THOR 42: A touchstone ∼24 Myr-old eclipsing binary spanning the fully convective boundary

Murphy, Simon J. and Lawson, Warrick A. and Onken, Christopher A. and Yong, David and Da Costa, Gary S. and Zhou, George ORCID: https://orcid.org/0000-0002-4891-3517 and Mamajek, Eric E. and Bell, Cameron P. M. and Bessell, Michael S. and Feinstein, Adina D. (2019) THOR 42: A touchstone ∼24 Myr-old eclipsing binary spanning the fully convective boundary. Monthly Notices of the Royal Astronomical Society, 491 (4). pp. 4902-4924. ISSN 0035-8711

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Abstract

We present the characterization of CRTS J055255.7-004426 (=THOR 42), a young eclipsing binary comprising two pre-main sequence M dwarfs (combined spectral type M3.5). This nearby (103 pc), short-period (0.859 d) system was recently proposed as a member of the ∼24 Myr-old 32 Orionis Moving Group. Using ground- and space-based photometry in combination with medium- and high-resolution spectroscopy, we model the light and radial velocity curves to derive precise system parameters. The resulting component masses and radii are 0.497 ± 0.005 and 0.205 ± 0.002 {M}_{⊙ }, and 0.659 ± 0.003 and 0.424 ± 0.002 {R}_{⊙ }, respectively. With mass and radius uncertainties of ∼1 per cent and ∼0.5 per cent, respectively, THOR 42 is one of the most precisely characterized pre-main sequence eclipsing binaries known. Its systemic velocity, parallax, proper motion, colour-magnitude diagram placement, and enlarged radii are all consistent with membership in the 32 Ori Group. The system provides a unique opportunity to test pre-main sequence evolutionary models at an age and mass range not well constrained by observation. From the radius and mass measurements we derive ages of 22-26 Myr using standard (non-magnetic) models, in excellent agreement with the age of the group. However, none of the models can simultaneously reproduce the observed mass, radius, temperature, and luminosity of the coeval components. In particular, their H-R diagram ages are 2-4 times younger and we infer masses ∼50 per cent smaller than the dynamical values.


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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Faculty/School / Institute/Centre: No Faculty
Faculty/School / Institute/Centre: No Faculty
Date Deposited: 07 Mar 2022 01:02
Last Modified: 17 Mar 2022 07:26
Uncontrolled Keywords: binaries: eclipsing; binaries: spectroscopic; stars: evolution; stars: fundamental parameters; stars: low mass; stars: pre-main-sequence; Astrophysics - Solar and Stellar Astrophysics; Astrophysics - Earth and Planetary Astrophysics
Fields of Research (2020): 51 PHYSICAL SCIENCES > 5101 Astronomical sciences > 510109 Stellar astronomy and planetary systems
Socio-Economic Objectives (2020): 28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280120 Expanding knowledge in the physical sciences
Identification Number or DOI: https://doi.org/10.1093/mnras/stz3198
URI: http://eprints.usq.edu.au/id/eprint/45014

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