Encounters and Close Fly-Bys of Galactic Clusters and Associations in the Past 50 Myr

Abstract

Collisions and close fly-bys of molecular clouds and associations may be an important mechanism of star formation in the solar neighborhood. A giant molecular cloud may be directly impacted by the gas in another cloud upon a cloud-cloud collision (Lépine & Duvert 1994) or it may be shocked by bubbles blown up by stellar winds and supernova explosions in a chance fly-by OB association (de Geus 1991). Clues of such events during the last 50 Myr are sought for ∼ 80 nearby open clusters, OB associations and star forming regions using the epicycle approximation of the Galactic orbital motion. Several possible events are identified, and their times, relative velocities and impact distances are estimated. In some cases, the events are more recent than the assumed age of one of the parties involved, e.g., the possible encounter of the Coma cluster with the Taurus-Auriga star forming region 10 Myr ago. In other cases, the estimated time of the event matches fairly well the isochrone ages of both parties, e.g., the encounter of the LCC and IC 2602, 36 Myr ago. Relative velocities found thus far are between 5 and 20 km s ⁻¹.