The spectrum and structure of ''Minkowski's footprint'': M 1--92

M 1--92 is a small elliptical nebulosity of quite high surface brightness, discovered originally by Minkowski. It is divided unequally by a dark gap so as to have the appearance of a human footprint; the overall dimensions are about 4''.5times11''.5. On infrared photographs a faint red star appears in the gap between the two lobes. Both lobes show a broad-lined P Cygni spectrum with dark components displaced shortward to -530 km s-1, plus a sharp-line, low-excitation emission spectrum of H, Fe ii, Fe ii, Ti ii, Si i, etc., which gives a velocity of -15 km s-1 in the bright lobe and +17 km s-1 in the faint. Emission lines of O i, S ii, N ii are also present. The spectroscopic and photometric data can be explained if the emission spectrum observed in the nebulae actually originates near the central star, and is only scattered off dust being driven radially outward through the two lobes at a velocity of approximately 30 km s-1. The central star is believed to be surrounded by a dense, flattened, circumstellar dust disk and by a much larger and more tenuous cloud. Two independent estimates suggest an axial extinction in the bright lobe of A/subv/=3--4 mag; the total line-of-sight extinction of the star must be considerably larger. The two lobes are thus only the polar regions of the larger cloud, illuminated by the star through the relatively transparent poles of the flattened disk. A large infrared excess is also present; it presumably originates in the dense circumstellar disk very near the star. No changes have been observed in the structure of the nebula or in the total brightness. The evolutionary state of M 1--92 is unknown