A Mini-Neptune Orbiting the Metal-poor K Dwarf BD+29 2654

Fei Dai, Kevin C. Schlaufman, Henrique Reggiani, Luke Bouma, Andrew W. Howard, Ashley Chontos, Daria Pidhorodetska, Judah Van Zandt, Joseph M. Akana Murphy, Ryan A. Rubenzahl, Alex S. Polanski, Jack Lubin, Corey Beard, Steven Giacalone, Rae Holcomb, Natalie M. Batalha, Ian Crossfield, Courtney Dressing, Benjamin Fulton, Daniel HuberHoward Isaacson, Stephen R. Kane, Erik A. Petigura, Paul Robertson, Lauren M. Weiss, Alexander A. Belinski, Andrew W. Boyle, Christopher J. Burke, Amadeo Castro-González, David R. Ciardi, Tansu Daylan, Akihiko Fukui, Holden Gill, Natalia M. Guerrero, Coel Hellier, Steve B. Howell, Jorge Lillo-Box, Felipe Murgas, Norio Narita, Enric Pallé, David R. Rodriguez, Arjun B. Savel, Avi Shporer, Keivan G. Stassun, Stephanie Striegel, Douglas A. Caldwell, Jon M. Jenkins, George R. Ricker, Sara Seager, Roland Vanderspek, Joshua N. Winn

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


We report the discovery and Doppler mass measurement of a 7.4 days 2.3 R mini-Neptune around a metal-poor K dwarf BD+29 2654 (TOI-2018). Based on a high-resolution Keck/HIRES spectrum, the Gaia parallax, and multiwavelength photometry from the UV to the mid-infrared, we found that the host star has T eff = 4174 − 42 + 34 K, log g = 4.62 − 0.03 + 0.02 , [Fe/H] = − 0.58 ± 0.18, M * = 0.57 ± 0.02 M , and R * = 0.62 ± 0.01 R . Precise Doppler measurements with Keck/HIRES revealed a planetary mass of M p = 9.2 ± 2.1 M for TOI-2018 b. TOI-2018 b has a mass and radius that are consistent with an Earthlike core, with a ∼1%-by-mass hydrogen/helium envelope or an ice-rock mixture. The mass of TOI-2018 b is close to the threshold for runaway accretion and hence giant planet formation. Such a threshold is predicted to be around 10M or lower for a low-metallicity (low-opacity) environment. If TOI-2018 b is a planetary core that failed to undergo runaway accretion, it may underline the reason why giant planets are rare around low-metallicity host stars (one possibility is their shorter disk lifetimes). With a K-band magnitude of 7.1, TOI-2018 b may be a suitable target for transmission spectroscopy with the James Webb Space Telescope. The system is also amenable to metastable Helium observation; the detection of a Helium exosphere would help distinguish between a H/He-enveloped planet and a water world.

Original languageEnglish (US)
Article number49
JournalAstronomical Journal
Issue number2
StatePublished - Aug 1 2023

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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