SCExAO/CHARIS Near-infrared Direct Imaging, Spectroscopy, and Forward-Modeling of κ And b: A Likely Young, Low-gravity Superjovian Companion
Currie, Thayne; Nielsen, Eric L.; Kwon, Jungmi; Tamura, Motohide; Sitko, Michael; Uyama, Taichi; Martinache, Frantz; Kuzuhara, Masayuki; Schlieder, Joshua; Brandt, Timothy D.; Marois, Christian; Oh, Daehyeon; Akiyama, Eiji; Chilcote, Jeffrey; Guyon, Olivier; Janson, Markus; Jovanovic, Nemanja; Knapp, Gillian R.; Lozi, Julien; Serabyn, Eugene; Blunt, Sarah; Groff, Tyler D.; Skaf, Nour; Nishikawa, Jun; Asensio-Torres, Ruben; Hodapp, Klaus; McElwain, Michael; Grady, Carol; Goebel, Sean; Carson, Joseph; Kasdin, N. Jeremy; Mede, Kyle; Hayashi, Masa
United States, Japan, Canada, France, Sweden, South Korea
Abstract
We present SCExAO/CHARIS high-contrast imaging/JHK integral field spectroscopy of κ And b, a directly imaged low-mass companion orbiting a nearby B9V star. We detect κ And b at a high signal-to-noise ratio and extract high-precision spectrophotometry using a new forward-modeling algorithm for (A-)LOCI complementary to KLIP-FM developed by Pueyo et al. κ And b’s spectrum best resembles that of a low-gravity L0-L1 dwarf (L0-L1γ). Its spectrum and luminosity are very well matched by 2MASS J0141-4633 and several other 12.5-15 M 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 MJ), and a companion-to-primary mass ratio characteristic of other directly imaged planets (q ∼ {0.005}-0.001+0.005). We did not unambiguously identify additional, more closely orbiting companions brighter and more massive than κ And b down to ρ ∼ 0.″3 (15 au). SCExAO/CHARIS and complementary Keck/NIRC2 astrometric points reveal clockwise orbital motion. Modeling points toward a likely eccentric orbit: a subset of acceptable orbits include those that are aligned with the star’s rotation axis. However, κ And b’s semimajor axis is plausibly larger than 55 au and in a region where disk instability could form massive companions. Deeper high-contrast imaging of κ And and low-resolution spectroscopy from extreme adaptive optics systems such as SCExAO/CHARIS and higher-resolution spectroscopy from Keck/OSIRIS or, later, IRIS on the Thirty Meter Telescope could help to clarify κ And b’s chemistry and whether its spectrum provides an insight into its formation environment.