[Paper Review] 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

R. Hoogerwerf, J. H. J. de Bruijne+1 more|ArXiv.org|Oct 2, 2000

Stellar, planetary, and galactic studies90 references203 citations

TL;DR

This study uses high-precision astrometry from Hipparcos and radio observations to trace the trajectories of 56 runaway stars and nine pulsars within 700 pc, identifying their parent stellar groups. It confirms two key binary-supernova ejection events: ζ Ophiuchi and PSR J1932+1059 originated from a supernova in Upper Scorpius ~1 Myr ago, and AE Aur and μ Col were ejected from the Trapezium cluster ~2.5 Myr ago, providing strong kinematic evidence for the binary-supernova and dynamical ejection scenarios.

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.

Motivation & Objective

• To identify the parent stellar groups of high-velocity O and B-type stars (runaways) within 700 pc of the Sun using precise astrometric data.
• To test the binary-supernova scenario (BSS) and dynamical ejection scenario (DES) as origins for runaway stars and pulsars.
• To determine the kinematic ages and ejection mechanisms of runaways by reconstructing their orbital paths backward in time.
• To improve the identification of parent associations for pulsars and runaway stars, especially those with high peculiar velocities.
• To assess the impact of runaway ejection on the initial mass function of young stellar groups by quantifying mass loss during ejection events.

Proposed method

• Utilized milli-arcsecond accuracy astrometry (proper motions and parallaxes) from the Hipparcos satellite and radio very-long-baseline interferometry (VLBI) for precise stellar position and motion measurements.
• Reconstructed backward orbital trajectories of 56 runaway stars and nine compact objects using Galactic potential models and numerical integration.
• Applied kinematic age estimation by calculating the time since ejection based on the distance traveled and velocity vector, assuming constant motion.
• Correlated the backward-traced positions with known young stellar associations and open clusters (e.g., Sco OB2, Per OB3, Trapezium cluster) to identify parent groups.
• Evaluated the consistency of ejection scenarios by checking whether the three-body system (runaway, companion, and compact object) occupied a small spatial volume at the time of ejection.
• Used statistical analysis to assess the bias toward identifying recent BSS runaways due to distance and age limits, and to estimate the fraction of runaways originating from dynamical ejections vs. supernova ejections.

Experimental results

Research questions

• RQ1 Can the parent stellar group of a runaway star or pulsar be identified with high confidence using high-precision astrometry?
• RQ2 What is the origin of the high-velocity star ζ Ophiuchi and its associated pulsar PSR J1932+1059?
• RQ3 Do the runaway stars AE Aur and μ Col share a common origin with the binary system ι Ori, as previously hypothesized?
• RQ4 What fraction of the 56 runaways within 700 pc can be linked to known young stellar groups or associations?
• RQ5 How do the kinematic ages of runaways compare with the ages of their putative parent groups, and what does this imply for the ejection mechanism?

Key findings

• The runaway star ζ Ophiuchi and the pulsar PSR J1932+1059 originated from a supernova explosion in a binary system in the Upper Scorpius subgroup of Sco OB2 approximately 1 million years ago.
• The pulsar received a kick velocity of approximately 350 km s⁻¹ during the supernova explosion, which disrupted the binary and ejected ζ Oph with a high space velocity.
• AE Aur and μ Col were ejected from the nascent Trapezium cluster ~2.5 million years ago, with their velocities and positions consistent with a common origin involving the massive binary ι Ori.
• Twenty-one of the 56 runaways in the sample can be definitively linked to nearby associations and young open clusters, including classical runaways like 53 Arietis, ξ Persei, and λ Cephei.
• Two additional pulsars (J0826+2637 and J1115+5030) are likely associated with the 50 Myr-old Per OB3 association, which includes the open cluster α Persei.
• The study triples the number of known runaways with identified parent groups, increasing the count from 6 to 21 within 700 pc, and confirms the dominance of the binary-supernova scenario for recent ejections.