Using the Gemini Planet Imager ( GPI ) located at Gemini South , we measured the near-infrared ( 1.0–2.4 \micron ) spectrum of the planetary companion to the nearby , young star \beta Pictoris .
We compare the spectrum obtained with currently published model grids and with known substellar objects and present the best matching models as well as the best matching observed objects .
Comparing the empirical measurement of the bolometric luminosity to evolutionary models , we find a mass of 12.9 \pm 0.2 \mathcal { M } _ { \mathrm { Jup } } , an effective temperature of 1724 \pm 15 K , a radius of 1.46 \pm 0.01 \mathcal { R } _ { \mathrm { Jup } } , and a surface gravity of \log g = 4.18 \pm 0.01 [ dex ] ( cgs ) .
The stated uncertainties are statistical errors only , and do not incorporate any uncertainty on the evolutionary models .
Using atmospheric models , we find an effective temperature of 1700 - 1800 K and a surface gravity of \log g = 3.5 – 4.0 [ dex ] depending upon model .
These values agree well with other publications and with “ hot-start ” predictions from planetary evolution models .
Further , we find that the spectrum of \beta Pic b best matches a low-surface gravity L2 \pm 1 brown dwarf .
Finally comparing the spectrum to field brown dwarfs we find the the spectrum best matches 2MASS J04062677–381210 and 2MASS J03552337+1133437 .