Planet or Star ?
Brief historical: observers era
Stefan’s Law and effective temperature
Planet in radiative equilibrium
The First Confirmed Brown Dwarf Nakajima et al. (Nature 378, 463, 1995)
The discovery of this first evolved brown dwarf (black curve, Oppenheimer et al.,Science 270, 1478, 1995), confirms model predictions (blue curve, Allard & Hauschildt, ApJ 445, 433, 1995) that brown dwarfs emit more flux between molecular bands at 1.1, 1.3, 1.6 et 2.2 µm than a blackbody would do.
When Stars meet Planets Allard et al. (ARA&A 35, 137, 1997)
AMES-Cond/Dusty 2001 Allard et al. (ApJ 556, 357)
Line formation in brown dwarfs
The observed spectrum of Gl229b (thick black line) is compared to Allard et al. 2001’s Cond model with Teff=1000 K, log g=5.5 (blue dotted line). The model accounts for the opacity contribution of the line wings out to 5000Å from the line centre. Two other are shown where the line opacity is accounted for out to 15000Å from the line centre (green and red lines), one where molecular opacities have been suppressed (red line), to underline the atomic line opacity contributions. One can see that the KI doublet at 7665,7648Å determines the entire emerging spectrum bluewards of about 1 m. The Lorentz profile used in our models is however no longer valid so far from the line centre, and overestimates the far-wing opacity contributions. Hence, when using 15000Å search window around the line centre, our models under-predict the flux peak at 1.25 m by as much as 25%. This stresses the importance of an accurate modelling of the far-wings of alkali lines in brown dwarf atmospheres.
Allard, N. F., Allard, F., et al. A&A 2003
Models obtained with the van der Waals approximation (in blue); and with unified profiles (in magenta) are compared to the observed brown dwarf SDSS1624 spectrum (in black, Teff=1000K, logg=5.5, solar composition).