| Abstract : | Stars of all ages are found near the sun- young and old, with abundances up to about [Fe/H] = 0.5. The most metal-rich stars with [Fe/H] > 0.1, could not have formed near the sun, because the interstellar medium near the sun is not so metal-rich. It is widely believed that they formed in the inner Galaxy and migrated out to solar neighborhood via radial migration.
The migration process moves stars from near-circular orbits at one radius to near-circular orbits at another (mostly larger) radius via transient torques (e.g. from spiral structure), and their vertical dispersion is lower after the migration, due to the conservation of z-action. These processes may work together to produce an observed age-velocity relation for the solar neighborhood, similar to that for stars born near the sun.
We study the abundances and motions of stars with [Fe/H] > 0.1 near the sun, from the APOGEE, GALAH and Gaia surveys. We look for chemical and dynamical properties of these stars that give insights into their possible origin in the inner Galaxy. From their (Vphi ,VR) distribution, some of these metal-rich stars are associated with the Hercules moving group of stars, trapped by the Galactic bar in stable orbits around the rotating bar’s L4 neutral point. These orbits carry the stars out into the solar neighborhood. Our Gaussian Mixture Model analysis supports this view.
As part of this study, we investigate the distribution of orbital actions (JR, Jphi, Jz) for about 3.9 million stars within 1 kpc from the Sun. Unlike the stars of near-solar abundance, we find no change of orbital eccentricity distribution with abundance for the metal-rich stars with [Fe/H] = 0.1 to 0.5. These stars have all had a common dynamical history since their birth in the inner Galaxy. |
