Issue |
Astron. Astrophys. Suppl. Ser.
Volume 130, Number 3, June II 1998
|
|
---|---|---|
Page(s) | 513 - 526 | |
DOI | https://doi.org/10.1051/aas:1998237 | |
Published online | 15 June 1998 |
Calcium triplet synthesis *
1
Villafranca del Castillo Satellite Tracking Station, P.O. Box 50727, 28080 Madrid, Spain
2
Osservatorio Astronomico di Padova, Vicolo dell' Osservatorio 5, I-35122 Padova, Italy
3
Dipartamento di Fisica, Università di Pisa, Piazza Torricelli 2, I-56100 Pisa, Italy
Received:
20
March
1997
Accepted:
26
January
1998
We present theoretical equivalent widths for the sum of the two strongest
lines of the calcium triplet, CaT index, in the near-IR (
8542, 8662 Å), using evolutionary synthesis techniques and the most
recent models and observational data for this feature in individual stars.
We compute the CaT index for Single Stellar Populations (instantaneous
burst, standard Salpeter-type IMF) at four different metallicities,
, 0.008, 0.02 (solar) and 0.05, and ranging in age from very young
bursts of star formation (few Myr) to old stellar populations, up to 17
Gyr, representative of galactic globular clusters, elliptical galaxies and
bulges of spirals. The interpretation of the observed equivalent widths of CaT
in different stellar systems is discussed.
Composite-population models are also computed as a tool to interpret the
CaT detections in star-forming regions, in order to disentangle between
the component due to Red Supergiant stars, RSG,
and the underlying, older, population. CaT is found to
be an excellent metallicity-indicator for populations older than
1 Gyr, practically independent of the age. We discuss its application to
remove the age-metallicity degeneracy, characteristic of all studies of
galaxy evolution based on the usual integrated indices (both broad band
colors and narrow band indices). The application of the models computed
here to the analysis of a sample of elliptical galaxies will be
discussed in a forthcoming paper (Gorgas et al. 1997).
Key words: galaxies: stellar content; starbursts; elliptical
© European Southern Observatory (ESO), 1998