Photometric and spectroscopic observations of the neglected near-contact binary Cl* Melotte 111 AV 1224

Abstract

This paper presents a photometric and spectroscopic study of the short-period binary star Cl*~Melotte~111~AV~1224. Measurements in the $B$, $V$, and $R$ passbands obtained during three observing runs between 2014 and 2017 and medium-resolution spectra secured in 2014, are analyzed together with public data from the SuperWASP and LAMOST projects. Our light curves show marked asymmetry with a variable O'Connell effect. The SuperWASP photometry is used to derive a mean binary period of 0.345225 days. The analysis of the $(O-C)$ diagram reveals that the orbital period is decreasing at a rate of $dP/dt=-3.87\times 10^{-6}$ days yr${}^{-1}$, which may be caused by mass transfer from the more-massive component to the less-massive one. The system is found to be a single-lined spectroscopic binary with a systemic velocity, $\gamma =1\pm 3$ Km s${}^{-1}$, and a semi-amplitude, K${}_1$ = 21 $\pm$ 5 Km s${}^{-1}$. The spectral classification and the effective temperature of the primary component are estimated to be K0V $\pm$ 1 and $5200\pm 150$ K, respectively. The photometric and spectroscopic solutions reveal that Cl*~Melotte~111~AV~1224 is a low-mass ratio ($q=m_2/m_1\sim 0.11$), low-inclination ($\sim 38^{\circ }$) near-contact system. The masses, radii and luminosity for the primary and secondary are estimated to be $1.02\pm 0.06M_{\odot }$, $1.23\pm 0.05R_{\odot }$, $1.01\pm 0.06L_{\odot }$ and $0.11\pm 0.08M_{\odot }$, $0.45\pm 0.05R_{\odot }$, $0.10\pm 0.06L_{\odot }$, respectively. The marginal contact, together with the period decrease, suggests that this binary system may be at a key evolutionary stage, as predicted by the theory of thermal relaxation oscillations.

Accepted for publication in PASP; 11 pages, 11 figures, 8 tables