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

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. 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, ROXS42Bb 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’sbest-estimated temperature is Teff∼1950–2000 K, near the low end of the empirically derived range in Currie et al. 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+3−3MJ, making it one of the lightest planetary-mass objects yet imaged.