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

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 $\sim$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 $0.497\pm 0.005$ and $0.205\pm 0.002$ ${\mathrm{M}}_{\odot }$, and $0.659\pm 0.003$ and $0.424\pm 0.002$ ${\mathrm{R}}_{\odot }$, respectively. With mass and radius uncertainties of $\sim$1 per cent and $\sim$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 $\sim$50 per cent smaller than the dynamical values.

Accepted for publication in MNRAS. 22 pages. Tables 4 and 5 are available in full as ancillary files

References in corpus (14)

• Improving PARSEC models for very low mass stars
• Second ROSAT all-sky survey (2RXS) source catalogue
• The Catalina Surveys Periodic Variable Star Catalog
• An Optical Spectroscopic Study of T Tauri Stars. I. Photospheric Properties
• Evolution of low-mass star and brown dwarf eclipsing binaries
• Older and Colder: The impact of starspots on pre-main sequence stellar evolution
• Magnetic Inhibition of Convection and the Fundamental Properties of Low-Mass Stars. II. Fully Convective Main Sequence Stars
• Empirical Tests of Pre-Main-Sequence Stellar Evolution Models with Eclipsing Binaries
• New low-mass eclipsing binary systems in Praesepe discovered by K2
• The Narrowest M-dwarf Line Profiles and the Rotation-Activity Connection at Very Slow Rotation
• New low-mass members of the Octans stellar association and an updated 30-40 Myr lithium age
• The Fragmentation of Cores and the Initial Binary Population
• Eclipsing binary systems as tests of low-mass stellar evolution theory
• Touchstone Stars: Highlights from the Cool Stars 18 Splinter Session