The origin of the high metallicity of close-in giant exoplanets: Combined effect of the resonant and aerodynamic shepherding. (arXiv:1911.02292v1 [astro-ph.EP])

The origin of the high metallicity of close-in giant exoplanets: Combined effect of the resonant and aerodynamic shepherding. (arXiv:1911.02292v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Shibata_S/0/1/0/all/0/1">Sho Shibata</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Helled_R/0/1/0/all/0/1">Ravit Helled</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ikoma_M/0/1/0/all/0/1">Masahiro Ikoma</a>

Context.Recent studies suggest that many giant exoplanets are highly enriched
with heavy elements compared to their host star andcontain several tens of
Earth masses or more of heavy elements. Such enrichment is considered to have
been brought by accretionof planetesimals in late formation stages. Previous
dynamical simulations, however, show that planets are unable to collect so
muchheavy elements throughin situplanetesimal accretion. Aims.We investigate
whether a giant planet migrating inward can capture planetesimals efficiently
to significantly increase its metal-licity. Methods.We performed orbital
integrations of a migrating giant planet and planetesimals in a protoplanetary
gas disc to infer theplanetesimal mass that is accreted by the planet.
Results.We find that the two shepherding processes of mean motion resonances
trapping and aerodynamic gas drag inhibit plan-etesimal capture of a migrating
planet. However, the amplified libration allows the highly-excited
planetesimals in the resonances toescape from the resonance trap and be
accreted by the planet. Consequently, we show that a migrating giant planet
captures planetes-imals with total mass of several tens of Earth masses, if the
planet forms at a few tens of AU in a relatively massive disc. We alsofind that
planetesimal capture occurs efficiently in a limited range of semi-major axis,
and that the total captured planetesimal massincreases with increasing
migration distances. Our results have important implications for understanding
the relation between giantplanet metallicity and mass, as we suggest that it
reflects the formation location of the planet, or more precisely, the location
whererunaway gas accretion occurred. We also suggest the observed metal-rich
close-in Jupiters migrated to their present locations fromafar, where they
formed.

Context.Recent studies suggest that many giant exoplanets are highly enriched
with heavy elements compared to their host star andcontain several tens of
Earth masses or more of heavy elements. Such enrichment is considered to have
been brought by accretionof planetesimals in late formation stages. Previous
dynamical simulations, however, show that planets are unable to collect so
muchheavy elements throughin situplanetesimal accretion. Aims.We investigate
whether a giant planet migrating inward can capture planetesimals efficiently
to significantly increase its metal-licity. Methods.We performed orbital
integrations of a migrating giant planet and planetesimals in a protoplanetary
gas disc to infer theplanetesimal mass that is accreted by the planet.
Results.We find that the two shepherding processes of mean motion resonances
trapping and aerodynamic gas drag inhibit plan-etesimal capture of a migrating
planet. However, the amplified libration allows the highly-excited
planetesimals in the resonances toescape from the resonance trap and be
accreted by the planet. Consequently, we show that a migrating giant planet
captures planetes-imals with total mass of several tens of Earth masses, if the
planet forms at a few tens of AU in a relatively massive disc. We alsofind that
planetesimal capture occurs efficiently in a limited range of semi-major axis,
and that the total captured planetesimal massincreases with increasing
migration distances. Our results have important implications for understanding
the relation between giantplanet metallicity and mass, as we suggest that it
reflects the formation location of the planet, or more precisely, the location
whererunaway gas accretion occurred. We also suggest the observed metal-rich
close-in Jupiters migrated to their present locations fromafar, where they
formed.

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