Abstract

Exoplanet detections have revolutionized astronomy, offering new insights into solar system architecture and planet demographics. While nearly 1,900 exoplanets have now been discovered and confirmed1, none are still in the process of formation. Transition disks, protoplanetary disks with inner clearings2,3,4 best explained by the influence of accreting planets5, are natural laboratories for the study of planet formation. Some transition disks show evidence for the presence of young planets in the form of disk asymmetries6,7 or infrared sources detected within their clearings, as in the case of LkCa 15 (refs 8, 9). Attempts to observe directly signatures of accretion onto protoplanets have hitherto proven unsuccessful10. Here we report adaptive optics observations of LkCa 15 that probe within the disk clearing. With accurate source positions over multiple epochs spanning 2009–2015, we infer the presence of multiple companions on Keplerian orbits. We directly detect Hα emission from the innermost companion, LkCa 15 b, evincing hot (about 10,000 kelvin) gas falling deep into the potential well of an accreting protoplanet.

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Acknowledgements

This work was supported by NSF AAG grant no. 1211329 and NASA OSS grant NNX14AD20G. This material is based upon work supported by the National Science Foundation under grant no. 1228509. This work was performed in part under contract with the California Institute of Technology (Caltech) funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under grant no. DGE-1143953. Any opinion, findings, and conclusions or recommendations expressed in this material are those of the authors(s) and do not necessarily reflect the views of the National Science Foundation.

Author information

Affiliations

  1. Astronomy Department, University of Arizona, 933 North Cherry Avenue, Tucson, Arizona 85721, USA

    • S. Sallum
    • , K. B. Follette
    • , J. A. Eisner
    • , L. M. Close
    • , P. Hinz
    • , K. Kratter
    • , J. Males
    • , A. Skemer
    • , V. Bailey
    • , D. Defrère
    • , K. Morzinski
    • , E. Spalding
    •  & A. Vaz
  2. Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Stanford, California 94305, USA

    • K. B. Follette
    •  & B. Macintosh
  3. School of Physics, University of Sydney, Sydney, New South Wales 2006, Australia

    • P. Tuthill
  4. Department of Terrestrial Magnetism, Carnegie Institution for Science, 5241 Broad Branch Rd NW, Washington, Washington DC 20015, USA

    • T. Rodigas
    •  & A. J. Weinberger

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Contributions

This work merged two independently acquired and analysed data sets. S.S. led preparation of the manuscript, the orbital fits, and the acquisition and analysis of the LBT data while K.B.F. led the acquisition and analysis of the MagAO data, development of the MagAO SDI pipeline, and drafted MagAO manuscript sections. S.S., K.B.F., J.E., L.C., P.H., A.S., J.M., and K.M. contributed to one or both observing proposals. J.E. modelled circumplanetary disk and hot-start scenarios, developed the NRM mode at LBT, and supervised effort of S.S.; L.C. carried out Hα luminosity calculations and oversaw the MagAO effort. P.H. led LBTI development and support, and helped commission the NRM mode at LBT. K.K. carried out orbital stability analysis. J.M. developed the KLIP code used in MagAO data analysis. P.T. helped develop the NRM mode at LBT. B.M. supervised the effort of K.B.F.; S.S., K.B.F., J.E., L.C., and K.K. contributed key aspects of the manuscript. A.S., V.B., D.D., E.S., and A.V. supported the LBT observations. J.M., K.M., T.R., and A.W. supported the MagAO observations.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to S. Sallum.

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https://doi.org/10.1038/nature15761

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