altitude-dependent day-night temperature variation in a strongly irradiated atmosphere

Irradiation and interior heat flux are two important energy sources that shape the thermal structure and drive the atmospheric circulation in planetary atmospheres. Characterizing atmospheres with various energy budgets allow us to conduct comparative studies, identify the key physical and chemical processes in different atmospheres, and advance our understanding of the diverse planetary atmospheres. In my talk, I will present the atmospheric characterization of a rare brown-dwarf white-dwarf binary system SDSS J141126.20+200911.1 (SDSS 1411). In this system, the brown dwarf orbits around the white dwarf with an ultra-short orbital period of two hours — order-of-magnitude shorter than that of typical hot Jupiters. The strong irradiation due to the close orbital distance (0.003au) results in strong day-night temperature variations, which are as high as 250 K in the atmosphere with a T_eff of 1300K! Such a strongly irradiated brown dwarf atmosphere provides a rare opportunity to study the heat redistribution in an atmosphere with significant interior heat flux and irradiation.

In my talk, I will present the HST/WFC3/G141 spectroscopic phase curve of the strongly irradiated brown dwarf SDSS1411-B. Using the optimal spectral extraction method, we obtained a high-precision (SNR ~ 50) and high-cadence (22s per frame) white light curve of the white-dwarf brown-dwarf binary. Based on the orbital-phase resolved emission spectra, we find that the water-band flux variation is about ten times higher than that in the J-band region. I will demonstrate how can we utilize the state-of-the-art atmospheric models and the observed emission spectra to infer the altitude-dependent day-night temperature variations. In addition, I will discuss our interpretation of the observed correlation between the day-night temperature variations and altitudes. I will then compare the results with the analytical theory of day-night circulation and discuss the difference in the emission spectra between the irradiated brown dwarf, isolated brown dwarfs, and hot Jupiters.