Mapping the Pressure-dependent Day-Night Temperature Contrast of a Strongly Irradiated Atmosphere with HST Spectroscopic Phase Curve

Many brown dwarfs are on ultrashort-period and tidally locked orbits around white dwarf hosts. Because of these small orbital separations, the brown dwarfs are irradiated at levels similar to hot Jupiters. Yet, they are easier to observe than hot Jupiters because white dwarfs are fainter than main-sequence stars at near-infrared wavelengths. Irradiated brown dwarfs are, therefore, ideal hot Jupiter analogs for studying the atmospheric response under strong irradiation and fast rotation. We present the 1.1-1.67 mu m spectroscopic phase curve of the irradiated brown dwarf (SDSS1411-B) in the SDSS J141126.20+ 200911.1 brown dwarf-white dwarf binary with the near-infrared G141 grism of the Hubble Space Telescope Wide Field Camera 3. SDSS1411-B is a 50MJup brown dwarf with an irradiation temperature of 1300 K and has an orbital period of 2.02864 hr. Our best-fit model suggests a phase-curve amplitude of 1.4% and places an upper limit of 11 degrees for the phase offset from the secondary eclipse. After fitting the white dwarf spectrum, we extract the phaseresolved brown dwarf emission spectra. We report a highly wavelength-dependent day-night spectral variation, with a water-band flux variation of about 360%+/- 70% and a comparatively small J-band flux variation of 37%+/- 2%. By combining the atmospheric modeling results and the day-night brightness temperature variations, we derive a pressuredependent temperature contrast. We discuss the difference in the spectral features of SDSS1411-B and hot JupiterWASP43b, as well as the lower-than-predicted day-night temperature contrast of J4111-BD. Our study provides the highprecision observational constraints on the atmospheric structures of an irradiated brown dwarf at different orbital phases.

Automated summary

Brown dwarfs on ultrashort-period orbits around white dwarf hosts provide an ideal opportunity to study atmospheric response under strong irradiation and fast rotation. This study presents high-precision observational constraints on the atmospheric structures of an irradiated brown dwarf at different orbital phases.