LAMOST J052016.79+345651.7: An EW-type Binary with Emission Line Spectra and Circumstellar Material

TL;DR

This study characterizes LAMOST J052016.79+345651.7 as an EW-type binary with circumstellar material, emission lines, and evolutionary insights, using multi-band photometry, spectroscopy, and modeling tools.

Contribution

It provides detailed spectroscopic and photometric analysis, revealing circumstellar material, emission line origins, and evolutionary pathways of this binary system.

Findings

Presence of cold circumstellar material indicated by infrared excess.

Detection of Halpha, N II, and S II emission lines from ionized gas.

Evolutionary modeling suggests future evolution into a blue straggler star.

Abstract

LAMOST J052016.79+345651.7 was identified as an EW-type eclipsing binary by Chen et al. when studying the periodic variable stars based on the ZTF telescope. An orbital period of 0.3507818 days has been reported. Using the ZTF g, r, i band light curves, we reproduced the orbital period and obtained a phase folded diagram. The multi-band apparent magnitudes from Pan-STARRS, 2MASS, and WISE, the color indices, and the infrared excess in the WISE w4 band all indicate that LAMOST J0520 contains cold circumstellar material. All 19 LRS from LAMOST exhibit prominent Halpha emission lines, along with clear N II and S II emission lines, indicating that LAMOST J0520 contains optically thin, warm ionized gas with extremely low electron density. From the 19 spectra, an effective temperature of 6200 \pm 400 K can be obtained. Therefore, the emission lines likely originate from shock-driven outflows and mass ejection, while the infrared excess likely comes from dust formed as the outflows cool. We performed light curve fitting and evolutionary simulation study on LAMOST J0520 using PHOEBE and MESA, respectively. The phase shift of the fitted model can be uniquely determined, but the inclination and the fillout_{factor} are degenerate. Considering the angular momentum loss process, the evolutionary simulation from detached binaries to contact binaries can reflect the main evolutionary process of LAMOST J0520. When the orbital period of the evolutionary model is 0.351 days, the other parameters are generally consistent with the observed characteristics of LAMOST J0520. Considering mass loss, LAMOST J052016.79+345651.7 will evolve into a blue straggler star in the future. Future LAMOST medium resolution time-domain spectra of LAMOST J0520 may offer an opportunity to reveal more detailed physical processes.