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 extra-solar planets now known, only four giant planets have been found that transit hot, A-type stars (temperatures of 7300-10,000K), and none are known to transit even hotter B-type stars. WASP-33 is an A-type star with a temperature of ~7430K, which hosts the hottest known transiting planet; the planet is itself as hot as a red dwarf star of type M. The planet displays a large heat differential between its day-side and night-side, and is highly inflated, traits that have been linked to high insolation. However, even at the temperature of WASP-33b's day-side, its atmosphere likely resembles the molecule-dominated atmospheres of other planets, and at the level of ultraviolet irradiation it experiences, its atmosphere is unlikely to be significantly ablated over the lifetime of its star. Here we report observations of the bright star HD 195689, which reveal a close-in (orbital period ~1.48 days) transiting giant planet, KELT-9b. At ~10,170K, the host star is at the dividing line between stars of type A and B, and we measure the KELT-9b's day-side temperature to be ~4600K. This is as hot as stars of stellar type K4. The molecules in K stars are entirely dissociated, and thus the primary sources of opacity in the day-side atmosphere of KELT-9b are likely atomic metals. Furthermore, KELT-9b receives ~700 times more extreme ultraviolet radiation (wavelengths shorter than 91.2 nanometers) 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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Cite
@article{arxiv.1706.06723,
title = {A giant planet undergoing extreme ultraviolet irradiation by its hot massive-star host},
author = {B. Scott Gaudi and Keivan G. Stassun and Karen A. Collins and Thomas G. Beatty and George Zhou and David W. Latham and Allyson Bieryla and Jason D. Eastman and Robert J. Siverd and Justin R. Crepp and Erica J. Gonzales and Daniel J. Stevens and Lars A. Buchhave and Joshua Pepper and Marshall C. Johnson and Knicole D. Colon and Eric L. N. Jensen and Joseph E. Rodriguez and Valerio Bozza and Sebastiano Calchi Novati and Giuseppe D'Ago and Mary T. Dumont and Tyler Ellis and Clement Gaillard and Hannah Jang-Condell and David H. Kasper and Akihiko Fukui and Joao Gregorio and Ayaka Ito and John F. Kielkopf and Mark Manner and Kyle Matt and Norio Narita and Thomas E. Oberst and Phillip A. Reed and Gaetano Scarpetta and Denice C. Stephens and Rex R. Yeigh and Roberto Zambelli and B. J. Fulton and Andrew W. Howard and David J. James and Matthew Penny and Daniel Bayliss and Ivan A. Curtis and D. L. DePoy and Gilbert A. Esquerdo and Andrew Gould and Michael D. Joner and Rudolf B. Kuhn and Jonathan Labadie-Bartz and Michael B. Lund and Jennifer L. Marshall and Kim K. McLeod and Richard W. Pogge and Howard Relles and Chistopher Stockdale and T. G. Tan and Mark Trueblood and Patricia Trueblood},
journal= {arXiv preprint arXiv:1706.06723},
year = {2017}
}
Comments
39 pages, 3 figures, 1 table, 3 extended data figures, 3 extended data tables. Published in Nature on 22 June 2017