spectral energy distribution from the available photometry is consistent with an early K-type giant, and fitting black-body profiles suggests $T_{eff} \sim 4000$\,K for the stellar component, with a cool component having $T_{eff} < 500$\,K. The reddening and distance, and hence the luminosity place the star within the giant branch. The most likely scenario is that the system is in a state of rapid evolution following Case B/C mass transfer into an extended disc around an unseen companion.