Stellar characterization, Magnesium Abundances and Chromospheric Activity Analysis of Stars with Confirmed Exoplanets from the K2 mission

TL;DR

This study provides a detailed spectroscopic analysis of 301 confirmed exoplanet host stars from the K2 mission, revealing correlations between stellar properties, chemical abundances, and exoplanet characteristics, including the radius gap and activity levels.

Contribution

It offers a homogeneous dataset of stellar parameters and chemical abundances for K2 exoplanet hosts, linking stellar composition and activity to exoplanet sizes and populations.

Findings

Detection of the radius gap near 1.9 R⊕ with precise measurements.

Stellar activity decreases with increasing planetary radius within low-activity stars.

Stars hosting larger planets are more metal-rich in iron and magnesium.

Abstract

We present a homogeneous spectroscopic analysis of confirmed K2 mission exoplanet-hosting stars, comprising 301 targets with high-resolution optical spectra from HIRES and TRES taken from ExoFOP. We derived effective temperatures, surface gravities, and iron and magnesium abundances in LTE by measuring the equivalent widths of Fe I, Fe II, and Mg I lines. Three estimates of stellar masses and radii were obtained via Stefan-Boltzmann and isochrone methods using the codes PARAM and isochrones. These were used to derive exoplanetary radii reaching internal precisions of 2.5%, 2.6%, and 6.6%, respectively, and the radius gap being consistently detected near 1.9 R$_{\oplus}$. We measured chromospheric activity from the Ca II H & K and H$\alpha$ lines. Within the low-activity range ($\log R^{\prime}_{HK} < -4.75$), stellar activity appears to decrease with increasing planetary radius from super-Earths, sub-Neptunes, sub-Saturns, into the Jupiter regime. According to the [Mg/Fe] measurements, most of our K2 planet hosts belong to the Galactic thin disk, but our sample has a population from the thick disk (high-alpha sequence). Most stars show consistent chemo-dynamical behavior. We find that the [Mg/Fe] ratios are indistinguishable between systems containing Large or Small exoplanets, as well as Single- or Multi-exoplanetary systems. Both the [Fe/H] and [Mg/H] distributions reveal that stars hosting large planets are more iron- and magnesium-enhanced than those having only small planets, further confirming the link between stellar abundances and exoplanetary size, but no significant differences are found between the Single- versus Multi-exoplanetary systems.