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Journal Articles Monthly Notices of the Royal Astronomical Society Year : 2022

One year of AU Mic with HARPS - I. Measuring the masses of the two transiting planets

Norbert Zicher
  • Function : Author
Oscar Barragán
  • Function : Author
Baptiste Klein
  • Function : Author
Suzanne Aigrain
  • Function : Author
James E. Owen
  • Function : Author
Davide Gandolfi
  • Function : Author
Luisa Maria Serrano
  • Function : Author
Laurel Kaye
  • Function : Author
Louise Dyregaard Nielsen
  • Function : Author
Vinesh Maguire Rajpaul
  • Function : Author
Elisa Goffo
  • Function : Author
Belinda Nicholson
  • Function : Author


The system of two transiting Neptune-sized planets around the bright, young M-dwarf AU Mic provides a unique opportunity to test models of planet formation, early evolution, and star-planet interaction. However, the intense magnetic activity of the host star makes measuring the masses of the planets via the radial velocity (RV) method very challenging. We report on a 1-yr, intensive monitoring campaign of the system using 91 observations with the HARPS spectrograph, allowing for detailed modelling of the ~600 ${\rm m\, s^{-1}}$ peak-to-peak activity-induced RV variations. We used a multidimensional Gaussian Process framework to model these and the planetary signals simultaneously. We detect the latter with semi-amplitudes of Kb = 5.8 ± 2.5 ${\rm m\, s^{-1}}$ and Kc = 8.5 ± 2.5 ${\rm m\, s^{-1}}$, respectively. The resulting mass estimates, Mb = 11.7 ± 5.0 M and Mc = 22.2 ± 6.7 M, suggest that planet b might be less dense, and planet c considerably denser than previously thought. These results are in tension with the current standard models of core-accretion. They suggest that both planets accreted a H/He envelope that is smaller than expected, and the trend between the two planets' envelope fractions is the opposite of what is predicted by theory.
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insu-03705346 , version 1 (27-06-2022)


Attribution - CC BY 4.0



Norbert Zicher, Oscar Barragán, Baptiste Klein, Suzanne Aigrain, James E. Owen, et al.. One year of AU Mic with HARPS - I. Measuring the masses of the two transiting planets. Monthly Notices of the Royal Astronomical Society, 2022, 512, pp.3060-3078. ⟨10.1093/mnras/stac614⟩. ⟨insu-03705346⟩
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