An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

A discontinuity in the spectrum of galaxies near the Ca II → H and K lines at about 4000 Å. The Ca break is the most prominent feature in the spectra of elliptical galaxies. Its strength is given by the → calcium break index.

→ calcium; → break.

The strength of the → calcium break, as measured from the fluxes in the intervals 3750-3950 Å and 4050-4250 Å. It is given by the expression Ca-break[%] = 100 · (f_upper - f_lower)/f_upper, where f_upper and f_lower are the mean fluxes measured in the 3750-3950 Å and 4050-4250 Å bands, respectively, in the rest frame (Dressler & Shectman 1987, AJ 94, 899).

→ calcium; → break; → index.