LAMOST J064137.77+045743.8: A New Binary of an A7-type Pulsating Subgiant and an M-type Red Dwarf
Yanhui Chen, Chaomi Duan, Baokun Sun
TL;DR
This study identifies LAMOST J064137.77+045743.8 as a new binary consisting of an A7-type subgiant primary and an M-type red dwarf companion. It combines spectroscopic analysis from LAMOST LRS/MRS with Gaia astrometry and multi-band photometry (SkyMapper, 2MASS, WISE), plus ZTF time-domain data to establish a pulsating primary and a magnetically active companion, consistent with a long-period, non-eclipsing configuration. The results yield $T_{\rm eff} \sim 7500$ K and $\log g \sim 3.9$ for the primary, evidence for a cool companion in metal lines and IR flux, and multiple pulsation periods with a flare, motivating future asteroseismology of the primary. This work highlights the power of integrating cross-survey data in binary-star characterization and sets the stage for detailed asteroseismic probing of the A7 subgiant.
Abstract
With the progressive release of data from numerous sky surveys, humanity has entered the era of astronomical big data. Multi-wavelength, multi-method research is playing an increasingly crucial role. Binaries account for a substantial fraction of all stellar systems and research into binaries is of fundamental importance. LAMOST J064137.77+045743.8 has not yet been recorded in the SIMBAD astronomical database. We conducted a comprehensive analysis of LAMOST J064137.77+045743.8 using multi-band spectroscopic, astrometric, and photometric data. The low-resolution spectra from Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) suggest that LAMOST J064137.77+045743.8 is a binary consisting of an A7-type subgiant star ($T_{\rm eff}$ $\sim$ 7500\,K and log\,$g$ $\sim$ 3.9) and a cool red dwarf star. Astrometric data from Globe Astrometric Interferometers for Astrophysics support the binary speculation with a Renormalized Unit Weight Error metric value of 1.9. Additional flux observations in the infrared bands further corroborate the presence of a red dwarf companion. The i-band flare detected by the Zwicky Transient Facility (ZTF) photometric observations bolsters the interpretation of an M-type red dwarf companion. The radial velocity variations in the H$α$ lines from LAMOST medium-resolution spectra and the light curves from ZTF both support the classification of the A7 subgiant as a pulsating star. The binary either has a long orbital period, a non-eclipsing binary orbit, or extremely shallow eclipses. Future asteroseismology studies will further probe the internal physics of the A7 subgiants. Research on binaries is incredibly fascinating.