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-year, intensive monitoring campaign of the system using 91 observations with the HARPS spectrograph, allowing for detailed modelling of the similar to 600 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 K-b = 5.8 +/- 2.5 m s(-1) and K-c = 8.5 +/- 2.5 m s(-1), respectively. The resulting mass estimates, M-b = 11.7 +/- 5.0 M-circle plus and M-c = 22.2 +/- 6.7 M-circle plus, 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.

One year of AU Mic with HARPS: I - measuring the masses of the two transiting planets

Davide Gandolfi;Luisa Maria Serrano;Elisa Goffo;
2022-01-01

Abstract

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-year, intensive monitoring campaign of the system using 91 observations with the HARPS spectrograph, allowing for detailed modelling of the similar to 600 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 K-b = 5.8 +/- 2.5 m s(-1) and K-c = 8.5 +/- 2.5 m s(-1), respectively. The resulting mass estimates, M-b = 11.7 +/- 5.0 M-circle plus and M-c = 22.2 +/- 6.7 M-circle plus, 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.
2022
512
2
3060
3078
https://academic.oup.com/mnras/article/512/2/3060/6547782
techniques: radial velocities; techniques: spectroscopic; stars: individual: AU Microscopii; planets and satellites: fundamental parameters; stars: activity; stars: starspots
Norbert Zicher; Oscar Barrag??n; Baptiste Klein; Suzanne Aigrain; James E Owen; Davide Gandolfi; Anne-Marie Lagrange; Luisa Maria Serrano; Laurel Kaye...espandi
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2318/1948550
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