title: Interacting supernovae from photoionization-confined shells around red supergiant stars.
abstract: Betelgeuse, a nearby red supergiant, is a fast-moving star with a powerful stellar wind that drives a bow shock into its surroundings. This picture has been challenged by the discovery of a dense and almost static shell that is three times closer to the star than the bow shock and has been decelerated by some external force. The two physically distinct structures cannot both be formed by the hydrodynamic interaction of the wind with the interstellar medium. Here we report that a model in which Betelgeuse's wind is photoionized by radiation from external sources can explain the static shell without requiring a new understanding of the bow shock. Pressure from the photoionized wind generates a standing shock in the neutral part of the wind and forms an almost static, photoionization-confined shell. Other red supergiants should have much more massive shells than Betelgeuse, because the photoionization-confined shell traps up to 35 per cent of all mass lost during the red supergiant phase, confining this gas close to the star until it explodes. After the supernova explosion, massive shells dramatically affect the supernova light curve, providing a natural explanation for the many supernovae that have signatures of circumstellar interaction.
authors.affiliation: Argelander-Institut für Astronomie, Auf dem Hügel 71, 53121 Bonn, Germany.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Mackey
authors.affiliation: South African Astronomical Observatory, PO Box 9, 7935 Observatory, South Africa.
authors.forename: Shazrene
authors.initials: S
authors.lastname: Mohamed
authors.affiliation: 1] Sternberg Astronomical Institute, Lomonosov Moscow State University, Universitetskij Prospect 13, Moscow 119992, Russia [2] Isaac Newton Institute of Chile, Moscow Branch, Universitetskij Prospect 13, Moscow 119992, Russia [3] Space Research Institute, Russian Academy of Sciences, Profsoyuznaya 84/32, Moscow 117997, Russia.
authors.forename: Vasilii V
authors.initials: VV
authors.lastname: Gvaramadze
authors.affiliation: Astrophysics Research Centre, School of Mathematics and Physics, Queen's University Belfast, Belfast BT7 1NN, UK.
authors.forename: Rubina
authors.initials: R
authors.lastname: Kotak
authors.affiliation: Argelander-Institut für Astronomie, Auf dem Hügel 71, 53121 Bonn, Germany.
authors.forename: Norbert
authors.initials: N
authors.lastname: Langer
authors.affiliation: Argelander-Institut für Astronomie, Auf dem Hügel 71, 53121 Bonn, Germany.
authors.forename: Dominique M-A
authors.initials: DM
authors.lastname: Meyer
authors.affiliation: Argelander-Institut für Astronomie, Auf dem Hügel 71, 53121 Bonn, Germany.
authors.forename: Takashi J
authors.initials: TJ
authors.lastname: Moriya
authors.affiliation: Department of Physics and Astronomy, East Tennessee State University, Box 70652, Johnson City, Tennessee 37614, USA.
authors.forename: Hilding R
authors.initials: HR
authors.lastname: Neilson