Empirical Calibration of the Near-IR Ca II Triplet

Paper I

Empirical calibration of the near-IR Ca II triplet - I. The stellar library and index definition

Cenarro A.J., Cardiel N., Gorgas J., Peletier R.F., Vazdekis A. and Prada F.


A new stellar library at the near-IR spectral region developed for the empirical calibration of the Ca II triplet and stellar population synthesis modeling is presented. The library covers the range 8348 Å - 9020 Å at 1.5 Å (FWHM) spectral resolution, and consists of 706 stars spanning a wide range in atmospheric parameters. We have defined a new set of near-IR indices, CaT*, CaT and PaT, which mostly overcome the limitations of previous definitions, the former being specially suited for the measurement of the Ca II triplet strength corrected for the contamination from Paschen lines. We also present a comparative study of the new and the previous calcium indices, as well as the corresponding transformations between the different systems. A thorough analysis of the sources of index errors and the procedure to calculate them is given. Finally, index and error measurements for the whole stellar library are provided together with the final spectra.

New indices definitions

CaT and PaT indices over different spectral types. The spectra correspond (from top to bottom) to HD161817 (A2 VI), HD25329 (K1 Vsb) and HD148783 (M6 III). Grey and open bands represent continuum and central bandpasses respectively, with the solid line showing the derived local pseudo-continuum.

Bandpasses limits

CaT central bandpasses (Å)

PaT central bandpasses (Å)

Continuum bandpasses (Å)

Ca1: 8484.0 - 8513.0

Pa1: 8461.0 - 8474.0

8474.0 - 8484.0

Ca2: 8522.0 - 8562.0

Pa2: 8577.0 - 8619.0

8563.0 - 8577.0

Ca3: 8642.0 - 8682.0

Pa3: 8730.0 - 8772.0

8619.0 - 8642.0

8700.0 - 8725.0

8776.0 - 8792.0

Paper I is published in MNRAS, 326, 959 (2001)

Full information of the library stars is given in this Database

The Spectra of the whole stellar library are also available.

Free Software for measuring indices.