The structure of NGC 3587, the Owl nebula.

Long-slit echelle spectra at various position angles of the faint, extended planetary nebula NGC 3587 (the Owl nebula) are used to study the kinematical properties of the gas in the brighter nebular emission lines (forbidden O III, H-alpha and forbidden N II). The main part of the nebula consists of an inhomogeneous shell, whose density and thickness are larger in a plane passing through the two bright condensations which are visible in the photographs of this object (at pa = 30 deg). Observational evidence is presented indicating that the nebula is close to the thick-thin transition, that its total nebular mass is about 0.15 solar masses and that its central star has a mass of about 0.70 solar masses.