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Masses and compositions of three small planets orbiting the nearby M dwarf L231-32 (TOI-270) and the M dwarf radius valley

Van Eylen, V. ; Astudillo-Defru, N. ; Bonfils, X. ; Livingston, J. ; Hirano, T. ; Luque, R. ; Lam, K. W.F. ; Justesen, A. B. ; Winn, J. N. and Gandolfi, D. , et al. (2021) In Monthly Notices of the Royal Astronomical Society 507(2). p.2154-2173
Abstract

We report on precise Doppler measurements of L231-32 (TOI-270), a nearby M dwarf (d = 22 pc, M = 0.39 M, R = 0.38 R), which hosts three transiting planets that were recently discovered using data from the Transiting Exoplanet Survey Satellite (TESS). The three planets are 1.2, 2.4, and 2.1 times the size of Earth and have orbital periods of 3.4, 5.7, and 11.4 d. We obtained 29 high-resolution optical spectra with the newly commissioned Echelle Spectrograph for Rocky Exoplanet and Stable Spectroscopic Observations (ESPRESSO) and 58 spectra using the High Accuracy Radial velocity Planet Searcher (HARPS). From these observations, we find the masses of the planets to be 1.58 ± 0.26, 6.15 ± 0.37, and 4.78 ± 0.43 M, respectively. The... (More)

We report on precise Doppler measurements of L231-32 (TOI-270), a nearby M dwarf (d = 22 pc, M = 0.39 M, R = 0.38 R), which hosts three transiting planets that were recently discovered using data from the Transiting Exoplanet Survey Satellite (TESS). The three planets are 1.2, 2.4, and 2.1 times the size of Earth and have orbital periods of 3.4, 5.7, and 11.4 d. We obtained 29 high-resolution optical spectra with the newly commissioned Echelle Spectrograph for Rocky Exoplanet and Stable Spectroscopic Observations (ESPRESSO) and 58 spectra using the High Accuracy Radial velocity Planet Searcher (HARPS). From these observations, we find the masses of the planets to be 1.58 ± 0.26, 6.15 ± 0.37, and 4.78 ± 0.43 M, respectively. The combination of radius and mass measurements suggests that the innermost planet has a rocky composition similar to that of Earth, while the outer two planets have lower densities. Thus, the inner planet and the outer planets are on opposite sides of the 'radius valley'-a region in the radius-period diagram with relatively few members-which has been interpreted as a consequence of atmospheric photoevaporation. We place these findings into the context of other small close-in planets orbiting M dwarf stars, and use support vector machines to determine the location and slope of the M dwarf (Teff < 4000 K) radius valley as a function of orbital period. We compare the location of the M dwarf radius valley to the radius valley observed for FGK stars, and find that its location is a good match to photoevaporation and core-powered mass-loss models. Finally, we show that planets below the M dwarf radius valley have compositions consistent with stripped rocky cores, whereas most planets above have a lower density consistent with the presence of a H-He atmosphere.

