Beliebiger Eintrag,
Planet Traps and Planetary Cores: Origins of the Planet-Metallicity Correlation
(08.08.2014)
Zusammenfassung
Massive exoplanets are observed preferentially around high metallicity
(Fe/H) stars while low-mass exoplanets do not show such an effect. This
so-called planet-metallicity correlation generally favors the idea that most
observed gas giants at \$r<10\$ AU are formed via a core accretion process. We
investigate the origin of this phenomenon using a semi-analystical model,
wherein the standard core accretion takes place at planet traps in protostellar
disks where rapid type I migrators are halted. We focus on the three major
exoplanetary populations - hot-Jupiters, exo-Jupiters located at \$r 1\$
AU, and the low-mass planets. We show using a statistical approach that the
planet-metallicity correlations are well reproduced in these models. We find
that there are specific transition metallicities with values Fe/H\$=-0.2\$ to
\$-0.4\$, below which the low-mass population dominates, and above which the
Jovian populations take over. The exo-Jupiters significantly exceed the
hot-Jupiter population at all observed metallicities. The low-mass planets
formed via the core accretion are insensitive to metallicity, which may account
for a large fraction of the observed super-Earths and hot-Neptunes. Finally, a
controlling factor in building massive planets is the critical mass of
planetary cores (\$M\_c,crit\$) that regulates the onset of runaway gas
accretion. Assuming the current data is roughly complete at Fe/H\$>-0.6\$, our
models predict that the most likely value of the "mean" critical core mass of
Jovian planets is \$M\_c,crit 5 M\_øplus\$ rather than \$10
M\_øplus\$. This implies that grain opacities in accreting envelopes should
play an important role in lowering \$M\_c,crit\$.
