Lifetime of starspots on detached eclipsing binaries: Detecting the effects of tides on stellar activity

Abstract

Context. Tidal deformation breaks the axisymmetric structure of stars, and this may affect stellar activity. This effect has been demonstrated in theoretical analyses and simulations, but it lacks observational support. In this paper, we use spot-modulated detached binaries to study the effect of tides on stellar activity. We show this effect by analyzing the properties of the spot lifetime, the harmonic decay timescale, and the orbital parameters. Aims. We aim to explore the differences in spot lifetimes between binaries and single stars, the main mechanisms of spot decay in binaries, and the correlation between orbital parameters and spot lifetimes. These differences will provide clues to the effect of tides on stellar activity. Methods. We collected data of 311 spot-modulated detached binaries and 3272 single stars. The relative orbital parameters of the binaries were derived by combining Kepler photometry, stellar atmospheric parameters from LAMOST DR9 and Gaia DR3, and 2MASS photometry. We then used the ACF method to obtain the rotational periods, lifetimes, and harmonic decay timescales. Finally, we analyzed the correlation between the lifetime of spots and orbital parameters, explored the dominant decay mechanism of spots, and examined the differences in spots for binaries and single stars. Results. The relative lifetime of a starspot is correlated with the sum of the fractional radii, the orbital eccentricity, and the synchronization ratio. Longer lifetimes are observed in close, circular, and synchronous binaries than in the other binaries. The main mechanism for the decay of star spots in binaries is large-scale convective motion. However, on close, cool, and fast-rotating binaries, horizontal diffusion or subphotospheric diffusion are dominant. Compared to single stars, the median lifetime of a starspot on binaries was found to be longer. Moreover, this difference decreases with rotation period. Additionally, it should be noted that spots on binaries experience increased horizontal or subphotospheric diffusion at the same rotation period and effective temperature. Conclusions. According to the observation results, we conclude that the lifetime of starspots on detached close binaries is affected by tidal interactions.