... interferometry

Observations reported here were obtained at the MMT Observatory, a joint facility of the Smithsonian Institution and the University of Arizona, and at the BTA 6 m telescope of the Special Astrophysical Observatory, Russia. In addition, this work is based in part on archival data obtained with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA.

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... PA

Following the convention, we measure the position angle (PA) from north to east.

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... field

The K-band luminosity function by Balog et al. (2004) for the whole NGC 7538 region, corrected with the on-cluster KLF, and cumulated for the magnitude range 11 $.\!\!^{\rm m}$0 to 12 $.\!\!^{\rm m}$0 was used.

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... errors

The astrometric accuracy of the 2MASS catalogue was reported to be $\sim$ $0\hbox{$.\!\!^{\prime\prime}$ }15$ (see http://ipac.caltech.edu/2mass/releases/allsky/doc/expl-sup.html).

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... negligible

Interestingly, the converse assumption (that disk warping is non-negligible) implies disk precession as well, as the jet would be launched perpendicular to the warped surface of the inner part of the disk.

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... observer

This is consistent with the precession parameters determined in Sect. 4.4.3, where we find that the half-opening angle of the precession $\Theta$ is larger than the inclination of the precession axis with respect to the plane of the sky $\psi$.

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... sky

Positive values of $\psi$ indicate an inclination out of the plane of the sky towards the observer.

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... counter-clockwise

For the sense of rotation, we follow the convention that counter-clockwise rotation (as measured from the source along the precession axis) corresponds to a positive sign of the phase $\phi$.

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