TOI 540 b: A Planet Smaller than Earth Orbiting a Nearby Rapidly Rotating Low-mass Star

We present the discovery of TOI 540 b, a hot planet slightly smaller than Earth orbiting the low-mass star 2MASS J05051443-4756154. The planet has an orbital period of \(P = 1.239149\) days (\(\pm\) 170 ms) and a radius of \(r = 0.903 \pm 0.052 R_{\rm Earth}\), and is likely terrestrial based on the...

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Bibliographic Details
Published in:arXiv.org 2020-09
Main Authors: Kristo Ment, Irwin, Jonathan, Charbonneau, David, Winters, Jennifer G, Medina, Amber, Cloutier, Ryan, Díaz, Matías R, Jenkins, James S, Ziegler, Carl, Law, Nicholas, Mann, Andrew W, Ricker, George, Vanderspek, Roland, Latham, David W, Seager, Sara, Winn, Joshua N, Jenkins, Jon M, Goeke, Robert F, Levine, Alan M, Rojas-Ayala, Bárbara, Rowden, Pamela, Ting, Eric B, Twicken, Joseph D
Format: Article
Language:English
Subjects:
Bolometers
Earth
Earth rotation
Emission analysis
Extrasolar planets
Ground-based observation
Low mass stars
Luminosity
Orbits
Photometry
Planetary rotation
Spectrum analysis
Stellar rotation
XMM (spacecraft)
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Summary:We present the discovery of TOI 540 b, a hot planet slightly smaller than Earth orbiting the low-mass star 2MASS J05051443-4756154. The planet has an orbital period of \(P = 1.239149\) days (\(\pm\) 170 ms) and a radius of \(r = 0.903 \pm 0.052 R_{\rm Earth}\), and is likely terrestrial based on the observed mass-radius distribution of small exoplanets at similar insolations. The star is 14.008 pc away and we estimate its mass and radius to be \(M = 0.159 \pm 0.014 M_{\rm Sun}\) and \(R = 0.1895 \pm 0.0079 R_{\rm Sun}\), respectively. The star is distinctive in its very short rotational period of \(P_{\rm rot} = 17.4264 +/- 0.0094\) hours and correspondingly small Rossby number of 0.007 as well as its high X-ray-to-bolometric luminosity ratio of \(L_X / L_{\rm bol} = 0.0028\) based on a serendipitous XMM-Newton detection during a slew operation. This is consistent with the X-ray emission being observed at a maximum value of \(L_X / L_{\rm bol} \simeq 10^{-3}\) as predicted for the most rapidly rotating M dwarfs. TOI 540 b may be an alluring target to study atmospheric erosion due to the strong stellar X-ray emission. It is also among the most accessible targets for transmission and emission spectroscopy and eclipse photometry with JWST, and may permit Doppler tomography with high-resolution spectroscopy during transit. This discovery is based on precise photometric data from TESS and ground-based follow-up observations by the MEarth team.
ISSN:2331-8422