Subhanjoy Mohanty, Keivan G. Stassun
We present high-resolution optical spectra of the young brown-dwarf eclipsing binary 2M0535-05, obtained during eclipse of the higher-mass (primary) brown dwarf. Combined with our previous spectrum of the primary alone (Paper I), the new observations yield the spectrum of the secondary alone. We investigate, through a differential analysis of the two binary components, whether cool surface spots are responsible for suppressing the temperature of the primary. In Paper I, we found a significant discrepancy between the empirical surface gravity of the primary and that inferred via fine analysis of its spectrum. Here we find precisely the {\it same} discrepancy in surface gravity, both qualitatively and quantitatively. While this may again be ascribed to either cool spots or model opacity errors, it implies that cool spots {\it cannot} be responsible for {\it preferentially} lowering the temperature of the primary: if they were, spot effects on the primary spectrum should be preferentially larger, and they are not. The Teff we infer for the primary and secondary, from the TiO-epsilon bands alone, show the same reversal, in the same ratio, as is empirically observed, bolstering the validity of our analysis. In turn, this implies that if suppression of convection by magnetic fields on the primary is the fundamental cause of the Teff reversal, then it cannot be a local suppression yielding spots mainly on the primary (though both components may be equally spotted), but a {\it global} suppression in the interior of the primary. We briefly discuss current theories of how this might work.
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http://arxiv.org/abs/1208.0300
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