LAMOST J171013+532646: a detached short-period non-eclipsing hot subdwarf + white dwarf binary

TL;DR

This paper analyzes a nearby, short-period binary system with a hot subdwarf and white dwarf, revealing its properties and evolution, and highlighting its potential as a gravitational wave source.

Contribution

It provides detailed characterization of J1710, including masses, orbital parameters, and evolutionary state, using multi-epoch spectroscopy, photometry, and modeling, which is novel for such a short-period non-eclipsing system.

Findings

Orbital period of 109.2 minutes confirmed by spectroscopy and photometry.

Masses of sdB and WD components determined to be approximately 0.44 and 0.54 solar masses.

System is expected to evolve into a double white dwarf, emitting low-frequency gravitational waves.

Abstract

We present an analysis of LAMOST J171013.211+532646.04 (hereafter J1710), a binary system comprising a hot subdwarf B star (sdB) and a white dwarf (WD) companion. Multi-epoch spectroscopy reveals an orbital period of 109.20279 minutes, consistent with TESS and ZTF photometric data, marking it as the sixth detached system known to harbor a WD companion with a period less than two hours. J1710 is remarkably close to Earth, situated at a distance of only \(350.68^{+4.20}_{-4.21} \, \mathrm{pc}\), with a GAIA G-band magnitude of 12.59, rendering it conducive for continuous observations. The spectral temperature is around 25164 K, in agreement with SED fitting results (\(25301^{+839}_{-743} \, \mathrm{K}\)). The TESS light curve displays ellipsoidal variation and Doppler beaming without eclipsing features. Through fitting the TESS light curve using the Wilson-Devinney code, we determined the masses for the sdB (\(M_1 = 0.44^{+0.06}_{-0.07} \, M_{\odot}\)) and the compact object (\(M_2 = 0.54^{+0.10}_{-0.07} \, M_{\odot}\)), with the compact object likely being a WD. Furthermore, MESA models suggest that the sdB, with a helium core mass of 0.431 \(M_{\odot}\) and a hydrogen envelope mass of \(1.3 \times 10^{-3}\, M_{\odot}\), is in the early helium main-sequence phase. The MESA binary evolution shows that the J1710 system is expected to evolve into a double white dwarf system, making it an important source of low-frequency gravitational waves.