THE SUN WAS NOT BORN IN M67

Abstract

Using the most recent proper-motion determination of the old,\nSolar-metallicity, Galactic open cluster M 67, in orbital computations in a\nnon-axisymmetric model of the Milky Way, including a bar and 3D spiral arms, we\nexplore the possibility that the Sun once belonged to this cluster. We have\nperformed Monte Carlo numerical simulations to generate the present-day orbital\nconditions of the Sun and M 67, and all the parameters in the Galactic model.\nWe compute 3.5 \\times 10^5 pairs of orbits Sun-M 67 looking for close\nencounters in the past with a minimum distance approach within the tidal radius\nof M 67. In these encounters we find that the relative velocity between the Sun\nand M 67 is larger than 20 km/s. If the Sun had been ejected from M 67 with\nthis high velocity by means of a three-body encounter, this interaction would\ndestroy an initial circumstellar disk around the Sun, or disperse its already\nformed planets. We also find a very low probability, much less than 10^-7, that\nthe Sun was ejected from M 67 by an encounter of this cluster with a giant\nmolecular cloud. This study also excludes the possibility that the Sun and M 67\nwere born in the same molecular cloud. Our dynamical results convincingly\ndemonstrate that M67 could not have been the birth cluster of our Solar System.\n