ROXs 42Bb is a Very Light, Fluffy Exoplanet at 9 Jupiter Masses

A First-Look Atmospheric Modeling Study of the Young Directly-Imaged Planet-Mass Companion, ROXs 42Bb

Authors:

Currie et al

Abstract:

We present and analyze JKsL′ photometry and our previously published H-band photometry and K-band spectroscopy for ROXs 42Bb, an object Currie et al. (2014) first reported as a young directly imaged planet-mass companion. ROXs 42Bb exhibits IR colors redder than field L dwarfs but consistent with other planet-mass companions. From the H2O-2 spectral index, we estimate a spectral type of L0 ± 1; weak detections/non-detections of the CO bandheads, NaI, and CaI support evidence for a young, low surface gravity object primarily derived from the H2(K) index. ROXs 42Bb's photometry/K-band spectrum are inconsistent with limiting cases of dust-free atmospheres (COND) and marginally inconsistent with the AMES/DUSTY models and the BT-SETTL models. However, ROXS 42Bb data are simultaneously fit by atmosphere models incorporating several micron-sized dust grains entrained in thick clouds, although further modifications are needed to better reproduce the K-band spectral shape. ROXs 42Bb's best-estimated temperature is Teff ∼ 1950--2000 K, near the low end of the empirically-derived range in Currie et al. (2014). For an age of ∼ 1--3 Myr and considering the lifetime of the protostar phase, ROXs 42Bb's luminosity of log(L/L⊙) ∼ -3.07 ± 0.07 implies a mass of 9+3−3 MJ, making it one of the lightest planetary mass objects yet imaged.