Two Bright M Dwarfs Hosting Ultra-Short-Period Super-Earths with Earth-like Compositions
Teruyuki Hirano, John H. Livingston, Akihiko Fukui, Norio Narita,, Hiroki Harakawa, Hiroyuki Tako Ishikawa, Kohei Miyakawa, Tadahiro Kimura,, Akifumi Nakayama, Naho Fujita, Yasunori Hori, Keivan G. Stassun, Allyson, Bieryla, Charles Cadieux, David R. Ciardi, Karen A. Collins

TL;DR
This study reports the discovery and characterization of two ultra-short-period super-Earths orbiting bright M dwarfs, confirming their Earth-like compositions and providing insights into their formation and properties.
Contribution
First detailed mass and radius measurements of two bright M dwarf USP planets, establishing their Earth-like compositions and highlighting TOI-1634b as the most massive USP planet.
Findings
Both planets have Earth-like densities.
TOI-1634b is the most massive USP planet known.
TOI-1685 shows potential additional planets or noise.
Abstract
We present observations of two bright M dwarfs (TOI-1634 and TOI-1685: ) hosting ultra-short period (USP) planets, identified by the TESS mission. The two stars are similar in temperature, mass, and radius ( K, , and ), and the planets are both super-Earth-sized (). For both systems, light curves from the ground-based photometry exhibit planetary transits, whose depths are consistent with those by the TESS photometry. We also refine the transit ephemerides based on the ground-based photometry, finding the orbital periods of day and day for TOI-1634b and TOI-1685b, respectively. Through intensive radial velocity (RV) observations using IRD on the Subaru 8.2m telescope, we confirm the…
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