II. Test and calibration with high resolution observations
Istituto Nazionale di Astrofisica – Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy e-mail: firstname.lastname@example.org
2 Max-Planck-Institut für Sonnensystemforschung, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany e-mail: email@example.com
3 Istituto Nazionale di Astrofisica – Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy e-mail: [andretta;gomez;terranegra]@na.astro.it
Accepted: 24 January 2007
Aims.We report on our analysis of the high resolution spectra () of a sample of 42 late-type active stars (with measured spanning from to ) acquired with the Italian 3.6 m Telescopio Nazionale Galileo (TNG) using the SARG spectrometer in the 4960-10 110 Å range. The high quality of the spectra and the good activity-level coverage allow us to measure two different chromospheric indicators that can be derived from the Ca ii infrared triplet (Ca ii IRT) lines: the residual equivalent width (EQW) and the chromospheric indicator . The aim of this work is determine and test the best way of deriving activity-level information and errors from the Ca ii IRT lines, in preparation of the GAIA Cornerstone mission by ESA, by which the Ca ii IRT spectral range will be spectroscopically observed for millions of stars.
Methods.The index is calculated for each observed star as the difference between the calculated NLTE photospheric central intensity and the observed one. The residual EQW, , is calculated as the area of the positive profile obtained as the difference between the calculated NLTE photospheric and the observed profiles. We correlate with and the .
Results.This analysis indicates that Ca ii IRT lines are good chromospheric diagnostics. We find that both and the quantities can be used as chromospheric indicators, although the former exhibits a tighter correlation with the index. Furthermore, we find that the total chromospheric excess EQW in the Ca ii IRT is almost linearly correlated with the excess in the Ca ii H & K doublet, as estimated through the index.
Key words: stars: atmospheres / radiative transfer / line: formation / stars: chromospheres / stars: activity
Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Centro Galileo Galilei of the Consorzio Nazionale per l'Astronomia e l'Astrofisica at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.
© ESO, 2007