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Abstract
ABSTRACT We report the discovery of TOI-530b, a transiting Saturn-like planet around an M0.5V dwarf, delivered by the Transiting Exoplanet Survey Satellite (TESS). The host star is located at a distance of 147.7 ± 0.6 pc with a radius of R* = 0.54 ± 0.03 R⊙ and a mass of M* = 0.53 ± 0.02 M⊙. We verify the planetary nature of the transit signals by combining ground-based multiwavelength photometry, high-resolution spectroscopy from SPIRou as well as high-angular-resolution imaging. With V = 15.4 mag, TOI-530b is orbiting one of the faintest stars accessible by ground-based spectroscopy. Our model reveals that TOI-530b has a radius of 0.83 ± 0.05 RJ and a mass of 0.37 ± 0.08 MJ on a 6.39-d orbit. TOI-530b is the sixth transiting giant planet hosted by an M-type star, which is predicted to be infrequent according to core accretion theory, making it a valuable object to further study the formation and migration history of similar planets. Furthermore, we identify a potential dearth of hot massive giant planets around M-dwarfs with separation distance smaller than 0.1 au and planet-to-star mass ratio between 2 × 10−3 and 10−2. We also find a possible correlation between hot giant planet formation and the metallicity of its parent M-dwarf. We discuss the potential formation channel of such systems.
Highlights
M-dwarfs are popular targets for exoplanet research
Dynamic nested sampling is applied in juliet to determine the posterior estimates of system parameters using the publicly available package dynesty (Higson et al 2019; Speagle 2020)
As the Transiting Exoplanet Survey Satellite (TESS) Presearch Data Conditioning Simple Aperture Photometry (PDCSAP) light curve has already been corrected for the light dilution, we fix the dilution factors D to 1
Summary
M-dwarfs are popular targets for exoplanet research. First, radial velocity (RV) variations induced by the planets around M-dwarfs are more significant than those around solar-like stars, making it possible to obtain precise mass measurement towards the terrestrial planet end of the mass distribution. Even though M-dwarfs are the most abundant stellar population in our Milky Way (Henry et al 2006), only five giant planets have been confirmed to transit them: Kepler-45b (Johnson et al 2012), HATS6b (Hartman et al 2015), NGTS-1b (Bayliss et al 2018), HATS71b (Bakos et al 2020), and TOI-1899b (Canas et al 2020) The deficiency of such systems is thought to be caused by the failed growth of a massive core to start runaway accretion before the gaseous protoplanetary disc dissipates due to the low surface density (Laughlin, Bodenheimer & Adams 2004; Ida & Lin 2005; Kennedy & Kenyon 2008; Liu & Ji 2020). Further Rossiter–McLaughlin (McLaughlin 1924; Rossiter 1924) or Doppler tomography (Marsh 2001) measurements could reveal the obliquity of these systems, providing important clues about the dynamical history of the planets (e.g. Albrecht et al 2012)
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