Metallicity of Host Stars for Exoplanets

 

Exoplanet Populations and their Dependence on Host Star Properties

Gijs D. Mulders
" Figure 1:Trends in the exoplanet population as function of stellar mass and metallicity, illustrating the different behavior of the giant planet population (large pink circles) and planets smaller than Neptune (small cyan circles). The location of the sun is indicated with a yellow star. The location of individual symbols is randomly generated, with the density of point corresponding to the exoplanet occurrence rate. Any resemblance between symbol locations and observed exoplanets is entirely coincidental. "

https://arxiv.org/html/1805.00023v2

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Massive stars are more likely to host fewer planets in general as compared to lower mass stars.

High metallicity stars stars are more likely to host giant planets, low metallicity high mass stars tend to host some giant planets. Low mass low metallicity stars typically don't host giant planets. 

hypothesis:  the metallicity of a host star is likely to be similar to the metallicity of the star the hosted planet evolved from. Low mass low metallicity stars are more likely to turn into smaller planets. High mass high metallicity stars are more likely to turn into larger planets.

This is, if it is the case that proto stars will evolve into main sequence stars of different masses and metallicities according to their environment. So for example, a proto star may evolve to become a yellow dwarf, or larger white star, or blue giant depending on how much mass it gains from the nebula it forms in and depending on metallicity. In some areas such as globular clusters and dwarf elliptical galaxies, main sequence stars are more likely to be less massive and lower metallicity.

( In the standard model, on the other hand, this correlation is attributed to core accretion effect. "It has been established that the increased occurrence of giant planets around high-metallicity stars arises because giant planet cores are more likely to form in disks with a larger amount of solids" ... 

("These trends, however, breaks down for planets smaller than Neptune, hereafter sub-Neptunes, which poses some urgent questions about the planet formation process. Why is the frequency of sub-Neptunes almost independent of stellar metallicity, even when the initial inventory of condensible solids must have varied by an order of magnitude? " )