Two planets for the young star HD 63433. The study: “The GAPS Programme at TNG XLII. A characterisation study of the multi-planet system around the 400 Myr-old star HD 63433 (TOI-1726)” of M. Damasso (INAF – OATo) appeared on A&A
The search and characterization of exoplanets around young stars (where “young” here means less than 600 million years) is crucial for advancing our understanding of planetary formation processes and the early stages of planet evolution. During this phase, the planetary environment is significantly more turbulent compared to that of mature exoplanetary systems. For example, many planets in young systems continue to undergo dynamic evolution, leading to increased collision rates. Additionally, young stars exhibit higher X-ray and UV emissions compared to older stars. The absorption of this radiation by planetary atmospheres can result in significant mass loss. Furthermore, in the case of the youngest planets, they are still embedded within their protoplanetary disks, which continue to interact with them, facilitating accretion and inducing rapid radial migration.
Given these circumstances, numerous projects are dedicated to the search and characterization of young exoplanets. One such project is GAPS (Global Architecture of Planetary Systems), which has allocated a substantial portion of observing time using the HARPS-N spectrograph, installed on the Telescopio Nazionale Galileo, to study planets younger than 600 million years.
This is the framework of the recent study led by the astronomer M. Damasso (INAF – Osservatorio Astrofisico di Torino), which presents the characterization of two planets orbiting the star HD 63433. This star belongs to the Ursa Major moving group and is only 400 million years old. The discovery of these two planets was made in 2016 through observations conducted by the NASA satellite TESS. Subsequently, they were observed with HARPS-N as part of the GAPS program from February 2020 to April 2022, collecting a total of 103 spectroscopic observations. By analyzing these observations along with new TESS data and observations from the STELLA telescope, the research team calculated precise orbital periods for the planets (7.1 and 20.5 days) and determined upper limits for their masses (≤11 and ≤31 Earth masses). Furthermore, using appropriate models and considering the decline in X-ray emission from the parent star, the authors estimated that HD 63433 b has already lost its primordial atmosphere, which was rich in hydrogen and helium. On the other hand, the atmosphere of HD 63433 c, if the planetary mass is smaller than 15 Earth masses, is currently undergoing evaporation and will continue to do so for approximately 4.5 billion years. The study is described in the paper titled “The GAPS Programme at TNG XLII. A characterisation study of the multi-planet system around the 400 Myr-old star HD 63433 (TOI-1726)“, recently published in the journal Astronomy & Astrophysics. This study has been coordinated with a research led by astronomers of the Instituto de Astrofisica de Canarias based on observations of the CARMENES spectrograph mounted on the Calar Alto Observatory. Among the coauthors are the astronomers D. Locci, S. Benatti, A. Maggio, J. Maldonano, and G. Micela from INAF – Osservatorio Astronomico di Palermo.
The figure (click here to view the complete image) illustrates the predicted evolution of HD 63433 c. Panel a displays the mass loss rate versus time for different predictions of planetary mass. Panel b shows the planetary mass loss over time. Panels c and d depict the time evolution of the planetary mass and radius, respectively.
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