Low-gravity L Dwarfs Are Likely More Variable

In the Weather on Other Worlds Spitzer Exploration Science program, we surveyed 44 nearby L3-T8 dwarfs for spot-induced rotational variability. Among single L3-L9.5 dwarfs, we found that 80% are variable at >0.2% in the 3-5 μm wavelength range, while 36% of T0-T8 were variable at >0.4%. Taking into account viewing angle and sensitivity considerations, both of these findings are consistent with spots being present on ∼100% of L3-T8 dwarfs. Intriguingly, we find a tentative association (92% confidence) between low surface gravity and high-amplitude variability among L3-L5.5 dwarfs. Although we can not confirm whether lower gravity is also correlated with a higher incidence of variables, the result is promising for the characterization of directly imaged young extrasolar planets through variability.