How do we know that Antares is a halo star?
You can tell that a star is a halo star by its trajectory, and its stellar type. Halo stars, most of which were formed very early in the Galaxy’s history, can have all kinds of roughly elliptical orbits around the Galactic center. Their orbits can be very tilted with respect to the Galactic plane, and they can cruise on through the disk (rarely colliding with disk stars, though, because the typical size of of a star is very small compared to the typical distance between stars). A star in our neighborhood which is not moving along with the Milky Way disk (for instance, which has a large velocity relative to nearby stars, or which has a “retrograde motion” with respect to the general rotation) is probably a halo star, since disk stars tend to rotate around with the disk. Stars which are old, and have few “metals” (heavy elements) and therefore probably went through very few star-supernova-gas-star cycles, also match the typical profile of halo star. Actually when poking around for de
