| Issue |
A&A
Volume 466, Number 3, May II 2007
|
|
|---|---|---|
| Page(s) | 1089 - 1098 | |
| Section | Stellar atmospheres | |
| DOI | https://doi.org/10.1051/0004-6361:20065588 | |
| Published online | 24 April 2007 | |
The Ca II infrared triplet as a stellar activity diagnostic *,**
II. Test and calibration with high resolution observations
1
Istituto Nazionale di Astrofisica – Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy e-mail: ebu@oact.inaf.it
2
Max-Planck-Institut für Sonnensystemforschung, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany e-mail: aznar@mps.mpg.de
3
Istituto Nazionale di Astrofisica – Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy e-mail: [andretta;gomez;terranegra]@na.astro.it
Received:
11
May
2006
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
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