A giant planet undergoing extreme-ultraviolet irradiation by its hot massive-star host
Abstract
The amount of ultraviolet irradiation and ablation experienced by a planet depends strongly on the temperature of its host star. Of the thousands of extrasolar planets now known, only six have been found that transit hot, A-type stars (with temperatures of 7,300–10,000 kelvin), and no planets are known to transit the even hotter B-type stars. For example, WASP-33 is an A-type star with a temperature of about 7,430 kelvin, which hosts the hottest known transiting planet, WASP-33b (ref. 1); the planet is itself as hot as a red dwarf star of type M (ref. 2). WASP-33b displays a large heat differential between its dayside and nightside, and is highly inflated–traits that have been linked to high insolation. However, even at the temperature of its dayside, its atmosphere probably resembles the molecule-dominated atmospheres of other planets and, given the level of ultraviolet irradiation it experiences, its atmosphere is unlikely to be substantially ablated over the lifetime of its star. Here we report observations of the bright star HD 195689 (also known as KELT-9), which reveal a close-in (orbital period of about 1.48 days) transiting giant planet, KELT-9b. At approximately 10,170 kelvin, the host star is at the dividing line between stars of type A and B, and we measure the dayside temperature of KELT-9b to be about 4,600 kelvin. This is as hot as stars of stellar type K4 (ref. 5). The molecules in K stars are entirely dissociated, and so the primary sources of opacity in the dayside atmosphere of KELT-9b are probably atomic metals. Furthermore, KELT-9b receives 700 times more extreme-ultraviolet radiation (that is, with wavelengths shorter than 91.2 nanometres) than WASP-33b, leading to a predicted range of mass-loss rates that could leave the planet largely stripped of its envelope during the main-sequence lifetime of the host star.
Additional Information
© 2017 Macmillan Publishers Limited, part of Springer Nature. Received 02 February 2017; Accepted 19 April 2017; Published online 05 June 2017. This research was made possible by the KELT survey, the KELT Follow-Up Network, and support from The Ohio State University, Vanderbilt University and Lehigh University. Work by B.S.G. and D.J.S. was partially supported by NSF CAREER grant AST-1056524. K.G.S. and K.A.C. acknowledge partial support from NSF PAARE grant AST-1358862. B.S.G. acknowledges support by the Jet Propulsion Laboratory, operated by the California Institute of Technology, and the Exoplanet Exploration Program of the National Aeronautics and Space Administration (NASA). B.J.F. notes that this material is based upon work supported by the National Science Foundation Graduate Research Fellowship under grant no. 2014184874. 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. Work performed by J.E.R. was supported by the Harvard Future Faculty Leaders Postdoctoral fellowship. K.K.M. acknowledges the purchase of SDSS filters for Whitin Observatory by the Theodore Dunham Jr Grant of the Fund for Astronomical Research. N.N. acknowledges support by the Japan Society for Promotion of Science (JSPS) KAKENHI Grant Number JP25247026. We acknowledge observations by M. Kunitomo, R. Hasegawa, B. Sato, H. Harakawa, T. Hirano and H. Izumiura on the Okayama 188 cm telescope (HIDES observations) and N. Kusakabe, M. Onitsuka and T. Ryu for MuSCAT observations. The NIRC2 AO data in this work were obtained at the W.M. Keck Observatory, which was financed by the W.M. Keck Foundation and is operated as a scientific partnership between the California Institute of Technology, the University of California and NASA. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. This work has made use of NASA's Astrophysics Data System, the Exoplanets Data Explorer at exoplanets.org, the Extrasolar Planet Encyclopedia at exoplanet.eu, the SIMBAD database operated at CDS, Strasbourg, France, and the VizieR catalogue access tool, CDS, Strasbourg, France. This publication makes use of data products from the Widefield Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles; the Jet Propulsion Laboratory/California Institute of Technology, which is funded by NASA; the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by NASA; and the American Association of Variable Star Observers (AAVSO) Photometric All-Sky Survey (APASS), whose funding is provided by the Robert Martin Ayers Sciences Fund and the AAVSO Endowment (https://www.aavso.org/aavso-photometric-all-sky-survey-data-release-1). We acknowledge input from T. Barman, J. Fortney, M. Marley and K. Zanhle. Author Contributions: B.S.G. led the process from initial candidate selection to final planet confirmation. B.S.G. and K.G.S. wrote the majority of the main manuscript and contributed to the analysis of the results. K.A.C. principally coordinated the assemblage of the final results and production of the Methods. T.G.B. and G.Z. led the Doppler tomographic analysis, and also contributed to the final modelling and interpretation. J.D.E., R.J.S., D.J.S., L.A.B., J.P., J.E.R., K.D.C., M.C.J. and M.P. all provided critical insight, analysis or interpretation of the system. G.D., V.B., S.C.N., M.T.D., T.E., C.G., H.J.-C., D.H.K., A.F., J.G., A.I., J.F.K., M.M., K.M., N.N., T.E.O., P.A.R., G.S., D.C.S., R.R.Y., R.Z., B.J.F. and A.H. all provided photometric or radial velocity data that were important for the interpretation of the system. J.C. and E.J.G. provided the observations and analysis of the Keck AO data. E.L.N.J., D.J.J., D.B., I.A.C., D.L.D., G.A.E., A.G., M.D.J., R.B.K., J.L.-B., M.B.L., J.M., K.K.M., R.W.P., H.R., D.C.S., C.S., T.G.T., M.T. and P.T. have all been essential for the initiation and successful operation of the KELT-North and KELT-South surveys. All of the authors have read the manuscript and concur with the conclusions therein. The authors declare no competing financial interests.Attached Files
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Additional details
- Eprint ID
- 78092
- DOI
- 10.1038/nature22392
- Resolver ID
- CaltechAUTHORS:20170612-091354266
- AST-1056524
- NSF
- AST-1358862
- NSF
- NASA/JPL/Caltech
- 2014184874
- NSF Graduate Research Fellowship
- Harvard Future Faculty Leaders Postdoctoral Fellowship
- Fund for Astronomical Research
- JP25247026
- Japan Society for the Promotion of Science (JSPS)
- W. M. Keck Foundation
- Created
-
2017-06-12Created from EPrint's datestamp field
- Updated
-
2021-11-15Created from EPrint's last_modified field
- Caltech groups
- Infrared Processing and Analysis Center (IPAC)