Search for OB stars running away from young star clusters. I. NGC 6611

TL;DR

This study uses infrared survey data to identify bow shocks around OB stars, providing evidence that young star clusters like NGC 6611 can lose a significant number of their massive stars early in their evolution.

Contribution

The paper reports the discovery of three bow shocks from O-type stars ejected from NGC 6611, supporting the idea of early dynamical loss of OB stars from young clusters.

Findings

Discovered multiple bow shocks around OB stars near young clusters.

Confirmed ejection of O-type stars from NGC 6611.

Supported the hypothesis of early dynamical loss of OB stars.

Abstract

N-body simulations have shown that the dynamical decay of the young (~1 Myr) Orion Nebula cluster could be responsible for the loss of at least half of its initial content of OB stars. This result suggests that other young stellar systems could also lose a significant fraction of their massive stars at the very beginning of their evolution. To confirm this expectation, we used the Mid-Infrared Galactic Plane Survey (completed by the Midcourse Space Experiment satellite) to search for bow shocks around a number of young ($\la$ several Myr) clusters and OB associations. We discovered dozens of bow shocks generated by OB stars running away from these stellar systems, supporting the idea of significant dynamical loss of OB stars. In this paper, we report the discovery of three bow shocks produced by O-type stars ejected from the open cluster NGC6611 (M16). One of the bow shocks is associated with the O9.5Iab star HD165319, which was suggested to be one of "the best examples for isolated Galactic high-mass star formation" (de Wit et al. 2005, A&A, 437, 247). Possible implications of our results for the origin of field OB stars are discussed.