The P Cygni supergiant [OMN2000] LS1 - implications for the star formation history of W51

TL;DR

This study characterizes the P Cygni supergiant [OMN2000] LS1 in W51, revealing insights into the region's star formation history, indicating ongoing massive star formation over at least 3 million years without sequential triggering.

Contribution

It provides the first detailed physical analysis of [OMN2000] LS1 and constrains the star formation timeline and mechanisms within the W51 complex.

Findings

[OMN2000] LS1 is a cooler, less luminous supergiant than previously thought.

Star formation in W51 has been ongoing for at least 3 million years.

Star formation likely occurred at multiple independent sites, not sequentially.

Abstract

We investigated the nature of the massive star [OMN2000] LS1 and used these results to constrain the history of star formation within the host complex W51. A combination of near-IR spectroscopy and non-LTE model atmosphere analysis was used to derive the physical properties of [OMN2000] LS1 and a combination of theoretical evolutionary calculations and Monte Carlo simulations to apply limits on the star formation history of W51. The spectrum of [OMN2000] LS1 is consistent with that of a P Cygni supergiant, but with a temperature of 13.2-13.7kK and log(L/L_sun)<5.75, it is significantly cooler, less luminous, and massive than proposed by previous authors. The presence of such a star within W51 shows that star formation has been underway for at least 3Myr, while the formation of massive O stars is still on going. We find no evidence of internally triggered, sequential star formation within W51, and favour the suggestion that star formation has proceeded at multiple indepedent sites within the GMC. [ABRIDGED]