# X-ray Activity from Different Types of Stars

## TL;DR

This study analyzes stellar X-ray activity across different star types using large datasets, revealing bimodal distributions linked to stellar rotation and magnetic activity, and establishing correlations between coronal and chromospheric indicators.

## Contribution

It provides a significantly larger sample of X-ray emitting stars and uncovers bimodal activity distributions related to stellar rotation and magnetic dynamo processes.

## Key findings

- Bimodal distribution of X-ray to optical flux ratio in G and K stars.
- Stars in inactive peaks have smaller rotational velocities.
- Strong correlation between X-ray activity and Hα emission luminosity.

## Abstract

X-ray emission is an important indicator of stellar activity. In this paper, we study stellar X-ray activity using the XMM-Newton and LAMOST data for different types of stars. We provide a sample including 1259 X-ray emitting stars, of which 1090 have accurate stellar parameter estimations. Our sample size is much larger than those in previous works. We find a bimodal distribution of X-ray to optical flux ratio (log(fX/fV)) for G and K stars. We interpret that this bimodality is due to two subpopulations with different coronal heating rates. Furthermore, using the full widths at half maxima calculated from H{\alpha} and H\b{eta} lines, we show that these stars in the inactive peaks have smaller rotational velocities. This is consistent with the magnetic dynamo theory that stars with low rotational velocities have low levels of stellar activity. We also examine the correlation between log(fX/fV) and luminosity of the excess emission in the H{\alpha} line, and find a tight relation between the coronal and chromospheric activity indicators.