Indicators of star formation: 4000 Angstrom break and Balmer lines

The behaviour of the 4000 Angstrom break index and of the equivalent width of the main Balmer lines is investigated a) for a single star as a function of effective temperature, gravity and metallicity and b) for a single stellar population as a function of age and metallicity. Consequences for the interpretation of integrated spectra are presented.
5 pages, needs A&A l-aa.sty, accepted for publication in Astronomy & Astrophysics, complete preprint with figures available on request at bianca@ast.cam.ac.uk