intermediate population star

An intermediate population star is a star with properties between those of extreme Population I stars in the galactic spiral arms and extreme Population II stars in the galactic halo. Intermediate population I stars move in circular orbits but are distributed throughout the galactic disk not just in the arms. They are somewhat older than the extreme population I stars with ages in the range 200 million to 10 billion years. Their metallicites range from 1 to 2% of their overall chemical composition. Our Sun belongs to this class, as do most of the visually observable stars in the disk. Intermediate population II stars are typically at least several billion years old with a metallicity of around 0.8%. They are found in the inner parts of the halo and the galactic bulge (though the bulge also contains population I stars with high metallic ties). Intermediate population II stars outside of the halo are not confined to circular orbits or to the disk, instead moving in moderately elliptical orbits though still centered on the galactic nucleus.