Characterization of the gaseous companion κ Andromedae b. New Keck and LBTI high-contrast observations
Kuzuhara, M.; Tamura, M.; Ishii, M.; Kudo, T.; Kandori, R.; Henning, T.; Yamada, T.; Nishimura, T.; Suzuki, R.; Brandner, W.; Homeier, D.; Knapp, G.; Janson, M.; Suto, H.; Bonnefoy, M.; Bailey, V.; Thalmann, C.; Abe, L.; Feldt, M.; Kusakabe, N.; Fukagawa, M.; Allard, F.; Grady, C.; Covey, K. R.; Cumming, A.; Mordasini, C.; Carson, J.; Schlieder, J. E.; Takami, H.; Serabyn, E.; Hayashi, M.; Takami, M.; Biller, B.; Mede, K.; Suenaga, T.; Currie, T.; Hashimoto, J.; Guyon, O.; Hayano, Y.; Iye, M.; Kwon, J.; Matsuo, T.; Morino, J. -I.; Moro-Martin, A.; Takato, N.; Terada, H.; Watanabe, M.; Wisniewski, J.; Usuda, T.; Marleau, G. -D.; Hodapp, K.; Skemer, A.; Klahr, H.; Egner, S.; Pyo, T.; Hauschildt, P.; Skrutskie, M.; Defrère, D.; Tomono, D.; Helling, C.; Witte, S.; Hayashi, S.; Hinz, P.; Marsh Boyer, A. N.; Zimmerman, N.; McElwain, M.; Brandt, T.; Miyama, M.; Takahashi; Turner, E.
Germany, Canada, United States, Netherlands, France, Japan, United Kingdom, Spain, Taiwan
Abstract
Context. We previously reported the direct detection of a low-mass companion at a projected separation of 55 ± 2 AU around the B9-type star κ Andromedae. The properties of the system (mass ratio, separation) make it a benchmark for understanding the formation and evolution of gas giant planets and brown dwarfs on wide orbits.
Aims: We present new angular differential imaging (ADI) images of the system at 2.146 (Ks), 3.776 (L'), 4.052 (NB_4.05), and 4.78 μm (M') obtained with Keck/NIRC2 and LBTI/LMIRCam, as well as more accurate near-infrared photometry of the star with the MIMIR instrument. We aim to determine the near-infrared spectral energy distribution of the companion and use it to characterize the object.
Methods: We used analysis methods adapted to ADI to extract the companion flux. We compared the photometry of the object to reference young, and old objects and to a set of seven PHOENIX-based atmospheric models of cool objects accounting for the formation of dust. We used evolutionary models to derive mass estimates considering a wide range of plausible initial conditions. Finally, we used dedicated formation models to discuss the possible origin of the companion.
Results: We derive a more accurate J = 15.86 ± 0.21, H = 14.95 ± 0.13, Ks = 14.32 ± 0.09 mag for κ And b. We detect the companion in all our high-contrast observations. We confirm previous contrasts obtained at Ks and L' band. We derive NB_4.05 = 13.0 ± 0.2, and M' = 13.3 ± 0.3 mag and estimate log 10(L/L⊙) = -3.76 ± 0.06. Atmospheric models yield Teff = 1900+100-200 K. They do not set any constraint on the surface gravity. "Hot-start" evolutionary models predict masses of 14+25-2 MJup based on the luminosity and temperature estimates, and when considering a conservative age range for the system (30+120-10 Myr), "warm-start" evolutionary tracks constrain the mass to M ≥ 10MJup.
Conclusions: The mass of κ Andromedae b mostly falls in the brown-dwarf regime, owing to remaining uncertainties in age and in mass-luminosity models. According to the formation models, disk instability in a primordial disk may account for the position and a wide range of plausible masses of κ And b.