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