Fundamental Parameters of a Binary System Consisting of a Red Dwarf and a Compact Star

Xu Ding; KaiFan Ji; ZhiMing Song; NianPing Liu; JianPing Xiong; QiYuan Cheng; ChuanJun Wang; JinLiang Wang; DeQing Wang; ShouSheng He

paper

Fundamental Parameters of a Binary System Consisting of a Red Dwarf and a Compact Star

arXiv:2410.18518

Abstract

TIC 157365951 has been classified as a $δ$ Scuti type by the International Variable Star Index (VSX). Through the spectra from Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) and its light curve, we further discovered that it is a binary system. This binary system comprises a red dwarf star and a compact star. Through the spectral energy distribution (SED) fitting, we determined the mass of the red dwarf star as $M_{1} = 0.31 \pm 0.01 M_{⊙}$ and its radius as $R_{1} = 0.414 \pm 0.004 R_{⊙}$ . By fitting the double-peaked H $α$ emission, we derived the mass ratio of $q = 1.76 \pm 0.04$ , indicating a compact star mass of $M_{2} = 0.54 \pm 0.01 M_{⊙}$ . Using Phoebe to model the light curve and radial velocity curve for the detached binary system, we obtained a red dwarf star mass of $M_{1} = 0.29 \pm 0.02 M_{⊙}$ , a radius of $R_{1} = 0.39 \pm 0.04 R_{⊙}$ , and a Roche-lobe filling factor of $f = 0.995 \pm 0.129$ , which is close to the $f = 1$ expected for a semi-detached system. The Phoebe model gives a compact star mass $M_{2} = 0.53 \pm 0.05 M_{⊙}$ . Constraining the system to be semidetached gives $M_{1} = 0.34 \pm 0.02 M_{⊙}$ , $R_{1} = 0.41 \pm 0.01 R_{⊙}$ , and $M_{2} = 0.62 \pm 0.03 M_{⊙}$ . The consistency of the models is encouraging. The value of the Roche-lobe filling factor suggests that there might be ongoing mass transfer. The compact star mass is as massive as a typical white dwarf.