Ca+II+break

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The Ca II break or the Calcium Break is a phenomenon where a drop in the flux level around 4000Å (wavelength). The way to calculate the Break is given by this formula: Fb is the flux level on blue side (the right) of the Ca II absorption line (around 3750~3950Å). Fr is the flux level on red side (the left) of the Ca II absorption line (around 4050~4250Å). One thing to keep in mind: you have to take into account the redshift of the galaxy when doing a Ca II break calculation. You can do so by multiplying the measured wavelengths by 1+z, z being the redshift, so from (1+z)(3750Å) to (1+z)(3950Å) and (1+z)(4050Å) to (1+z)(4250Å).