A post-common-envelope binary with double-peaked Balmer emission lines from TMTS

¹ Physics Department, Tsinghua University, Beijing 100084, People's Republic of China
² CAS Key Laboratory for Research in Galaxies and Cosmology, Department of Astronomy, University of Science and Technology of China, Hefei, 230026, People's Republic of China
³ School of Astronomy and Space Sciences, University of Science and Technology of China, Hefei 230026, People's Republic of China
⁴ Yunnan Observatories, Chinese Academy of Sciences, Kunming 650216, People's Republic of China
⁵ Key Laboratory for Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, Kunming 650216, People's Republic of China
⁶ International Centre of Supernovae, Yunnan Key Laboratory, Kunming 650216, People's Republic of China
⁷ School of Physics and Astronomy, Beijing Normal University, Beijing 100875, People's Republic of China
⁸ Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University, Beijing 102206, People's Republic of China
⁹ Department of Astronomy, University of California, Berkeley, CA 94720-3411, USA
¹⁰ Beijing Planetarium, Beijing Academy of Science and Technology, Beijing 100044, People's Republic of China
¹¹ CAS Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, People's Republic of China
¹² School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China
¹³ Department of Astronomy, School of Physics, Peking University, Beijing 100871, People's Republic of China
¹⁴ Kavli Institute of Astronomy and Astrophysics, Peking University, Beijing 100871, People's Republic of China

^⋆ Corresponding authors: wang_xf@mail.tsinghua.edu.cn; linjie2019@ustc.edu.cn; wuchengyuan@ynao.ac.cn

Received: 12 January 2025
Accepted: 23 April 2025

Abstract

Context. The dynamical method provides an efficient way to discover post-common-envelope binaries (PCEBs) with faint white dwarfs (WDs), thanks to the development of time-domain survey projects. As close binary systems undergo a common-envelope phase, they offer unique opportunities to study the astrophysical processes associated with binary evolution.

Aims. We perform a comprehensive analysis of the PCEB system TMTS J15530469+4457458 (J1553), discovered by the Tsinghua University-Ma Huateng Telescopes for Survey, to explore its physical origin and evolutionary fate.

Methods. This system is characterized by double-peaked Balmer emission lines, and we applied a cross-correlation function to derive its radial velocity (RV) from a series of phase-resolved Keck spectra. The physical parameters of this binary were obtained by fitting the light curves and RV simultaneously. The locations of the Balmer lines were inferred from Doppler tomography, and a MESA simulation was performed to explore the evolution of this system.

Results. Analyses using the cross-correlation function suggest that this system is a single-lined spectroscopic binary and only one star is optically visible. Further analysis through Doppler tomography indicates that J1553 is a detached binary without an accretion disk. Under such a configuration, the simultaneous light-curve and RV fitting reveal that this system contains an unseen WD with mass M_A = 0.56±0.09 M_⊙, and an M4 dwarf with mass M_B = 0.37±0.02 M_⊙ and radius R_B = 0.403^+0.014_-0.015. The extra prominent Balmer emission lines seen in the spectra can trace the motion of the WD; these lines are likely formed near the WD surface as a result of wind accretion. According to the MESA simulation, J1553 could have evolved from a binary consisting of a 2.0–4.0 M_⊙ zero-age-main-sequence star and an M dwarf with an initial orbital period P_i≈201−476 d, and the system has undergone a common-envelope (CE) phase. After about 3.3×10⁶ yr, J1553 should evolve into a cataclysmic variable, with a transient state as a supersoft X-ray source at the beginning. J1553 is an excellent system for studying wind accretion, CE ejection physics, and binary evolution theory.