Automatic detection of chromospheric plages in the Coimbra Observatory spectroheliograms

Full-disk spectroheliograms have been routinely taken in Coimbra since 1926 in the Ca II K3 line and in the K1v line from 1973 onwards. Additionally, in 1990 started regular observations in the Hα line. More, in 2007 the photographic plates were replaced by a CCD camera. This extensive collection acquired with the same instrumentation must be processed all together since its large temporal coverage can provide important inputs for the knowledge of the solar activity. In this study we applied the mathematical morfology approach to the CA II K3 series to detect automatically and analyse the chromospheric plages. To evaluate the performance of the method, the results were compared with the observations obtained by a human operator and solar catalogs, showing very good results. Evolution of the solar activity in the solar cycle 24 have been in focus. To validate the capabilities of the software tool we compared the results of detection for the solar cycle 23 obtained using the presented method with those obtained using a software tools developed in the OGAUC already in 2004.