Two Young Eclipsing Binaries in Orion with Temperatures and Radii Affected by Spots and Third Bodies

Abstract In this work we present a model of two young eclipsing binaries in the Orion complex. Both heavily spotted, they present radii and temperatures that are in disagreement with the predictions of standard stellar models. 2M05−06 consists of two stars with different masses (∼0.52 and ∼0.42 M ⊙ ) but with very similar radii (∼0.9 R ⊙ ), and with the less massive star having a highly spotted surface that causes it to have a hotter (unspotted) photosphere than the higher-mass star. The other system, 2M05−00, consists of two stars of very similar masses (∼0.34 M ⊙ ), but very different radii (∼0.7 and ∼1.0 R ⊙ ), which creates an appearance of the two eclipsing stars being noncoeval. 2M05−00 appears to have a tertiary companion that could offer an explanation for the unusual properties of the eclipsing stars, as has been seen in some other young triple systems. Comparing the empirically measured properties of these eclipsing binaries to the predictions of stellar models, both standard and magnetic, we find that only the magnetic models correctly predict the observed relationship between mass and effective temperature. However, standard (nonmagnetic) models better predict the temperatures of the unspotted photospheres. These observations represent an important step in improving our understanding of pre-main-sequence stellar evolution and the roles of spots and tertiaries on fundamental stellar properties.