Sunday, February 19, 2023

An Earth-sized Planet around an M5 Dwarf Star at 22 pc

 arXiv (accepted for publication in AJ):

We report on the discovery of an Earth-sized transiting planet (Rp=1.015±0.051R⊕) in a P=4.02 day orbit around K2-415 (EPIC 211414619), an M5V star at 22 pc.

Combining the light curves with the data secured by our follow-up observations including high-resolution imaging and near infrared spectroscopy with IRD, we rule out false positive scenarios, finding a low false positive probability of 2×10−4. Based on IRD’s radial velocities of K2-415, which were sparsely taken over three years, we obtain the planet mass of 3.0 ± 2.7 M⊕ (Mp < 7.5 M⊕ at 95 % confidence) for K2-415b. Being one of the lowest mass stars (≈ 0.16 M ) known to host an Earth-sized transiting planet, K2-415 will be an interesting target for further follow-up observations, including additional radial velocity monitoring and transit spectroscopy.

Figure 1. Light curves of K2-415 obtained by K2 (top; K2SFF) and TESS (bottom; PDC-SAP). Those data were taken at long (≈ 29 minutes) and short (2 minutes) cadences for K2 and TESS light curves, respectively. The red solid line in each panel represents the GP regression to the observed light curve (see Section 4.4).

"The K2-415 system is unique in that K2-415 is one of the coolest, or lowest-mass, stars known to host an exoplanet," Teruyuki Hirano of the Graduate University for Advanced Studies (SOKENDAI) in Japan, lead author on a paper about the discovery, told

"One motivation for investigating the planets around such low-mass stars is to understand and clarify whether those planets form and evolve just like the planets around solar-type stars," said Hirano. 

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