A Massive White Dwarf or Low-mass Neutron Star Discovered by LAMOST

Abstract We report the discovery of a close binary J0606+2132 (Gaia DR3 3423365496448406272) with P obs = 2.77 days containing a possible massive white dwarf (WD) or a neutron star (NS) using LAMOST spectroscopic data. By a joint fitting of the radial velocity from LAMOST and the light curve from TESS, we derived a circular Keplerian orbit with an inclination of i = 81.°31 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow/> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>7.85</mml:mn> <mml:mo>°</mml:mo> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>6.26</mml:mn> <mml:mo>°</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> , which is consistent with that derived from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>v</mml:mi> <mml:mspace width="0.25em"/> <mml:mi>sin</mml:mi> <mml:mspace width="0.25em"/> <mml:mi>i</mml:mi> </mml:math> . Together with the mass of the visible star, we derived the mass of the invisible object to be <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mn>1.34</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.40</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.35</mml:mn> </mml:mrow> </mml:msubsup> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⊙</mml:mo> </mml:msub> </mml:math> . Spectral disentangling with the LAMOST medium-resolution spectra shows no absorption feature from an additional component, suggesting the presence of a compact object. No X-ray or radio pulsed signal is detected from ROSAT and FAST archive observations. J0606+2132 could evolve into either a Type Ia supernova or an NS through accretion-induced collapse if it is a WD or into an intermediate-mass X-ray binary if it is an NS.