Zodiacal exoplanets in time - XI. The orbit and radiation environment of the young M dwarf-hosted planet K2-25b
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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- October 2020
- DOI:
- 10.1093/mnrasl/slaa136
- arXiv:
- arXiv:2007.12701
- Bibcode:
- 2020MNRAS.498L.119G
- Keywords:
-
- techniques: spectroscopic;
- Sun: UV radiation;
- planets and satellites: atmospheres;
- planets and satellites: physical evolution;
- stars: activity;
- planetary systems;
- Astrophysics - Earth and Planetary Astrophysics;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- to appear in MNRAS Letters