Abstract

Contributed Talk - Splinter StarFormation   (MW-1250)

Flying the nest: using 4MOST to explore the origins of nearby young runaway stars

Alex Binks (1), Beate Stelzer (1), Germano Sacco (2)
(1) Universität Tübingen, (2) INAF, Osservatorio di Arcetri

The vast majority of stars are born in clusters, but by ~10-100 Myr most have been scattered from their star forming regions (SFRs) into the Galactic field, and are spread all over the sky. Suggested mechanisms for cluster dispersal include gas expulsion, 3-body (binary) interactions, mass segregation and even supernovae blast waves. To test these theories, we need to identify young runaway (RW) stars that have been recently ejected from their SFR and trace back their Galactic orbits to determine their birthsites and possible ejection mechanisms. This requires accurate 3D spatio-kinematic data, and some unambiguous stellar youth determinant. Although Gaia has provided a monumental leg-up by providing high-precision 3D positions and 2D tangential velocities for tens of thousands of candidate RWs out to ~1 kpc, line-of-sight radial velocities (RVs) are severely lacking and urgently require spectroscopic follow-up. This sets the stage for the 4MOST Survey of Young Stars (4SYS), a spectroscopic catalogue of ~200k iso- and gyro- chronally selected young stars within 500 pc. Our sample is free from any spatial or kinematic bias, meaning we can identify young stars all over the Southern hemisphere. With ~2400 optical fibres, distributed over a 4-degree field of view, 4MOST will gradually observe our sample over the next 5 years, providing an RV precision below 1 km/s and lithium abundances to unambiguously confirm youth and constrain stellar ages. By studying the chemo-dynamics of young 4SYS stars, we will detect thousands of RWs, determine their spatial and chemical origins, and investigate smoking-gun causes of dispersal. Results from 4SYS will improve our understanding of how SFRs evolve and disperse, and connects studies of the local star forming rate and origin of our nearest stars to constraints at larger (extra)Galactic scales. In this talk I provide an overview of 4SYS along with some (very) preliminary results from early science observations.