Light curve modeling of the nearest neutron star candidate LAMOST J235456.73+335625.9

Abstract

The discovery of heavy radioactive elements (e.g., $^{60}\mathrm{Fe}$) on Earth suggests that supernova explosions may have occurred near our planet within the past million years, potentially having a significant impact on the ecological environment. This finding has motivated the search for nearby neutron stars in the Solar neighborhood. In a recent study, a candidate for one of the closest neutron stars to Earth, LAMOST J235456.73+335625.9 (hereafter J2354), was reported. Based on dynamical mass measurements under different inclination angle assumptions, the inferred mass range for the unseen compact companion in the system is $1.4$--$1.6$ $M_{\odot}$. Hence, the unseen companion in J2354 is either a massive cold white dwarf or a neutron star. Here we model the flux variations of J2354 as a combination of ellipsoidal modulation and surface spots. We test both cold spot and hot spot models, setting the number of spots to two in each case, and constrain the spot properties through light curve fitting. In the cold spot scenario, the spots are mostly visible at phases $0.5$--$0.75$, whereas in the hot spot scenario, the spots appear predominantly at phases $0.25$--$0.5$. The hot spot model shows better agreement with the observed H$α$ phase variation than the cold spot model. Furthermore, the thermal radiation of a massive but cold white dwarf cannot produce the level of localized heating required to explain the hot spot unless additional heating mechanisms are involved; in contrast, a neutron star can naturally provide such heating through energetic winds. Our results are consistent with the neutron star interpretation of the compact object in J2354.