From my understanding D4000 is a ratio between the 'flux densities between 4050 and 4250 Angstroms and that between 3750 and 3950 Angstrom', from Poggianti et al (1997). However I do not understand why this is a direct relationship with stellar age. Did someone just notice that D4000 has a strong correlation to stellar age, if so what is the scientific explanation of this relationship.

  • Are there strong Lithium lines in this wavelength range? – AtmosphericPrisonEscape Aug 9 at 17:22
  • The Lithium abundance and age (up to very approx 600 Myr) is measured from the Li I 6708 angstrom line as it it by far the strongest. According to there are basically no lines at all in the wavelength range of the question. Suspect the lines in this region are gravity-sensitive and so will give crude measure of age. Main sequence stars have log g ~4.5, decreasing as they age and evolve off the main sequence and go up the giant branch. – astrosnapper Aug 9 at 19:09

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