A Reanalysis of the Fundamental Parameters and Age of TRAPPIST-1
We present the distance-calibrated spectral energy distribution (SED) of TRAPPIST-1 using a new medium-resolution (R ∼ 6000) near-infrared (NIR) Folded-port InfraRed Echellette (FIRE) spectrum and its Gaia parallax. We report an updated bolometric luminosity (Lbol) of −3.216 ± 0.016, along with semiempirical fundamental parameters: effective temperature Teff = 2628 ± 42 K, mass = 90 ± 8 MJup, radius = 1.16 ± 0.03 RJup, and log g = 5.21 ± 0.06 dex. Its kinematics point toward an older age, while spectral indices indicate youth; therefore, we compare the overall SED and NIR bands of TRAPPIST-1 to field-age, low-gravity, and low-metallicity dwarfs of similar Teff and Lbol. We find field dwarfs of similar Teff and Lbol best fit the overall and band-by-band features of TRAPPIST-1. Additionally, we present new Allers & Liu spectral indices for the SpeX SXD and FIRE spectra of TRAPPIST-1, both classifying it as intermediate gravity. Examining Teff, Lbol, and absolute JHKW1W2 magnitudes versus optical spectral type places TRAPPIST-1 in an ambiguous location containing both field and intermediate-gravity sources. Kinematics place TRAPPIST-1 within a subpopulation of intermediate-gravity sources lacking bona fide membership in a moving group with higher tangential and UVW velocities. We conclude that TRAPPIST-1 is a field-age source with subtle spectral features reminiscent of a low surface gravity object. To resolve the cause of TRAPPIST-1's intermediate-gravity indicators we speculate on two avenues that might be correlated to inflate the radius: (1) magnetic activity or (2) tidal interactions from planets. We find the M8 dwarf LHS 132 is an excellent match to TRAPPIST-1's spectral peculiarities along with the M9 β dwarf 2MASS J10220489+0200477, the L1 β 2MASS J10224821+5825453, and the L0 β 2MASS J23224684−3133231, which have distinct kinematics, making all four intriguing targets for future exoplanet studies.