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The main chromospheric activity indicator is the S index, which is esentiallythe ratio of the flux in the core of the Ca II H and K lines to the continuumnearby, and is well studied basically for stars from F to K. Another usualchromospheric proxy is the H\alpha line, which is beleived to be tightlycorrelated with the Ca II index. In this work we characterize bothchromospheric activity indicators, one associated with the H and K Ca II linesand the other with H\alpha, for the whole range of late type stars, from F toM. We present periodical medium-resolution echelle observations covering thecomplete visual range, which were taken at the CASLEO Argentinean Observatory.These observations are distributed along 7 years. We use a total of 917flux-calibrated spectra for 109 stars which range from F6 to M5. Westatistically study these two indicators for stars of different activity levelsand spectral types. We directly derive the conversion factor which translatethe known S index to flux in the Ca II cores, and extend its calibration to awider spectral range. We investigate the relation between the activitymeasurements in the calcium and hydrogen lines, and found that the usualcorrelation observed is basically the product of the dependence of each fluxwith stellar colour, and not the product of similar activity phenomena.Comment: 12 pages, including 11 figures and 2 tables. Accepted for publication  in Astronomy and Astrophysic

Hαand the Ca II H and K lines as activity proxies for late-type stars