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Detection of a Variable Infrared Excess Around SDSS 121209.31+013627.7

J. H. Debes·M. Lopez-Morales·A. Z. Bonanos·A. J. Weinberger
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Abstract

We present near-infrared $JHK_s$ photometry and light curves of the candidate magnetic white dwarf+brown dwarf binary SDSS J121209.31+013627.7 and report on the detection of near-infrared excess and variability in the $K_s-$band. The observed near-infrared excess can be explained by the presence of an L7 brown dwarf and an extra emission source. The $J$ and $H$ light curves appear flat, which rules out eclipses deeper than 0.2 mag and the presence of an accretion hot spot on the white dwarf. From the variable $K_s$ lightcurve, we get a refined period for the system of 88$\pm$1 minutes. We show that the observed variability in $K_s-$band can be explained by cyclotron emission, which can be modeled by a small spot on the surface of the white dwarf. SDSS 1212 exhibits similarities to the ultra-short period polar EF Eridani, however the lack of evidence for Roche-lobe overflow accretion suggests it may be a pre-polar.

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J. H. Debes, M. Lopez-Morales, A. Z. Bonanos, A. J. Weinberger. 2006-07-07. Detection of a Variable Infrared Excess Around SDSS 121209.31+013627.7. https://doi.org/10.1086/507486

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