  Radial-velocity (RV) jitter caused by stellar magnetic activity is an
important factor in state-of-the-art exoplanet discovery surveys such as
CARMENES. Stellar rotation, along with heterogeneities in the photosphere and
chromosphere caused by activity, can result in false-positive planet
detections. Hence, it is necessary to determine the stellar rotation period and
compare it to any putative planetary RV signature. Long-term measurements of
activity indicators such as the chromospheric emission in the Ca II H&K lines
enable the identification of magnetic activity cycles. In order to determine
stellar rotation periods and study the long-term behavior of magnetic activity
of the CARMENES guaranteed time observations (GTO) sample, it is advantageous
to extract Ca II H&K time series from archival data, since the CARMENES
spectrograph does not cover the blue range of the stellar spectrum containing
the Ca II H&K lines. We have assembled a catalog of 11634 archival spectra of
186 M dwarfs acquired by seven different instruments covering the Ca II H&K
regime: ESPADONS, FEROS, HARPS, HIRES, NARVAL, TIGRE, and UVES. The relative
chromospheric flux in these lines was directly extracted from the spectra by
rectification with PHOENIX synthetic spectra via narrow passbands around the Ca
ii H&K line cores. The combination of archival spectra from various instruments
results in time series for 186 stars from the CARMENES GTO sample. As an
example of the use of the catalog, we report the tentative discovery of three
previously unknown activity cycles of M dwarfs. We conclude that the method of
extracting Ca II H&K fluxes with the use of model spectra yields consistent
results for different instruments and that the compilation of this catalog will
enable the analysis of long-term activity time series for a large number of M
dwarfs.
