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Chromospheric activity monitoring of a wide range of cool stars can providevaluable information on stellar magnetic activity and its dependence onfundamental stellar parameters such as effective temperature and rotation.Wecompile a chromospheric activity catalogue of 4454 cool stars from acombination of archival HARPS spectra and multiple other surveys, including theMount Wilson data that have recently been released by the NSO. We explore thevariation in chromospheric activity of cool stars along the main sequence forstars with different effective temperatures. Additionally, we also perform anactivity-cycle period search and investigate its relation with rotation. Thechromospheric activity index, S-index, was measured for 304 main-sequence starsfrom archived high-resolution HARPS spectra. Additionally, the measured andarchived S-indices were converted into the chromospheric flux ratio log R'HK.The activity-cycle periods were determined using the generalised Lomb-Scargleperiodogram to study the active and inactive branches on therotation-activity-cycle period plane. The global sample shows that thebimodality of chromospheric activity, known as the Vaughan-Preston gap, is notprominent, with a significant percentage of the stars at anintermediate-activity level around log R'HK = -4.75. Independently, the cycleperiod search shows that stars can lie in the region intermediate between theactive and inactive branch, which means that the active branch is not asclearly distinct as previously thought. The weakening of the Vaughan-Prestongap indicates that cool stars spin down from a higher activity level and settleat a lower activity level without a sudden break at intermediate activity. Somecycle periods are close to the solar value between the active and inactivebranch, which suggests that the solar dynamo is most likely a common case ofthe stellar dynamo.

Chromospheric activity catalogue of 4454 cool stars. Questioning the active branch of stellar activity cycles