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publishing date
type
Contribution to journal
publication status
published
keywords
planets and satellites: composition, planets and satellites: formation, planets and satellites: fundamental parameters, planets and satellites: individual: L231-32
in
Monthly Notices of the Royal Astronomical Society
volume
507
issue
2
pages
20 pages
publisher
Oxford University Press
external identifiers
  • scopus:85115835746
ISSN
0035-8711
DOI
10.1093/mnras/stab2143
language
English
LU publication?
no
additional info
Publisher Copyright: © 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.
id
5bffcee5-0d63-4aa5-8c9e-bd6a1d8ee4a4
date added to LUP
2023-02-01 10:09:47
date last changed
2023-02-21 11:22:04
@article{5bffcee5-0d63-4aa5-8c9e-bd6a1d8ee4a4,
  abstract     = {{<p>We report on precise Doppler measurements of L231-32 (TOI-270), a nearby M dwarf (d = 22 pc, M = 0.39 M, R = 0.38 R), which hosts three transiting planets that were recently discovered using data from the Transiting Exoplanet Survey Satellite (TESS). The three planets are 1.2, 2.4, and 2.1 times the size of Earth and have orbital periods of 3.4, 5.7, and 11.4 d. We obtained 29 high-resolution optical spectra with the newly commissioned Echelle Spectrograph for Rocky Exoplanet and Stable Spectroscopic Observations (ESPRESSO) and 58 spectra using the High Accuracy Radial velocity Planet Searcher (HARPS). From these observations, we find the masses of the planets to be 1.58 ± 0.26, 6.15 ± 0.37, and 4.78 ± 0.43 M, respectively. The combination of radius and mass measurements suggests that the innermost planet has a rocky composition similar to that of Earth, while the outer two planets have lower densities. Thus, the inner planet and the outer planets are on opposite sides of the 'radius valley'-a region in the radius-period diagram with relatively few members-which has been interpreted as a consequence of atmospheric photoevaporation. We place these findings into the context of other small close-in planets orbiting M dwarf stars, and use support vector machines to determine the location and slope of the M dwarf (Teff &lt; 4000 K) radius valley as a function of orbital period. We compare the location of the M dwarf radius valley to the radius valley observed for FGK stars, and find that its location is a good match to photoevaporation and core-powered mass-loss models. Finally, we show that planets below the M dwarf radius valley have compositions consistent with stripped rocky cores, whereas most planets above have a lower density consistent with the presence of a H-He atmosphere.</p>}},
  author       = {{Van Eylen, V. and Astudillo-Defru, N. and Bonfils, X. and Livingston, J. and Hirano, T. and Luque, R. and Lam, K. W.F. and Justesen, A. B. and Winn, J. N. and Gandolfi, D. and Nowak, G. and Palle, E. and Albrecht, S. and Dai, F. and Campos Estrada, B. and Owen, J. E. and Foreman-Mackey, D. and Fridlund, M. and Korth, J. and Mathur, S. and Forveille, T. and Mikal-Evans, T. and Osborne, H. L.M. and Ho, C. S.K. and Almenara, J. M. and Artigau, E. and Barragán, O. and Barros, S. C.C. and Bouchy, F. and Cabrera, J. and Caldwell, D. A. and Charbonneau, D. and Chaturvedi, P. and Cochran, W. D. and Csizmadia, S. and Damasso, M. and Delfosse, X. and De Medeiros, J. R. and Díaz, R. F. and Doyon, R. and Esposito, M. and Furész, G. and Figueira, P. and Georgieva, I. and Goffo, E. and Grziwa, S. and Guenther, E. and Hatzes, A. P. and Jenkins, J. M. and Kabath, P. and Knudstrup, E. and Latham, D. W. and Lavie, B. and Lovis, C. and Mennickent, R. E. and Mullally, S. E. and Murgas, F. and Narita, N. and Pepe, F. A. and Persson, C. M. and Redfield, S. and Ricker, G. R. and Santos, N. C. and Seager, S. and Serrano, L. M. and Smith, A. M.S. and Mascareño, A. Suárez and Subjak, J. and Twicken, J. D. and Udry, S. and Vanderspek, R. and Zapatero Osorio, M. R.}},
  issn         = {{0035-8711}},
  keywords     = {{planets and satellites: composition; planets and satellites: formation; planets and satellites: fundamental parameters; planets and satellites: individual: L231-32}},
  language     = {{eng}},
  month        = {{10}},
  number       = {{2}},
  pages        = {{2154--2173}},
  publisher    = {{Oxford University Press}},
  series       = {{Monthly Notices of the Royal Astronomical Society}},
  title        = {{Masses and compositions of three small planets orbiting the nearby M dwarf L231-32 (TOI-270) and the M dwarf radius valley}},
  url          = {{http://dx.doi.org/10.1093/mnras/stab2143}},
  doi          = {{10.1093/mnras/stab2143}},
  volume       = {{507}},
  year         = {{2021}},
}