Abstract
Abstract 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 (L bol) of −3.216 ± 0.016, along with semiempirical fundamental parameters: effective temperature T eff = 2628 ± 42 K, mass = 90 ± 8 M Jup, radius = 1.16 ± 0.03 R Jup, 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 T eff and L bol. We find field dwarfs of similar T eff and L bol 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 T eff, L bol, 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.
Highlights
The majority of stars in our galaxy are low mass, M dwarfs being the most numerous with the longest main sequenceWith numerous searches for exoplanets- such as Kepler and TESS- understanding stellar properties of M dwarfs as ex- GONZALES ET AL.oplanet host stars is extremely pertinent to understanding planet habitability. Kane et al (2016) found 40% of all Kepler planet candidates (1) with radii less than 2 R⊕ and (2) lying within an optimistically-sized habitable zone, orbit stars cooler than 4000 K
In this paper we examine the fundamental parameters of TRAPPIST-1 to determine if it is a typical field M-dwarf host star or if it is more akin to low gravity or subdwarf equivalents
All Folded-port InfraRed Echellette (FIRE) exposures of TRAPPIST-1 obtained on 2017 UT July 27 outside of transit were combined and reduced with the Interactive Data Language (IDL) FireHose v2 package1 (Bochanski et al 2009; Gagné et al 2015), as described in Gagné et al (2015)
Summary
The majority of stars in our galaxy are low mass, M dwarfs being the most numerous with the longest main sequence. Four nearby mid- to late-type M dwarfs with habitable zone planets are: 2MASS J23062928−0502285 (hereafter TRAPPIST-1), Proxima Centauri, LHS 1140, and Teegarden’s Star. Teegarden’s Star, an old magnetically quiet M6.5 dwarf located 3.8 parsecs away, was classified as intermediate gravity by Gagné et al (2015) and hosts two Earth-sized planets both within the conservative habitable zone (Zechmeister et al 2019). In this paper we examine the fundamental parameters of TRAPPIST-1 to determine if it is a typical field M-dwarf host star or if it is more akin to low gravity or subdwarf equivalents. Section presents Allers & Liu (2013) indices and gravity classifications for the entire comparative sample, absolute magnitude and fundamental parameters versus spectral type comparisons, and a comparison of the kinematics of TRAPPIST-1 to β-gravity sources. We present possible reasons for the gravity classification that TRAPPIST-1 receives
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
