We compare the metallicities of stars with radial velocity planets to the metallicity of a sample of field dwarfs .
We confirm recent work indicating that the stars-with-planet sample as a whole is iron rich .
However , the lowest mass stars tend to be iron poor , with several having { [ Fe / H ] } < -0.2 , demonstrating that high metallicity is not required for the formation of short period Jupiter-mass planets .
We show that the average [ Fe/H ] increases with increasing stellar mass ( for masses below 1.25 M _ { \odot } ) in both samples , but that the increase is much more rapid in the stars-with-planet sample .
The variation of metallicity with stellar age also differs between the two samples .
We examine possible selection effects related to variations in the sensitivity of radial velocity surveys with stellar mass and metallicity , and identify a color cutoff ( B - V { \gtrsim } 0.48 ) that contributes to but does not explain the mass-metallicity trend in the stars-with-planets sample .
We use Monte Carlo models to show that adding an average of 6.5 M _ { \oplus } of iron to each star can explain both the mass-metallicity and the age-metallicity relations of the stars-with-planets sample .
However , for at least one star , HD 38529 , there is good evidence that the bulk metallicity is high .
We conclude that the observed metallicities and metallicity trends are the result of the interaction of three effects ; accretion of \sim 6 M _ { \oplus } of iron rich material , selection effects , and in some cases , high intrinsic metallicity .