LTD064402+245919, Compact Binary or Subgiant with Red Star Eclipsing 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 ⊙, 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, has shown the depth of one dip increases toward a bluer wavelength, indicating LTD064402+245919 is more likely to be a subgaint 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 ⊙ instead of 2.77 M ⊙, if the refined distance of 5.0 kpc is used. Nevertheless, new multi-color photometry are warranted for the final confirmation of binaries properties.