Apparent Non-Coevality among the Stars in Upper Scorpio: Resolving the Problem using a Model of Magnetic Inhibition of Convection

Abstract

Two eclipsing binaries in the USco association have recently yielded precise values of masses and radii for 4 low-mass members of the association. Standard evolution models would require these dM4.5 - dM5 stars to have ages which are younger than the ages of more massive stars in the association by factors which appear (in extreme cases) to be as large as ~3. Are the stars in the association therefore non-coeval? We suggest that the answer is No: by incorporating the effects of magnetic inhibition of convective onset, we show that the stars in USco can be restored to coevality provided that the 4 low-mass member stars have vertical surface fields in the range 200 - 700 G. Fields of such magnitude have already been measured on the surface of certain solar-type stars in other young clusters.

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• Magnetic Field of the Eclipsing M Dwarf Binary YY Gem
• Magnetic modeling of inflated low-mass stars using interior fields no larger than ~10 kilogauss
• M Dwarf rotation from the $K2$ young clusters to the field. I. A Mass-Rotation Correlation at 10 Myr
• Age spreads and the temperature dependence of age estimates in Upper Sco
• Deep Long Asymmetric Occultation in EPIC 204376071
• Fundamental properties of the pre-main sequence eclipsing stars of MML 53 and the mass of the tertiary
• The Age of the KIC 7177553 System