EXTRASOLAR STORMS: PRESSURE-DEPENDENT CHANGES IN LIGHT-CURVE PHASE IN BROWN DWARFS FROM SIMULTANEOUS HST AND SPITZER OBSERVATIONS

• Published in: The Astrophysical journal Vol. 826; no. 1; p. 8
• Main Authors: Yang, Hao, Apai, Dániel, Marley, Mark S., Karalidi, Theodora, Flateau, Davin, Showman, Adam P., Metchev, Stanimir, Buenzli, Esther, Radigan, Jacqueline, Artigau, Étienne, Lowrance, Patrick J., Burgasser, Adam J.
• Format: Journal Article
• Language: English
• Published: United States The American Astronomical Society 20.07.2016
• Subjects: Arrays; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ATMOSPHERES; Barometric pressure; Brown dwarf stars; brown dwarfs; CAMERAS; Clouds; COMPARATIVE EVALUATIONS; Flux; infrared: stars; LAYERS; Light levels; MASS; Modulation; PHASE SHIFT; PRESSURE DEPENDENCE; PRESSURE RANGE MEGA PA 10-100; ROTATION; SOLAR WIND; SPACE; SPECTRA; STARS; stars: atmospheres; stars: low-mass; TELESCOPES; VISIBLE RADIATION; WAVELENGTHS
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/0004-637X/826/1/8

ABSTRACT We present Spitzer/Infrared Array Camera Ch1 and Ch2 monitoring of six brown dwarfs during eight different epochs over the course of 20 months. For four brown dwarfs, we also obtained simulataneous Hubble Space Telescope (HST)/WFC3 G141 grism spectra during two epochs and derived light curves in five narrowband filters. Probing different pressure levels in the atmospheres, the multiwavelength light curves of our six targets all exhibit variations, and the shape of the light curves evolves over the timescale of a rotation period, ranging from 1.4 to 13 hr. We compare the shapes of the light curves and estimate the phase shifts between the light curves observed at different wavelengths by comparing the phase of the primary Fourier components. We use state-of-the-art atmosphere models to determine the flux contribution of different pressure layers to the observed flux in each filter. We find that the light curves that probe higher pressures are similar and in phase, but are offset and often different from the light curves that probe lower pressures. The phase differences between the two groups of light curves suggest that the modulations seen at lower and higher pressures may be introduced by different cloud layers.