Chemical composition of planetary hosts

The determination of stellar parameters is based on a standard analysis using equivalent widths and one-dimensional, plane-parallel model atmospheres calculated under the assumption of local thermodynamical equilibrium. The differential synthetic spectrum method was used to uniformly determine the carbon C(C2), nitrogen N(CN), oxygen [OI], magnesium MgI, and silicon SiI elemental abundances as well as the C/O, N/O and Mg/Si ratios.

We analysed elemental abundances and ratios in dwarf and giant stars, finding that [C/Fe], [O/Fe], and [Mg/Fe] are lower in metal-rich dwarf hosts while [N/Fe] is close to the Solar ratio. Giants show smaller scatter in [C/Fe] and [O/Fe] and lower than the Solar average [C/Fe] and C/O ratios. The (C+N+O) abundances increase with [Fe/H] in giant stars, with a minimal scatter.

We also noted an overabundance of Mg and Si in planet-hosting stars, particularly at lower metallicities, and a lower Mg/Si ratio in stars with planets. In giants hosting high-mass planets, nitrogen shows a moderate positive relationship with planet mass. C/O and N/O ratios show moderate negative and positive slopes in giant stars, respectively.

Mg/Si ratio shows a negative correlation with planet mass across the entire stellar sample.