Chromospherically Active Stars in the MeerKAT Galactic Plane Survey

Abstract Stellar magnetic activity has long been established to occur in subsets of late-type main-sequence stars and manifests itself in the form of chromospheric and coronal activity. This activity is driven by magnetic fields generated by dynamo mechanisms associated with stellar rotation and convection, which channel and dissipate magnetic energy to the outer atmospheric layers. Optical spectroscopic follow-up was carried out for 99 radio-X-ray coronally active stars of G-, K-, and M-spectral types in the SARAO MeerKAT Galactic plane survey point sources. There are 46 stars that exhibited chromospheric activity. Specifically, 39 stars show Ca ii H&K emission lines, whereas 18 show Ca ii IRT, 11 show both H&K and IRT lines. Of the 39 stars displaying H&K emission, 37 show activity levels greater than the Solar minimum activity. Their X-ray to bolometric luminosity ratios are within the coronal thresholds of >−4.5. In addition, we explored optical photometry to investigate the rotation information and found that these stars show short rotation periods; in comparison with activity levels, the activity levels dampen as the rotation periods increase. We also analysed optical light curves for a subset of stars, and they show flaring behaviour at the same epoch as enhanced chromospheric activity, indicating the flares and chromospheric emission are manifestations of the same underlying magnetic activity process.