Atmospheric Characterization and Further Orbital Modeling of κ Andromeda b

Taichi Uyama, Thayne Currie, Yasunori Hori, Robert J. De Rosa, Kyle Mede, Timothy D. Brandt, Jungmi Kwon, Olivier Guyon, Julien Lozi, Nemanja Jovanovic, Frantz Martinache, Tomoyuki Kudo, Motohide Tamura, N. Jeremy Kasdin, Tyler Groff, Jeffrey Chilcote, Masahiko Hayashi, Michael W. McElwain, Ruben Asensio-Torres, Markus JansonGillian R. Knapp, Eugene Serabyn

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


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. The Y/Y-K colors of κ And b 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. 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 (SED), and 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 R Jup; the best-fit model (Drift-Phoenix) yields the coolest and lowest-gravity values: T eff = 1700 K and log g = 4.0. An update to κ And b's orbit with ExoSOFT using new astrometry spanning 7 yr 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 ≈10 M Jup could be located at ≲25 au.

Original languageEnglish (US)
Article numberab5afa
JournalAstronomical Journal
Issue number2
StatePublished - Feb 2020

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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