학술논문
A Mini-Neptune Orbiting the Metal-poor K Dwarf BD+29 2654
Document Type
Working Paper
Author
Dai, Fei; Schlaufman, Kevin C.; Reggiani, Henrique; Bouma, Luke; Howard, Andrew W.; Chontos, Ashley; Pidhorodetska, Daria; Van Zandt, Judah; Murphy, Joseph M. Akana; 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.
Source
Subject
Language
Abstract
We report the discovery and Doppler mass measurement of a 7.4-day 2.3-$R_\oplus$ 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 multi-wavelength photometry from the ultraviolet to the mid-infrared, we found that the host star has $T_{\text{eff}}=4174^{+34}_{-42}$ K, $\log{g}=4.62^{+0.02}_{-0.03}$, $[\text{Fe/H}]=-0.58\pm0.18$, $M_{\ast}=0.57\pm0.02~M_{\odot}$, and $R_{\ast}=0.62\pm0.01~R_{\odot}$. Precise Doppler measurements with Keck/HIRES revealed a planetary mass of $M_{\text{p}}=9.2\pm2.1~M_{\oplus}$ for TOI-2018 b. TOI-2018 b has a mass and radius that are consistent with an Earth-like core with a $\sim1\%$-by-mass hydrogen/helium envelope, or an ice-rock mixture. The mass of TOI-2018 b is close to the threshold for run-away accretion and hence giant planet formation. Such a threshold is predicted to be around 10$M_\oplus$ or lower for a low-metallicity (low-opacity) environment. If TOI-2018 b is a planetary core that failed to undergo run-away 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.
Comment: 10 figures, 5 tables, accepted to AAS Journals
Comment: 10 figures, 5 tables, accepted to AAS Journals