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Published May 20, 2019 | Published + Submitted
Journal Article Open

No Clear, Direct Evidence for Multiple Protoplanets Orbiting LkCa 15: LkCa 15 bcd are Likely Inner Disk Signals


Two studies utilizing sparse aperture-masking (SAM) interferometry and Hα differential imaging have reported multiple Jovian companions around the young solar-mass star, LkCa 15 (LkCa 15 bcd): the first claimed direct detection of infant, newly formed planets ("protoplanets"). We present new near-infrared direct imaging/spectroscopy from the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system coupled with Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS) integral field spectrograph and multi-epoch thermal infrared imaging from Keck/NIRC2 of LkCa 15 at high Strehl ratios. These data provide the first direct imaging look at the same wavelengths and in the same locations where previous studies identified the LkCa 15 protoplanets, and thus offer the first decisive test of their existence. The data do not reveal these planets. Instead, we resolve extended emission tracing a dust disk with a brightness and location comparable to that claimed for LkCa 15 bcd. Forward-models attributing this signal to orbiting planets are inconsistent with the combined SCExAO/CHARIS and Keck/NIRC2 data. An inner disk provides a more compelling explanation for the SAM detections and perhaps also the claimed Hα detection of LkCa 15 b. We conclude that there is currently no clear, direct evidence for multiple protoplanets orbiting LkCa 15, although the system likely contains at least one unseen Jovian companion. To identify Jovian companions around LkCa 15 from future observations, the inner disk should be detected and its effect modeled, removed, and shown to be distinguishable from planets. Protoplanet candidates identified from similar systems should likewise be clearly distinguished from disk emission through modeling.

Additional Information

© 2019 The American Astronomical Society. Received 2019 February 20; revised 2019 April 18; accepted 2019 April 21; published 2019 May 15. We thank Michiel Min for graciously sharing the MCMax3D code and the Subaru and NASA/Keck Time Allocation Committees for their generous support. We thank the anonymous referee for a careful, thoughtful review. Laurent Pueyo, Jun Hashimoto, Christian Thalmann, Catherine Espaillat, Nienke van der Marel, Hannah Jang-Condell, Geoff Bower, and Scott Kenyon provided helpful comments and/or additional, independent assessments of this manuscript. We emphasize the pivotal cultural role and reverence that the summit of Maunakea has always had within the Hawaiian community. We are most fortunate to conduct scientific observations from this mountain. T.C. was supported by a NASA Senior Postdoctoral Fellowship and NASA/Keck grant LK-2663-948181; L.C. was supported by CONICYT-FONDECYT grant No. 1171246. C.C. acknowledges support from project CONICYT PAI/Concurso Nacional Insercion en la Academia, convocatoria 2015, folio 79150049. M.T. is supported by JSPS KAKENHI grant Nos. 18H05442 and 15H02063. This work utilized the Keck Observatory Archive (KOA), which is operated by the W. M. Keck Observatory and the NASA Exoplanet Science Institute (NExScI), under contract with the National Aeronautics and Space Administration.

Attached Files

Published - Currie_2019_ApJL_877_L3.pdf

Submitted - 1905.04322.pdf


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August 19, 2023
October 20, 2023