The nearest neutron star candidate in a binary revealed by optical time-domain surveys

The near-Earth(within~100 pc)supernova explosions in the past several million years can cause the global deposition of radioactive elements(e.g.,60Fe)on Earth.The remnants of such supernovae are too old to be easily identified.It is therefore of great interest to search for million-year-old near-Earth neutron stars or black holes,the products of supernovae.However,neutron stars and black holes are challenging to find even in our Solar neighbourhood if they are not radio pulsars or X-ray/γ-ray emitters.Here we report the discovery of one of the nearest(127.7±0.3 pc)neutron star candidates in a detached single-lined spectroscopic binary LAMOST J235456.73+335625.9(hereafter J2354).Utilizing the time-resolved ground-based spectroscopy and space photometry,we find that J2354 hosts an unseen compact object with M_(inv)being 1.4-1.6 M_(⊙).The follow-up Swift ultraviolet(UV)and X-ray observations suggest that the UV and X-ray emission is produced by the visible star rather than the compact object.Hence,J2354 probably harbours a neutron star rather than a hot ultramassive white dwarf.Two-hour exceptionally sensitive radio follow-up observations with Five-hundred-meter Aperture Spherical radio Telescope fail to reveal any pulsating radio signals at the 6σflux upper limit of 12.5μJy.Therefore,the neutron star candidate in J2354 can only be revealed via our time-resolved observations.Interestingly,the distance between J2354 and our Earth can be as close as~50 pc around 2.5 million years(Myrs)ago,as revealed by the Gaia kinematics.Our discovery demonstrates a promising way to unveil the hidden near-Earth neutron stars in binaries by exploring the optical time domain,thereby facilitating understanding of the metal-enrichment history in our Solar neighbourhood.

Erratum to:Compact object candidates with K/M-dwarf companions from LAMOST low-resolution survey[Sci.China-Phys.Mech.Astron.65,229711(2022)]

The paper“Compact object candidates with K/M-dwarf com-panions from LAMOST low-resolution survey”[1]was pub-lished in SCIENCE CHINA Physics,Mechanics&Astronomy(65,229711(2022).doi:10.1007/s11433-021-1809-8).Due to an oversight on our part,some errors were made in the originally published paper.We apologize for these errors and offer the corresponding explanations and corrections for the readers.

Compact object candidates with K/M-dwarf companions from LAMOST low-resolution survey

Searching for compact objects(black holes,neutron stars,or white dwarfs)in the Milky Way is essential for understanding the stellar evolution history,the physics of compact objects,and the structure of our Galaxy.Compact objects in binaries with a luminous stellar companion are perfect targets for optical observations.Candidate compact objects can be achieved by monitoring the radial velocities of the companion star.However,most of the spectroscopic telescopes usually obtain stellar spectra at a relatively low efficiency,which makes a sky survey for millions of stars practically impossible.The efficiency of a large-scale spectroscopic survey,the Large Sky Area Multi-Object Fiber Spectroscopy Telescope(LAMOST),presents a specific opportunity to search for compact object candidates,i.e.,simply from the spectroscopic observations.Late-type K/M stars are the most abundant populations in our Galaxy.Owing to the relatively large Keplerian velocities in the close binaries with a K/M-dwarf companion,a hidden compact object could be discovered and followed-up more easily.In this study,compact object candidates with K/Mdwarf companions are investigated with the LAMOST low-resolution stellar spectra.Based on the LAMOST Data Release 5,we obtained a sample of 56 binaries,each containing a K/M-dwarf with a large radial velocity variation △VR>150 km s^(-1).Complemented with the photometric information from the Transiting Exoplanet Survey Satellite,we derived a sample of 35 compact object candidates,among which,the orbital periods of 16 sources were revealed by the light curves.Considering two sources as examples,we confirmed that a compact object existed in the two systems by fitting the radial velocity curve.This study demonstrates the principle and the power of searching for compact objects through LAMOST.