The Hidden Companion in J1527: A 0.69 Solar-mass White Dwarf?

Abstract

Finding nearby neutron stars can probe the supernova and metal-enrichment histories near our solar system. Recently, Lin et al. reported an exciting neutron star candidate, Two Micron All Sky Survey J15274848+3536572 (hereafter J1527), with a small Gaia distance of 118 pc. They claim that J1527 harbors an unseen neutron star candidate with an unusually low mass of 0.98 ± 0.03 M _⊙ . In this work, we use the Canada–France–Hawaii Telescope high-resolution spectrum to measure J1527's orbital inclination independently. Our spectral fitting suggests an orbital inclination of 63° ± 2°. Instead, by fitting a complex hybrid variability model consisting of the ellipsoidal-variation component and the starspot modulation to the observed light curve, Lin et al. obtain an orbital inclination of ${45.2}_{-0.20}^{+0.13}$ degrees. We speculate that the orbital inclination obtained by the light-curve fitting is underestimated since J1527's light curves are obviously not pure ellipsoidal variations. According to our new inclination ( i ∼ 63°), the mass of the unseen compact object is reduced to 0.69 ± 0.02 M _⊙ , which is as massive as a typical white dwarf.

Keywords

• Close binary stars
• Compact objects
• Inclination