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

September 2026 • 2026AJ....172..166C

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

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 −13%+10% for [3.6] and [4.5] in the first epoch, and 35% −11%+17% and 75% −15%+8% 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 S. A. Metchev et al., 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 horizonal and/or vertical structure of condensate clouds.

Links

• PDF https://iopscience.iop.org/article/10.3847/1538-3881/ae8e7c/pdf
• PREPRINT http://arxiv.org/abs/2606.26411
• ELECTR https://doi.org/10.3847/1538-3881/ae8e7c