Analysis of Six Long-period Low-mass Eclipsing Binaries

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Abstract
The radius inflation is predominantly observed in short-period, low-mass stellar systems, while being rarely detected in long-period binaries. Using Transiting Exoplanet Survey Satellite photometric and Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) spectroscopic survey data, we conducted a detailed photometric and spectroscopic analysis of six long-period (P > 7 days) detached eclipsing binaries: TIC 17303250, TIC 196817076, TIC 219488423, TIC 252991035, TIC 344753509, and TIC 72696540. Our results indicate that the first five systems are composed of low-mass stars (M ≤ 0.8M ⊙), while TIC 72696540 is likely composed of subgiant stars with M 1 = 1.267 ± 0.011M ⊙, R 1 = 2.365 ± 0.043R ⊙, and M 2 = 1.281 ± 0.011M ⊙, R 2 = 2.517 ± 0.035R ⊙. Their large radii are solely due to their evolutionary stage. Apart from TIC 72696540, none of the components of these systems displays a clear Li I λ6708 line. Under the assumption of binary rotational synchronization, the rotational velocities of these low-mass stars are found to be less than 8 km s−1, which is the upper limit related to the LAMOST-MRS resolution. Notably, however, significant radius inflation is evident in the systems TIC 17303250, TIC 344753509, and TIC 252991035. Their radii exceed the predictions of the 12 Gyr isochrones. A positive correlation between radius inflation and metallicity is evident in four of the five low-mass stars, with TIC 196817076 being the sole exception. These results suggest that metallicity may play a significant role in causing radius inflation.

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