An alpha element is an element such as oxygen, neon or magnesium associated with nucleosynthesis involving helium nuclei and massive-star burning. Core-collapse supernovae promptly return substantial abundances of these elements. Their abundance relative to iron can distinguish a rapid enrichment history from one with substantial delayed Type Ia supernova enrichment.
Massive stars produce prompt enrichment through core-collapse supernovae, whereas a Type Ia supernova follows binary stellar evolution and contributes substantial iron after a distribution of delays. A stellar population formed rapidly before much delayed enrichment can have a larger alpha-element to iron ratio than a stellar population formed over a prolonged interval. Relative abundance also depends on the initial mass function, stellar yields, and gas exchange; this is a chemical clock with model assumptions.
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