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Published February 2020 | Published + Accepted Version
Journal Article Open

Atmospheric Characterization and Further Orbital Modeling of κ Andromeda b


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.

Additional Information

© 2020 The American Astronomical Society. Received 2019 August 12; revised 2019 November 16; accepted 2019 November 21; published 2020 January 7. The authors would like to thank the anonymous referees for their constructive comments and suggestions to improve the quality of the paper. This paper is based in part on data collected at the Subaru Telescope and obtained from SMOKA, which is operated by the Astronomy Data Center, National Astronomical Observatory of Japan. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The observatory was made possible by the generous financial support of the W. M. Keck Foundation. This work presents results from the European Space Agency (ESA) space mission Gaia. The Gaia data are being processed by the Gaia Data Processing and Analysis Consortium (DPAC). Funding for the DPAC is provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement (MLA). The Gaia mission website is https://www.cosmos.esa.int/gaia. The Gaia archive website is https://archives.esac.esa.int/gaia. T.U. acknowledges a JSPS overseas research fellowship. This work was supported by JSPS KAKENHI grant Nos. JP17J00934, 15H02063, and 18H05442. T.C. was supported by a NASA Senior Postdoctoral Fellowship and NASA/Keck grant LK-2663-948181; R.D.R. was supported by NASA grant NSSC17K0535. The development of SCExAO was supported by JSPS (Grant-in-Aid for Research Nos. 23340051, 26220704, and 23103002), the Astrobiology Center of NINS, Japan, the Mt. Cuba Foundation, and the director's contingency fund at the Subaru Telescope. CHARIS was developed with the support of Grant-in-Aid for Scientific Research on Innovative Areas No. 2302. The authors wish to acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

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Published - Uyama_2020_AJ_159_40.pdf

Accepted Version - 1911.09758.pdf


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