The determination of the mass of a Magellanic Cloud planetary nebula by speckle interferometry.

A Magellanic Cloud planetary nebula is resolved by speckle interferometry for the first time. The observations of SMC N2 show it to have a double-ring structure, the rings having angular radii of 0.22 and 0.38 arcsec, corresponding to absolute radii of 0.06 and 0.10 pc. The speckle observations of the galactic planetary nebula Vy 2-2 show a ring of angular diameter 0.4 arcsec, in agreement with previous VLA radio data. The radial hydrogen density profile for SMC N2 is determined and masses of 0.09 solar mass and 0.27 solar mass for the inner and outer shells respectively are derived, so that the total mass of this optically thin nebula is 0.36 solar mass. The nebular expansion velocity of SMC N2 has been derived from a high-resolution spectrum of the forbidden line O III 5007 A line and expansion ages of between 5000 and 12,000 yr have been derived for the shells. A reanalysis of the available nebular data leads to the derivation of a central star effective temperature of 110,000 K and a luminosity of 4340 solar luminosities, corresponding to a stellar mass of 0.59 solar mass, from a comparison with published evolutionary tracks. The stellar evolutionary age since leaving the asymptotic giant branch is about 8000 yr, consistent with the nebublar expansion age.