Chromospheric activity and late stellar evolution

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Using our robotic TIGRE telescope located in Guanajuato, Mexico, we have begun a long-term monitoring program of giants to systematically study the atmospheric and chromospheric properties of these stars; we have specifically been observing a sample of 30 late-type giants over the last four years using high-resolution spectroscopy. A large fraction of the sample stars had already earlier been monitored in the context of the Mount Wilson H&K project over more than a decade and in some cases even longer, and these monitoring data have recently become publicly available. For various reasons (discussed in detail in our application) the Mt. Wilson H&K data on giants have never been properly analyzed and published.An examination of these archival data shows that --somewhat surprisingly-- the chromospheric activity of giants high up on the red and asymptotic giant branches appears to be increasing, in line with recent measurements of magnetic fields in such objects. What is missing, however, is a quantitative measure of the chromospheric energy losses of such objects as well as an in-depth study of their temporal variability characteristics.In the context of this project application we therefore propose to do exactly this. We specifically propose to study and characterize quantitatively the activity increase of red giants on their red and asymptotic giant branches, to develop quantitative methods to measure chromospheric fluxes from giant stars in the Ca~II H&K lines and the Ca~II infrared triplet lines measured in high-resolution spectra. From these we propose to develop the tools to quantitatively interpret the S-index data for giants and hence to study and characterize chromospheric variability of giants on time scales of years to decade. Finally, we propose to use the data to compare the spectral and temporal variability patterns of giants and main sequence stars.