Rotation periods of late-type dwarf stars from time series high-resolution spectroscopy of chromospheric indicators

Abstract

We determine rotation periods of a sample of 48 late F-type to mid-M dwarf\nstars using time-series high-resolution spectroscopy of the Ca II H&K and\nH-alpha chromospheric activity indicators. We find good agreement between the\nrotation periods obtained from each of these two indicators. An empirical\nrelationship between the level of chromospheric emission measured by log (R'HK)\nand the spectroscopic rotation periods is reported. This relation is largely\nindependent of the spectral type and the metallicity of the stars and can be\nused to make a reliable prediction of rotation periods for late K to mid-M\ndwarfs with low levels of activity. For some stars in the sample, the measured\nspectroscopic rotation periods coincide, or are very close, to the orbital\nperiods of postulated planets. In such cases, further studies are needed to\nclarify whether the associated periodic radial velocity signals reveal the\nexistence of planets or are due to magnetic activity.\n