2025AJ....170..252P

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 M₁ = 1.267 ± 0.011M_⊙, R₁ = 2.365 ± 0.043R_⊙, and M₂ = 1.281 ± 0.011M_⊙, R₂ = 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 Iλ6708 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.