A Reanalysis of the Fundamental Parameters and Age of TRAPPIST-1

Abstract

We present the distance-calibrated spectral energy distribution (SED) of TRAPPIST-1 using a new medium resolution (R~6000) near-infrared FIRE spectrum and its Gaia parallax. We report an updated bolometric luminosity (Lbol) of -3.216+/-0.016, along with semi-empirical fundamental parameters: effective temperature Teff=2628+/-42 K, mass=90+/-8 MJup, radius=1.16+/-0.03 RJup, and logg=5.21+/-0.06 dex. It's kinematics point toward an older age while spectral indices indicate youth therefore, we compare the overall SED and near-infrared 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 2013 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 bonafide 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 two avenues which 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 beta dwarf 2MASS J10220489+0200477, the L1 beta 2MASS J10224821+5825453, and the L0 beta 2MASS J23224684-3133231 which have distinct kinematics making all three intriguing targets for future exoplanet studies.

arXiv comment35 pages, 17 figures, submitted to ApJ 11/2/2018, accepted 9/27/2019

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