A giant planet undergoing extreme-ultraviolet irradiation by its hot massive-star host

Gaudi, B. Scott and Stassun, Keivan G. and Collins, Karen A. and Beatty, Thomas G. and Zhou, George ORCID: https://orcid.org/0000-0002-4891-3517 and Latham, David W. and Bieryla, Allyson and Eastman, Jason D. and Siverd, Robert J. and Crepp, Justin R. and Gonzales, Erica J. and Stevens, Daniel J. and Buchhave, Lars A. and Pepper, Joshua and Johnson, Marshall C. and Colon, Knicole D. and Jensen, Eric L. N. and Rodriguez, Joseph E. and Bozza, Valerio and Calchi Novati, Sebastiano and D'Ago, Giuseppe and Dumont, Mary T. and Ellis, Tyler and Gaillard, Clement and Jang-Condell, Hannah and Kasper, David H. and Fukui, Akihiko and Gregorio, Joao and Ito, Ayaka and Kielkopf, John F. and Manner, Mark and Matt, Kyle and Narita, Norio and Oberst, Thomas E. and Reed, Phillip A. and Scarpetta, Gaetano and Stephens, Denice C. and Yeigh, Rex R. and Zambelli, Roberto and Fulton, B. J. and Howard, Andrew W. and James, David J. and Penny, Matthew and Bayliss, Daniel and Curtis, Ivan A. and DePoy, D. L. and Esquerdo, Gilbert A. and Gould, Andrew and Joner, Michael D. and Kuhn, Rudolf B. and Labadie-Bartz, Jonathan and Lund, Michael B. and Marshall, Jennifer L. and McLeod, Kim K. and Pogge, Richard W. and Relles, Howard and Stockdale, Christopher and Tan, T. G. and Trueblood, Mark and Trueblood, Patricia (2017) A giant planet undergoing extreme-ultraviolet irradiation by its hot massive-star host. Nature, 546 (7659). ISSN 0028-0836

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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.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Faculty/School / Institute/Centre: No Faculty
Faculty/School / Institute/Centre: No Faculty
Date Deposited: 07 Feb 2022 05:21
Last Modified: 04 Apr 2022 08:02
Uncontrolled Keywords: ablation; high temperature; insolation; molecular analysis; planetary atmosphere; ultraviolet radiation; Astrophysics - Earth and Planetary Astrophysics
Fields of Research (2008): 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020110 Stellar Astronomy and Planetary Systems
Fields of Research (2020): 51 PHYSICAL SCIENCES > 5101 Astronomical sciences > 510109 Stellar astronomy and planetary systems
Socio-Economic Objectives (2008): E Expanding Knowledge > 97 Expanding Knowledge > 970102 Expanding Knowledge in the Physical Sciences
Socio-Economic Objectives (2020): 28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280120 Expanding knowledge in the physical sciences
Identification Number or DOI: https://doi.org/10.1038/nature22392
URI: http://eprints.usq.edu.au/id/eprint/44988

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