Astron. Astrophys. Suppl. Ser. 139, 29-41

Empirical calibration of the $\lambda$4000 Å break

J.Gorgas¹ - N.Cardiel¹ - S.Pedraz¹ - J.J.González²

Send offprint request: J. Gorgas

Correspondence to: fjg@astrax.fis.ucm.es

1 - Departamento de Astrofísica, Facultad de Ciencias Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
2 - Instituto de Astronomía, U.N.A.M., Apdo. Postal 70-264, 04510 Mexico D.F., Mexico

Received March 18, accepted May 11, 1999

Abstract:

Empirical fitting functions, describing the behaviour of the $\lambda$4000 Å break, D₄₀₀₀, in terms of effective temperature, metallicity and surface gravity, are presented. For this purpose, the break has been measured in 392 stars from the Lick/IDS Library. We have followed a very detailed error treatment in the reduction and fitting procedures, allowing for a reliable estimation of the break uncertainties. This calibration can be easily incorporated into stellar population models to provide accurate predictions of the break amplitude for, relatively old, composite systems.

Key words: stars: fundamental parameters -- galaxies: stellar content -- techniques: spectroscopic -- stars: atmospheres