Old-disk star

Old-disk star is a member of a population of stars in a spiral galaxy, such as the Milky Way. Astronomers divide the members of the galactic disk into two stellar populations: thick disk and thin disk. The thick disk is an older component with stars that have significantly lower levels of metals—a term used to describe the abundance of elements other than hydrogen and helium. The thick disk formed early in a galaxy's history, typically within a billion years. Members of the thick disk are referred to as old-disk stars.[1]

References

  1. ↑ Freeman, Kenneth C. (Nov 12, 2010), Block, David L.; Freeman, Kenneth; Puerari, Ivânio, eds., "The HERMES Project: Reconstructing Galaxy Formation", Galaxies and their Masks: A Conference in Honour of K.C. Freeman, FRS (Springer Science & Business Media): 319, doi:10.1007/978-1-4419-7317-7_27, ISBN 978-1-4419-7316-0