<p>From my understanding D4000 is a ratio between the 'flux densities between 4050 and 4250 Angstroms and that between 3750 and 3950 Angstrom', from <a href="https://arxiv.org/abs/astro-ph/9703067" rel="nofollow noreferrer">Poggianti et al (1997)</a>. 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.</p>

CC BY-SA 4.0
2018-08-09T17:22:16.870Z
Are there strong Lithium lines in this wavelength range?
AtmosphericPrisonEscape
CC BY-SA 4.0
2018-08-09T19:09:55.620Z
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 https://physics.nist.gov/PhysRefData/Handbook/Tables/lithiumtable2.htm 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
<astrophysics><spectroscopy><stellar-evolution>
Why does D4000 affect stellar age?
QuantumPanda
# Why does D4000 affect stellar age?

(Asked by: username_0 on 2018-08-09)

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)](https://arxiv.org/abs/astro-ph/9703067). 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.

**Tags:** astrophysics, spectroscopy, stellar-evolution

> **Comments:**
> **username_1**: Are there strong Lithium lines in this wavelength range?  
> **username_2**: 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 https://physics.nist.gov/PhysRefData/Handbook/Tables/lithiumtable2.htm 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.  

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## 0 answers

