Inspecting Cloudy Substellar Atmospheres with JWST MIRI Synthetic Magnitudes from Spitzer Mid-infrared Spectra

TL;DR

This study uses synthetic JWST MIRI magnitudes derived from Spitzer spectra of ultracool dwarfs to distinguish cloudy from cloud-free atmospheres, highlighting the effectiveness of specific filters in identifying clouds.

Contribution

It demonstrates that JWST MIRI photometry, especially with F770W and F1000W filters, can effectively identify cloudy substellar atmospheres, improving upon current atmospheric models.

Findings

Diagrams with F770W and F1000W best separate cloudy L-type objects.

Objects with mE77ow - mF1000w < 0.03 mag are seven times more likely to be cloudy.

Current models underestimate the 9 um silicate feature, affecting cloud detection accuracy.

Abstract

We examine the positions of substellar objects in mid-infrared color-magnitude and color-color diagrams to distinguish between cloudy and cloud-free atmospheres. Using Spitzer mid-infrared spectra of 113 M5-T9 ultracool dwarfs, we derive synthetic photometry for the JWST MIRI F560W, E'770W, F1000W, and F 1280W filters, which cover key absorption features including the ~9 um silicate signa-ture. We find that diagrams involving F770W and F1000W best separate L-type objects with silicate clouds in their photospheres. L dwarfs with mE77ow - mF1000w < 0.03 mag are seven times more likely to host cloudy atmospheres. Diagrams using F1000W and F1280W are less informative due to the lower signal of the spectra at long wavelengths. Current model predictions struggle to reproduce the positions of cloudy, warm brown dwarfs, likely because atmospheric models underestimate the ~9 um silicate feature. Cloudy Sonora Diamondback models better match the observed trends, although this may reflect improvements capturing indirect effects of clouds on the 6.25 um water absorption feature rather than accurately modeling the silicate feature itself. Our analysis indicates that JWST MIRI photometry can efficiently identify new cloudy extrasolar atmospheres for targeted spectroscopic follow-up, optimizing the use of telescope time.