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 $\hat{I}º$ And b, a directly-imaged low-mass companion orbiting a nearby B9V star. We detect $\hat{I}º$ 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). $\hat{I}º$ And b's spectrum best resembles that of a low-gravity L0--L1 dwarf (L0--L1${\hat{I}}^3$). Its spectrum and luminosity are very well matched by 2MASSJ0141-4633 and several other 12.5--15 $M_{\mathrm{J}}$ 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${}_{-2}^{+12}$ M${}_{\mathrm{J}}$), and a companion-to-primary mass ratio characteristic of other directly-imaged planets ($q$ $\sim$ 0.005${}_{-0.001}^{+0.005}$). We did not unambiguously identify additional, more closely-orbiting companions brighter and more massive than $\hat{I}º$ And b down to $\ddot{I}$ $\sim$ 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, $\hat{I}º$ And b's semimajor axis is plausibly larger than 75 au and in a region where disk instability could form massive companions. Deeper $\hat{I}º$ 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 $\hat{I}º$ And b's chemistry and whether its spectrum provides an insight into its formation environment.

27 pages, 15 Figures, 6 Tables, 4 Appendices. Accepted for publication in AJ. Provides evidence reestablishing kappa And b as a directly-imaged planet