LTD064402+245919, compact binary or subgiant with red star eclipsing binary?

TL;DR

This study re-evaluates the nature of binary star system LTD064402+245919, suggesting it is more likely a subgiant with a red star rather than a compact binary, based on multi-wavelength photometry and modeling.

Contribution

The paper provides a revised classification of LTD064402+245919 using new light curves and modeling, challenging previous assumptions of it being a compact binary.

Findings

The secondary star is likely a red M2/3 star with a temperature around 3400 K.

The subgiant's mass is estimated at 1.28 solar masses with a refined distance of 5.0 kpc.

The system is more consistent with a subgiant and red star than a compact binary.

Abstract

Recently, a single-line spectroscopic binary, LTD064402+245919, has been discovered by Yang et al. Using data from LAMOST and ZTF, the unseen companion is estimated to have a mass of 1-3 $M_{\odot}$, orbiting a subgiant with orbital period of 14.50 days, making it a good compact binary candidate without X-ray emission. However, new light curves from ZTF and ASAS-SN, have shown the depth of one dip increases towards a bluer wavelength, indicating LTD064402+245919 is more likely to be a subgiant with a red star. Using both Wilson-Devinney code and Phoebe, the derived $T_{eff}$ of secondary is about 3400 K, corresponding to a red M2/3 star. Additionally, the 20% error of parallax from Gaia is large. The mass of subgiant will be 1.28 $M_{\odot}$ instead of 2.77 $M_{\odot}$, if the refined distance of 5.0kpc is used. Nevertheless, new multi-colour photometry are warranted for the final confirmation of binary properties.