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

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


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 Huber

Howard 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

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


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 Teff=4174−42+34 K, logg=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.

Journal Article Type Article
Acceptance Date Jun 13, 2023
Online Publication Date Jul 7, 2023
Publication Date Aug 1, 2023
Deposit Date Jul 10, 2023
Publicly Available Date Jul 10, 2023
Journal The Astronomical Journal
Print ISSN 0004-6256
Electronic ISSN 1538-3881
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 166
Issue 2
Article Number 49
Keywords Exoplanets, Ocean planets, Mini Neptunes


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