Absence of extended atmospheres in low-mass star radius-gap planets. Issue 1 (6th February 2023)

• Record Type: Journal Article
• Authors: Krishnamurthy, Vigneshwaran; Hirano, Teruyuki; Gaidos, Eric; Sato, Bunei; Kopparapu, Ravi; Barclay, Thomas; Garcia-Sage, Katherine; Harakawa, Hiroki; Hodapp, Klaus; Jacobson, Shane; Konishi, Mihoko; Kotani, Takayuki; Kudo, Tomoyuki; Kurokawa, Takashi; Kuzuhara, Masayuki; Lopez, Eric; Nishikawa, Jun; Omiya, Masashi; Schlieder, Joshua E; Serizawa, Takuma; Tamura, Motohide; Ueda, Akitoshi; Vievard, Sebastien
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 521:Issue 1(2023)
• Page Start: 1210
• Page End: 1220
• Publication Date: 2023-02-06
• Subjects: techniques: spectroscopic -- planets and satellites: atmospheres -- stars: activity -- stars: late-type -- stars: low-mass -- planetary systems; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stad404
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: Kepler showed a paucity of planets with radii of 1.5–2 R⊕ around solar mass stars but this radius-gap has not been well studied for low-mass star planets. Energy-driven escape models like photoevaporation and core-powered mass-loss predict opposing transition regimes between rocky and non-rocky planets when compared to models depicting planets forming in gas-poor environments. Here, we present transit observations of three super-Earth sized planets in the radius-gap around low-mass stars using high-dispersion InfraRed Doppler spectrograph on the Subaru 8.2 m telescope. The planets GJ 9827 b and d orbit around a K6V star and TOI-1235 b orbits a M0.5 star. We limit any planet-related absorption in the 1083.3 nm lines of triplet He i by placing an upper-limit on the equivalent width of 14.71, 18.39, and 1.44 mÅ for GJ 9827 b (99 per cent confidence), GJ 9827 d (99 per cent confidence), and TOI-1235 b (95 per cent confidence), respectively. Using a Parker wind model, we cap the mass-loss at >0.25 M⊕ Gyr −1 and >0.2 M⊕ Gyr −1 for GJ 9827 b and d, respectively (99 per cent confidence), and >0.05 M⊕ Gyr −1 for TOI-1235 b (95 per cent confidence) for a representative wind temperature of 5000 K. Our observed results for the three planets are more consistent with the predictions from photoevaporation and/or core-powered mass-loss models than the gas-poor formation models. However, more planets in the radius-gap regime around the low-mass stars are needed to robustly predict the atmospheric evolution in planets around low-mass stars.