The red dwarf pair GJ65AB: inflated, spinning twins of Proxima

Abstract

The nearby red dwarf binary GJ65AB (UB+BL Ceti, M5.5Ve+M6Ve) is a cornerstone system to probe the physics of very low mass stars. We present new interferometric measurements of the angular diameters of the two components of GJ65AB with the PIONIER instrument in the H band: thetaUD (A) = 0.558 +/- 0.008 +/- 0.020 mas and thetaUD (B) = 0.539 +/- 0.009 +/- 0.020 mas. They translate into limb-darkened angular diameters of LD (A) = 0.573 +/- 0.021 mas and LD (B) = 0.554 +/- 0.022 mas. From the known parallax, the radii are R(A) = 0.165 +/- 0.006 Rsun and R(B) = 0.159 +/- 0.006 Rsun (sigma(R)/R = 4%). We also observed GJ65AB with the VLT/NACO adaptive optics and refine the orbital parameters and infrared magnitudes of the system. We derive masses for the two components of m(A) = 0.1225 +/- 0.0043 Msun and m(B) = 0.1195 +/- 0.0043 Msun (sigma(m)/m = 4%). To derive the radial and rotational velocities of the two stars, as well as their relative metallicity with respect to Proxima, we also present new individual UVES high resolution spectra. Placing GJ65 A&B in the mass-radius diagram shows that their radii are larger respectively by 14 +/- 4% and 12 +/- 4% compared to expectations from the models by Baraffe et al. (2015). Following Chabrier et al. (2007), we propose that this discrepancy is caused by the inhibition of convective energy transport by a strong internal magnetic field generated by dynamo effect in these two fast rotating stars. A comparison with the almost identical twin but slowly-rotating Proxima strengthens this hypothesis, as the radius of Proxima does not appear inflated compared to models.

12 pages, 10 pages, A&A in press, correction of an error in the Galactic space velocity computation in Table 4

References in corpus (13)

• The Dartmouth Stellar Evolution Database
• New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
• Large-scale magnetic topologies of late M dwarfs
• Evolution of low-mass star and brown dwarf eclipsing binaries
• A White Light Megaflare on the dM4.5e Star YZ CMi
• Reevaluating the Mass-Radius Relation for Low-Mass, Main Sequence Stars
• The VLT/NaCo large program to probe the occurrence of exoplanets and brown dwarfs at wide orbits: II- Survey description, results and performances
• Magnetic Inhibition of Convection and the Fundamental Properties of Low-Mass Stars. II. Fully Convective Main Sequence Stars
• Metallicity of M dwarfs IV. A high-precision [Fe/H] and Teff technique from high-resolution optical spectra for M dwarfs
• Self-Consistent Magnetic Stellar Evolution Models of the Detached, Solar-Type Eclipsing Binary EF Aquarii
• Astrometric and photometric monitoring of GQ Lup and its sub-stellar companion
• Revised age for CM Draconis and WD 1633+572: Toward a resolution of model-observation radius discrepancies
• Transit of Luyten 726-8 within 1 ly from Epsilon Eridani

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