Migration and Growth of Protoplanetary Embryos. III. Mass and Metallicity Dependence for FGKM Main-sequence Stars
Abstract
Radial velocity and transit surveys have found that the fraction of FGKM stars with close-in super-Earth(s) (η ⊕) is around 30%-50%, independent of the stellar mass M * and metallicity Z *. In contrast, the fraction of solar-type stars harboring one or more gas giants (η J) with masses M p > 100 M ⊕ is nearly 10%-15%, and it appears to increase with both M * and Z *. Regardless of the properties of their host stars, the total mass of some multiple super-Earths systems exceeds the core mass of Jupiter and Saturn. We suggest that both super-Earths and supercritical cores of gas giants were assembled from a population of embryos that underwent convergent type I migration from their birthplaces to a transition location between viscously heated and irradiation-heated disk regions. We attribute the cause for the η ⊕-η J dichotomy to conditions required for embryos to merge and to acquire supercritical core mass ({M}{{c}}∼ 10 {M}\oplus ) for the onset of efficient gaseous envelope accretion. We translate this condition into a critical disk accretion rate, and our analysis and simulation results show that it weakly depends on M * and decreases with metallicity of disk gas Z d. We find that embryos are more likely to merge into supercritical cores around relatively massive and metal-rich stars. This dependence accounts for the observed η J-M *. We also consider the {Z}{{d}}{--}{Z}* dispersed relationship and reproduce the observed η J-Z * correlation.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 2016
- DOI:
- 10.3847/0004-637X/823/2/162
- arXiv:
- arXiv:1605.05294
- Bibcode:
- 2016ApJ...823..162L
- Keywords:
-
- methods: numerical;
- planetary systems;
- planet–disk interactions;
- Astrophysics - Earth and Planetary Astrophysics
- E-Print:
- 20 pages, 10 figure, accepted in ApJ