Zodiacal exoplanets in time – XI. The orbit and radiation environment of the young M dwarf-hosted planet K2-25b. (14th August 2020)

• Record Type: Journal Article
• Authors: Gaidos, E; Hirano, T; Wilson, D J; France, K; Rockcliffe, K; Newton, E; Feiden, G; Krishnamurthy, V; Harakawa, H; Hodapp, K W; Ishizuka, M; Jacobson, S; Konishi, M; Kotani, T; Kudo, T; Kurokawa, T; Kuzuhara, M; Nishikawa, J; Omiya, M; Serizawa, T; Tamura, M; Ueda, A; Vievard, S
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 498:Number 1(2020)
• Page Start: L119
• Page End: L124
• Publication Date: 2020-08-14
• Subjects: techniques: spectroscopic -- Sun: UV radiation -- planets and satellites: atmospheres -- planets and satellites: physical evolution -- stars: activity -- planetary systems; Astronomy -- Research -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnrasl/slaa136
• Languages: English
• ISSNs: 1745-3933

Abstract

ABSTRACT: M dwarf stars are high-priority targets for searches for Earth-size and potentially Earth-like planets, but their planetary systems may form and evolve in very different circumstellar environments than those of solar-type stars. To explore the evolution of these systems, we obtained transit spectroscopy and photometry of the Neptune-size planet orbiting the ≈650-Myr-old Hyades M dwarf K2-25. An analysis of the variation in spectral line shape induced by the Doppler 'shadow' of the planet indicates that the planet's orbit is closely aligned with the stellar equator ($\lambda =-1.7_{-3.7}^{+5.8}$ deg), and that an eccentric orbit found by previous work could arise from perturbations by another planet on a coplanar orbit. We detect no significant variation in the depth of the He i line at 1083 nm during transit. A model of atmospheric escape as an isothermal Parker wind with a solar composition shows that this non-detection is not constraining compared to escape rate predictions of ∼0.1 M⊕ Gyr −1 ; at such rates, at least several Gyr are required for a Neptune-like planet to evolve into a rocky super-Earth.