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arXiv · 2606.26411

A Spitzer Space Telescope Exploration Science Program to Search for Y Dwarf Variability

Michael C. Cushing·Jesica L. Trucks·Kevin K. Hardegree-Ullman·Adam J. Burgasser·Sean J. Carey·Jonathan J. Fortney·Christopher R. Gelino·John E. Gizis·J. Davy Kirkpatrick·Sandy Leggett·Gregory N. Mace·Mark S. Marley·Caroline V. Morley
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Abstract

We present the results of a Spitzer Space Telescope Exploration Science Program to search for and characterize variability in Y dwarfs. We observed 14 Y dwarfs over a 24 hr period at [3.6] and [4.5] and then repeated the observations a few months later. We add two Y dwarfs, WD 0806-661B and WISE J085510.83-071442.5, that were also observed with Spitzer so that our sample includes all Y dwarfs observed for variability with Spitzer. We infer variability fractions of 59%+-15% and 64%+10%-13% for [3.6], and [4.5], in the first epoch, and 35%+17% -11% and 75%+8% -15% in the second epoch. We also find that Y dwarf Spitzer light curves are generally stable over timescales of months, but in some cases can show clear changes in amplitude. Combining our results with a similar Spitzer survey of L and T dwarfs by Metchev et al. (2015), we find the mid-infrared variability fraction of L, T, and Y dwarfs weakly supports the hypothesis that brown dwarf variability is caused by variations in the horizontal and/or vertical structure of condensate clouds.

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Michael C. Cushing, Jesica L. Trucks, Kevin K. Hardegree-Ullman, Adam J. Burgasser, Sean J. Carey, Jonathan J. Fortney, Christopher R. Gelino, John E. Gizis, J. Davy Kirkpatrick, Sandy Leggett, Gregory N. Mace, Mark S. Marley, Caroline V. Morley. 2026-06-24. A Spitzer Space Telescope Exploration Science Program to Search for Y Dwarf Variability. https://arxiv.org/abs/2606.26411

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