On the origin of the O and B-type stars with high velocities II Runaway stars and pulsars ejected from the nearby young stellar groups

TL;DR

This study traces the origins of high-velocity O and B-type stars and pulsars within 700 pc, identifying their parent stellar groups and formation scenarios using precise astrometry, revealing multiple ejection events from young clusters.

Contribution

It provides new identifications of parent groups for runaway stars and pulsars, and confirms specific supernova and cluster ejection origins with high-precision astrometry.

Findings

Identified parent groups for 21 runaway stars and 2 pulsars.

Confirmed supernova origin for zeta Ophiuchi and PSR J1932+1059.

Demonstrated ejection from the Trapezium cluster for AE Aur, mu Col, and iota Ori.

Abstract

We use milli-arcsecond accuracy astrometry (proper motions and parallaxes) from Hipparcos and from radio observations to retrace the orbits of 56 runaway stars and nine compact objects with distances less than 700 pc, to identify the parent stellar group. It is possible to deduce the specific formation scenario with near certainty for two cases. (i) We find that the runaway star zeta Ophiuchi and the pulsar PSR J1932+1059 originated about 1 Myr ago in a supernova explosion in a binary in the Upper Scorpius subgroup of the Sco OB2 association. The pulsar received a kick velocity of about 350 km/s in this event, which dissociated the binary, and gave zeta Oph its large space velocity. (ii) Blaauw & Morgan and Gies & Bolton already postulated a common origin for the runaway-pair AE Aur and mu Col, possibly involving the massive highly-eccentric binary iota Ori, based on their equal and opposite velocities. We demonstrate that these three objects indeed occupied a very small volume \sim 2.5Myr ago, and show that they were ejected from the nascent Trapezium cluster. We identify the parent group for two more pulsars: both likely originate in the 50 Myr old association Per OB3, which contains the open cluster alpha Persei. At least 21 of the 56 runaway stars in our sample can be linked to the nearby associations and young open clusters. These include the classical runaways 53 Arietis (Ori OB1), xi Persei (Per OB2), and lambda Cephei (Cep OB3), and fifteen new identifications, amongst which a pair of stars running away in opposite directions from the region containing the lambda Ori cluster. Other currently nearby runaways and pulsars originated beyond 700 pc, where our knowledge of the parent groups is very incomplete.