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Correlations between Planet Occurrence and Detailed Stellar Chemistry

Presentation #102.09 in the session Poster Session.

Published onJun 20, 2022
Correlations between Planet Occurrence and Detailed Stellar Chemistry

Because the composition of the planet-forming environment is encoded in the composition of a planet’s host star, chemical abundances may offer a unique glimpse into the formation, evolution, and even the geological and atmospheric properties of exoplanets. Such differences have been inferred from the increase in planet occurrence with increasing stellar metallicity, but it is unclear if such trends integrate over more detailed chemical relationships. To further explore this connection, we made the first ever occurrence rate measurement for planets in the Kepler field as a function of chemical abundance for ten different elements (C, Mg, Al, Si, S, K, Ca, Mn, Fe, and Ni).

From a sample of >1000 stars with Kepler planet candidates observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE), we leverage multi epoch observations to remove RV variable sources and apply the combined high resolution, high S/N spectra to derive stellar properties to precisely and uniformly infer planetary radii. Within this sample, the enhancement of any element in our study correlates to an increase in plant occurrence. As seen in previous studies that used Fe abundances only, the strength of the correlation is dependent on orbital period and planet type, with shorter period planets and larger radius planets having the strongest correlations. This holds true across all elements, but we are not able to unambiguously attribute the correlation between planet occurrence and stellar chemistry to the enhancement of any one element or combination of elements.

These results point to a larger challenge which has been noted in samples of RV-detected planets. The enhancement or depletion of individual elements are highly correlated due to Galactic Chemical Evolution so disentangling the influence of specific elements requires planet searches over distinct stellar populations. However, performing such a search will invariably lead to constructing biased samples of planet-search stars with differing age and mass distributions. To help control for such differences, we advocate for large-scale spectroscopic surveys to provide uniformly derived metallicities and chemical abundances not only for planet-hosting stars but also for a significant fraction of field stars, to accurately and homogeneously infer stellar ages and masses.

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