Schematic cartoon illustrating several crucial features of NGC 7538 IRS1 that are discussed in the text. 6.7 GHz CH3OH masers observed with the EVN (filled circles) identify two high-mass YSOs, IRS1a and IRS1b, surrounded by (quasi-)edge-on disks. The black ellipses represent the disk planes, with the solid lines indicating the near-side and the dashed lines the far-side of the disks. These star-disk systems reside in the inner cavity of the circumbinary envelope (probed by hot ammonia), cleared up by the orbital motion of the binary members. The cartoon shows only the central section of such a molecular envelope (supposedly spherical). The gas in the envelope may feed the circumstellar disks of IRS1a/b (this is however of too high-order complexity to be shown). Colors denote line-of-sight velocities, with blue indicating blueshifted emission and red indicating redshifted emission, while green represents systemic velocity. Material in both the disks and the envelope is rotating, in the sense indicated by the black arrows.
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