# Proper motions of five OB stars with candidate dusty bow shocks in the Carina Nebula

## TL;DR

This study measures the proper motions of five OB stars with candidate bow shocks in the Carina Nebula using HST data, revealing that these shocks are often shaped by ambient gas flows rather than stellar motion, and suggesting in-situ star formation.

## Contribution

First direct proper motion measurements of OB stars with candidate bow shocks in Carina, clarifying the origins of observed bow shocks and the formation history of the region.

## Key findings

- Stars are not runaway stars; their motions do not point away from the nebula's center.
- Large-scale gas flows influence the shape of bow shocks more than stellar motion.
- Stars' motions suggest in-situ formation rather than migration from central clusters.

## Abstract

We constrain the proper motions of five OB stars associated with candidate stellar wind bow shocks in the Carina Nebula using HST ACS imaging over 9--10 year baselines. These proper motions allow us to directly compare each star's motion to the orientation of its candidate bow shock. Although these stars are saturated in our imaging, we assess their motion by the shifts required to minimize residuals in their Airy rings. The results limit the direction of each star's motion to sectors less than 90 degrees wide. None of the five stars are moving away from the Carina Nebula's central clusters as runaway stars would be, confirming that a candidate bow shock is not necessarily indicative of a runaway star. Two of the five stars are moving tangentially relative to the orientation of their candidate bow shocks, both of which point at the OB cluster Trumpler 14. In these cases, the large-scale flow of the interstellar medium, powered by feedback from the cluster, appears to dominate over the motion of the star in producing the observed candidate bow shock. The remaining three stars all have some component of motion toward the central clusters, meaning that we cannot distinguish whether their candidate bow shocks are indicators of stellar motion, of the flow of ambient gas, or of density gradients in their surroundings. In addition, these stars' lack of outward motion hints that the distributed massive-star population in Carina's South Pillars region formed in place, rather than migrating out from the association's central clusters.