High-contrast L-band Integral Field Spectroscopy of HD 33632 Ab

TL;DR

This study presents comprehensive spectroscopic analysis of HD 33632 Ab, a directly imaged brown dwarf companion, comparing observations to models and other objects to understand atmospheric cloud processes.

Contribution

First full 1-4 micron spectroscopic analysis of HD 33632 Ab, with detailed model fitting and comparison to similar exoplanets, advancing understanding of cloud effects in substellar atmospheres.

Findings

HD 33632 Ab resembles L8/9 brown dwarfs.

Cloudy atmosphere models fit the data best.

Discrepancies exist between atmospheric and evolutionary model surface gravity estimates.

Abstract

We present LBTI/ALES 3.07-4.08 micron spectroscopic observations of HD~33632~Ab, a ~53 M_Jup directly imaged companion to an F8 star. Spectroscopic measurements of HD 33632 Ab now span 1-4 micron, and we perform the first spectroscopic analysis covering this full range. The data are compared to isolated brown dwarf template spectra, indicating that HD 33632 Ab is similar to L8/9 field brown dwarfs. Synthetic atmosphere model spectra from multiple model families are fit, with cloudy models providing the best fits, consistent with expectations for an L-dwarf. Evolutionary model predictions for the bulk properties of HD 33632 Ab are highly constrained by the precise dynamical mass found for the object. In particular, predictions for surface gravity are narrowly peaked, log(g)=5.21+/-0.05, and not dependent on the effects of clouds or cloud dispersion. We find significant tension between the surface gravities and object radii inferred from atmosphere model fits and those predicted by evolutionary models. We conclude with a comparison to the spectra of the HR 8799 c, d, and e, and emphasize the case that HD 33632 Ab, and other L/T transition directly imaged companions with constrained masses, will serve an essential role in understanding the complex physical processes governing the appearance of clouds in planetary atmospheres.