We present κ Andromeda b’s photometry and astrometry taken with Subaru/SCExAO+HiCIAO and Keck/NIRC2, combined with recently published SCExAO/CHARIS low-resolution spectroscopy and published thermal infrared photometry to further constrain the companion’s atmospheric properties and orbit. κ And b’s Y/Y-K colors are redder than field dwarfs, consistent with its youth and lower gravity. Empirical comparisons of its Y-band photometry and CHARIS spectrum to a large spectral library of isolated field dwarfs reaffirm the conclusion from Currie et al. (2018) that it likely has a low gravity but admit a wider range of most plausible spectral types (L0-L2). Our gravitational classification also suggests that the best-fit objects for κ And b may have lower gravity than those previously reported. Atmospheric models lacking dust/clouds fail to reproduce its entire 1–4.7 µm spectral energy distribution, cloudy atmosphere models with temperatures of ∼ 1700–2000 K better match κ And b data. Most well-fitting model comparisons favor 1700–1900 K, a surface gravity of log(g) ∼ 4–4.5, and a radius of 1.3–1.6 RJup; the best-fit model (DRIFT-Phoenix) yields the coolest and lowest-gravity values: Teff=1700 K and log g=4.0. An update to κ And b’s orbit with ExoSOFT using new astrometry spanning seven years reaffirms its high eccentricity (0.77 ± 0.08). We consider a scenario where unseen companions are responsible for scattering κ And b to a wide separation and high eccentricity. If three planets, including κ And b, were born with coplanar orbits and one of them was ejected by gravitational scattering, a potential inner companion with mass ≳ 10MJup could be located at ≲ 25 au.
|Original language||English (US)|
|State||Published - Nov 21 2019|
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