12 Years of Stellar Activity Observations in Argentina

MAUAS, P. J. D.; BUCCINO, A.P.; DÍAZ, R. F.; VIEYTES, M. C.; PETRUCCI, R.; JOFRE, E.; ABREVAYA, X. C.; LUONI, M.L.; VALENZUELA, P.

Mendoza

Congreso; IAU Symposium 286: Comparative Magnetic Minima: Characterizing quiet times in the Sun and stars; 2011

IAU

We present an observational program we started in 1999, to systematically obtainmid-resolution spectra of late-type stars, to study in particular chromospheric activity. In par-ticular, we found cyclic activity in four dM stars, including Prox-Cen. We directly derived theconversion factor that translates the known S index to flux in the Ca II cores, and extend itscalibration to a wider spectral range. We investigated the relation between the activity mea-surements in the calcium and hydrogen lines, and found that the usual correlation observed isthe product of the dependence of each flux on stellar color, and it is not always preserved whensimultaneous observations of a particular star are considered. We also used our observationsto model the chromospheres of stars of different spectral types and activity levels, and foundthat the integrated chromospheric radiative losses, normalized to the surface luminosity, showa unique trend for G and K dwarfs when plotted against the S index.