Multiwaveband photometry of the irradiated brown dwarf WD0137−349B

Abstract

WD0137-349 is a white dwarf-brown dwarf binary system in a 116 minute orbit. We present radial velocity observations and multiwaveband photometry from V , R and I in the optical, to J, H and K s in the near-IR and [3.6], [4.5], [5.8] and [8.0] µm in the mid-IR. The photometry and lightcurves show variability in all wavebands, with the amplitude peaking at [4.5] microns, where the system is also brightest. Fluxes and brightness temperatures were computed for the heated and unheated atmosphere of the brown dwarf (WD0137-349B) using synthetic spectra of the white dwarf using model atmosphere simulations. We show that the flux from the brown dwarf dayside is brighter than expected in the K s and [4.5] µm bands when compared to models of irradiated brown dwarfs with full energy circulation and suggest this over-luminosity may be attributed to H 2 fluorescence or H + 3 being generated in the atmosphere by the UV irradiation.

Forward and Inverse Modeling of the Emission and Transmission Spectrum of Gj 436b: Investigating Metal Enrichment, Tidal Heating, and Clouds

“…One obvious suggestion is that there is an additional absorbing molecule that is not included that absorbs in the mid-infrared, particularly in the [4.5] bandpass. The bright [3.6] point could be enhanced by an emission mechanism (e.g., Casewell et al 2015) that operates in that bandpass (but not at [4.5]). Both of these "additional molecule" explanations are speculative and require further study.…”

Atmospheric Electrification in Dusty, Reactive Gases in the Solar System and Beyond

“…However, at 2 lm (K band) and at 4:5 lm, the flux of the brown dwarf is still much brighter than the model predicts. Casewell et al (2015) suggest that UV irradiation can cause photochemical reactions in the upper brown dwarf's atmosphere that produce large hydrocarbon molecules causing the brown dwarf to be brighter at 2 and 4:5 lm as were demonstrated for cosmic ray impact by Rimmer et al (2014).…”

“…Converting the dayside and nightside flux to brightness temperature (peak blackbody temperature with that flux at that wavelength) shows a temperature difference between the two hemispheres of $ 500 K, and a possible temperature inversion in the atmosphere. Casewell et al (2015) compare the observed photometry fluxes (i.e. radiative fluxes measured in a certain wavelength interval) to models of irradiated brown dwarfs and show that the data are best fit by models that incorporate fullenergy circulation around the brown dwarf, but do not contain a temperature inversion.…”

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“…The compact orbits lead to tidally synchronous orbits and significant differences between dayside and nightside brown-dwarf surface temperatures (Casewell et al 2015). Despite the strong irradiation, the dayside temperatures (∼ 3000 K) are still too cool to explain the excesses seen in this region (Casewell et al 2015).…”