The deep and low-mass-ratio contact binary CSS J022914.4+044340 with a luminous additional companion

Abstract

The first B-, V-, R_c- and I_c-band light curves of CSS J022914.4+044340 are presented and analyzed. It is found that CSS J022914.4+044340 is a low mass ratio (0.198 ± 0.005) deep (63.7 ± 7.9%) contact binary, indicating that it is already at the end evolutionary stage of tidally-locked evolution via magnetized wind. Because of the totally eclipsing character, the photometric solutions are reliable. The temperature and metallicity are determined from the spectroscopic data as T = 5855 ± 15 K and [Fe/H] = -0.842 ± 0.031, respectively. Based on the parallax of Gaia EDR3, the physical parameters of CSS J022914.4+044340 are estimated as ${M}_{1}={1.44}_{-0.22}^{+0.25}{M}_{\odot }$ , ${M}_{2}={0.29}_{-0.05}^{+0.05}{M}_{\odot }$ , ${R}_{1}={1.26}_{-0.06}^{+0.08}{R}_{\odot }$ , ${R}_{2}={0.65}_{-0.04}^{+0.03}{R}_{\odot }$ , ${L}_{1}={1.718}_{-0.191}^{+0.186}{L}_{\odot }$ and ${L}_{2}={0.416}_{-0.050}^{+0.039}{L}_{\odot }$ . Combining the fraction of light from the third body via the photometric solution (54%), the luminosity of the third body is estimated as 2.705 L_⊙. The third body may be inferred to be a subgiant. Thus, why the primary component of CSS J022914.4+044340 has higher mass compared to similar systems is explained, as well as why its metallicity is so poor.