Analysis of high spatial resolution VLA images shows that the free-free emission from NGC 7538 IRS 1 is dominated by a collimated ionized wind .
We have re-analyzed high angular resolution VLA archive data from 6 cm to 7 mm , and measured separately the flux density from the compact bipolar core and the extended ( 1 ^ { \prime \prime } \hskip { -7.6 pt } . 5 - 3 ^ { \prime \prime } ) lobes .
We find that the flux density of the core is \propto \nu ^ { \alpha } , where \nu is the frequency and \alpha is \sim 0.7 .
The frequency dependence of the total flux density is slightly steeper with \alpha = 0.8 .
A massive optically thick hypercompact core with a steep density gradient can explain this frequency dependence , but it can not explain the extremely broad recombination line velocities observed in this source .
Neither can it explain why the core is bipolar rather than spherical , nor the observed decrease of 4 % in the flux density in less than 10 years .
An ionized wind modulated by accretion is expected to vary , because the accretion flow from the surrounding cloud will vary over time .
BIMA and CARMA continuum observations at 3 mm show that the free-free emission still dominates at 3 mm .
HCO ^ { + } J = 1 \to 0 observations combined with FCRAO single dish data show a clear inverse P Cygni profile towards IRS 1 .
These observations confirm that IRS 1 is heavily accreting with an accretion rate \sim 2 10 ^ { -4 } M _ { \odot } /yr .