A comprehensive study of the relations between the properties of planetary systems and the chemical compositions of their host stars

TL;DR

This study analyzes 13 chemical elements in 561 Kepler planet-hosting stars using high-resolution Keck/HIRES spectra to explore how stellar composition relates to planetary system properties. It confirms that stars hosting large planets tend to be more metal-rich, with α-element enhancement potentially enabling giant-planet formation in metal-poor environments, though iron remains a limiting factor. Across planetary architectures, the authors find no robust, planet-specific [X/Fe]–Tc trends, and the Sun’s refractory depletion appears not to be caused by planet formation, a conclusion supported by solar-twin analyses. The work emphasizes that abundance signatures are largely governed by underlying iron content and Galactic chemical evolution, highlighting the need for high-S/N spectra to refine such correlations.

Abstract

The giant planet-metallicity correlation revealed that planetary formation depends on the stellar properties. There is growing evidence that it is also valid for smaller hot planets, but it is not clear whether elements other than iron also influence the properties of planetary systems. To investigate this, we determined the abundances of 13 chemical elements (Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni and Cu) for a sample of 561 Kepler exoplanet-hosting stars using high-resolution Keck/HIRES spectra. We find that stars in systems having only large or hot planets are enriched in some elements relative to those having only small or warm planets, respectively, with this signature being related to the underlying stellar metallicity. This Kepler sample is composed of stars belonging to the Galactic low- and high-$α$ sequences, corresponding to the chemical thin and thick disks. Our results reveal that stars enhanced in $α$-elements may facilitate the formation of large planets in metal-poor environments although the iron abundance is still a limiting factor. We also investigated chemical abundances as a function of elemental condensation temperatures and found that there is a diversity of slopes regardless of the exoplanetary systems hosted by the star. We confirmed that the Sun is depleted in refractory elements relative to the solar twins in our sample, all of which host a diversity of exoplanets, suggesting that this depletion is caused by processes not related to planet formation.

Figures (13)

• Figure 1: Kiel diagram for our sample of 561 stars. The stellar metallicities are represented by the color bar.
• Figure 2: Distributions of 16 chemical abundances (13 elements, including three - Sc, Ti and Cr - with two ionization stages) for the 561 stars in our work (blue) and 1368 stars from luck17luck18 (red). Note that they provide a single set of abundances for Sc, Ti, and Cr, and we use them in the comparisons with both ionization stages we analyzed for these elements. The solid vertical blue and red lines represent the median values (M), which are also shown in each panel along with the corresponding MAD, from our work and luck17luck18, respectively. The median M($\sigma$) and MAD values for the total uncertainties in our abundances are also shown in each panel.
• Figure 3: Left panel: The abundances of 16 species (13 elements, including three - Sc, Ti and Cr - with two ionization stages) determined for the HIRES spectrum of the sunlight reflected off Vesta from ghezzi18. Right panel: Absolute differences between the abundances determined for the 16 species in the solar spectrum with varying S/N values (300, 250, 200, 150, 100, 90, 80, 70, 60, 50, 40, 30, 20, and 10) and the values from asplund09. Points in blue and red represent spectra with S/N $\geq$ 30 and S/N $<$ 30, respectively. Note there are six points with differences larger than 0.15 dex (five for S/N = 10 and one for S/N = 20) not shown in the figure for better visualization purposes.
• Figure 4: Comparison between the abundances from this work and rescaled abundances (see text) from brewer18 (B18). For each species, the upper panels show the direct comparison between the values, and the lower panels present the differences $\Delta$[X/H] (This work - B18). Note that brewer18 provide a single set of abundances for Ti and Cr, and we use them in the comparisons with both ionization stages we analyzed for these elements. The solid black lines show a perfect agreement, while dotted and dashed black lines represent, respectively, differences of 0.1 and 0.2 dex as a reference. The red-dashed lines show the linear fits, for which the slopes are shown in each panel, along with the median differences.
• Figure 5: Chemical abundances [X/Fe] of 16 species (13 elements, including three - Sc, Ti and Cr - with two ionization stages) as a function of [Fe/H] for the 510 stars in our work. The dashed black lines show the solar values for reference.