Multiwaveband photometry of the irradiated brown dwarf WD0137-349B

TL;DR

This study presents multiwaveband photometry of the WD0137-349 binary system, revealing variability and over-luminosity in the brown dwarf's atmosphere likely caused by UV-induced molecular processes.

Contribution

It provides new multiwavelength observations and analyzes the irradiated brown dwarf's atmospheric response, highlighting potential molecular fluorescence effects.

Findings

Brightness peaks at 4.5 microns indicating atmospheric heating.

Observed over-luminosity in Ks and 4.5 micron bands.

Possible H2 fluorescence or H3+ generation due to UV irradiation.

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 Ks in the near-IR and [3.6], [4.5], [5.8] and [8.0] microns 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 Ks and [4.5] micron bands when compared to models of irradiated brown dwarfs with full energy circulation and suggest this over-luminosity may be attributed to H2 fluorescence or H3+ being generated in the atmosphere by the UV irradiation.