Discovery of a Highly Eccentric, Chromospherically Active Binary: ASASSN-V J192114.84+624950.8

TL;DR

This paper reports the discovery and detailed analysis of a highly eccentric, chromospherically active binary star system with unique orbital and stellar properties, identified through an all-sky survey and confirmed with multiple observational methods.

Contribution

It presents the first detailed characterization of a highly eccentric, chromospherically active binary with specific orbital parameters and stellar activity indicators, using combined photometric and spectroscopic data.

Findings

Binary orbit with eccentricity 0.79 and period 18.462 days

Both stars are chromospherically active with distinct rotational periods

Primary star is a late-G or early-K dwarf with specific luminosity and temperature

Abstract

As part of an All-Sky Automated Survey for SuperNovae (ASAS-SN) search for sources with large flux decrements, we discovered a transient where the quiescent, stellar source, ASASSN-V J192114.84+624950.8, rapidly decreased in flux by $\sim55\%$ ($\sim0.9$ mag) in the g-band. The \textit{TESS} light curve revealed that the source is a highly eccentric, eclipsing binary. Fits to the light curve using \textsc{phoebe} find the binary orbit to have $e=0.79$, $P_{\rm orb}=18.462~\text{days}$, and $i=88.6^{\circ}$ and the ratios of the stellar radii and temperatures to be $R_2/R_1 = 0.71$ and $T_{e,2}/T_{e,1} = 0.82$. Both stars are chromospherically active, allowing us to determine their rotational periods of $P_1=1.52$ days and $P_2=1.79$ days, respectively. A LBT/MODS spectrum shows that the primary is a late-G or early-K type dwarf. Fits to the SED show that the luminosities and temperatures of the two stars are $L_1 = 0.48~L_{\sun}$, $T_1= 5050~K$, $L_2 = 0.12~L_{\sun}$, and $T_{2} = 4190~K$. We conclude that ASASSN-V J192114.84+624950.8 consists of two chromospherically active, rotational variable stars in a highly elliptical eclipsing orbit.