SCExAO/CHARIS Near-Infrared Direct Imaging, Spectroscopy, and Forward-Modeling of kappa And b: A Likely Young, Low-Gravity Superjovian Companion

Abstract

We present SCExAO/CHARIS high-contrast imaging/\(JHK\) integral field spectroscopy of \(\kappa\) And b, a directly-imaged low-mass companion orbiting a nearby B9V star. We detect \(\kappa\) And b at a high signal-to-noise and extract high precision spectrophotometry using a new forward-modeling algorithm for (A-)LOCI complementary to KLIP-FM developed by Pueyo (2016). \(\kappa\) And b's spectrum best resembles that of a low-gravity L0--L1 dwarf (L0--L1\(\gamma\)). Its spectrum and luminosity are very well matched by 2MASSJ0141-4633 and several other 12.5--15 \(M_{\rm J}\) free floating members of the 40 \(Myr\)-old Tuc-Hor Association, consistent with a system age derived from recent interferometric results for the primary, a companion mass at/near the deuterium-burning limit (13\(^{+12}_{-2}\) M\(_{\rm J}\)), and a companion-to-primary mass ratio characteristic of other directly-imaged planets (\(q\) \(\sim\) 0.005\(^{+0.005}_{-0.001}\)). We did not unambiguously identify additional, more closely-orbiting companions brighter and more massive than \(\kappa\) And b down to \(\rho\) \(\sim\) 0.3" (15 au). SCExAO/CHARIS and complementary Keck/NIRC2 astrometric points reveal clockwise orbital motion. Modeling points towards a likely eccentric orbit: a subset of acceptable orbits include those that are aligned with the star's rotation axis. However, \(\kappa\) And b's semimajor axis is plausibly larger than 75 au and in a region where disk instability could form massive companions. Deeper \(\kappa\) And high-contrast imaging and low-resolution spectroscopy from extreme AO systems like SCExAO/CHARIS and higher resolution spectroscopy from Keck/OSIRIS or, later, IRIS on the Thirty Meter Telescope could help clarify \(\kappa\) And b's chemistry and whether its spectrum provides an insight into its formation environment.