NGC7538 IRS1 -- an O star driving an ionized jet and giant N-S outflow

TL;DR

This study characterizes the properties of the young O star NGC 7538 IRS 1, revealing its large outflow, ionized jet, and high accretion rate, which influence its evolution and the surrounding environment.

Contribution

It provides detailed multi-wavelength observations and analysis of IRS 1's outflow, jet, and accretion processes, highlighting the star's growth in a dense environment.

Findings

IRS 1 is a single O-star with luminosity > 10^5 Lsun

The outflow extends ~3.6 pc with a mass of ~130 Msun

Mass outflow rate matches the accretion rate of ~10^-3 Msun/yr

Abstract

NGC 7538 IRS 1 is a very young embedded O star driving an ionized jet and accreting mass with an accretion rate > 10^-4 Msun/year, which is quenching the hypercompact HII region. We use SOFIA GREAT data, Herschel PACS and SPIRE archive data, SOFIA FORCAST archive data, Onsala 20m and CARMA data, and JCMT archive data to determine the properties of the O star and its outflow. IRS 1 appears to be a single O-star with a bolometric luminosity > 1 10^5 Lsun, i.e. spectral type O7 or earlier. We find that IRS 1 drives a large molecular outflow with the blue-shifted northern outflow lobe extending to ~ 280" or 3.6 pc from IRS 1. Near IRS 1 the outflow is well aligned with the ionized jet. The dynamical time scale of the outflow is ~ 1.3 10^5 yr. The total outflow mass is ~ 130 Msun. We determine a mass outflow rate of 1.0 10^-3 Msun/yr, roughly consistent with the observed mass accretion rate. We observe strong high velocity [CII] emission in the outflow, confirming that strong UV radiation from IRS 1 escapes into the outflow lobes and is ionizing the gas. Many O stars may form like low mass stars, but with a higher accretion rate and in a denser environment. As long as the accretion stays high enough to quench the HII region, the star will continue to grow. When the accretion rate drops, the HII region will rapidly start to expand.