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The determination of the mass of a Magellanic Cloud planetary nebula by speckle interferometry
A Magellanic Cloud planetary nebula is resolved by speckleinterferometry for the first time. The observations of SMC N2 show it tohave a double-ring structure, the rings having angular radii of 0.22 and0.38 arcsec, corresponding to absolute radii of 0.06 and 0.10 pc. Thespeckle observations of the galactic planetary nebula Vy 2-2 show a ringof angular diameter 0.4 arcsec, in agreement with previous VLA radiodata. The radial hydrogen density profile for SMC N2 is determined andmasses of 0.09 solar mass and 0.27 solar mass for the inner and outershells respectively are derived, so that the total mass of thisoptically thin nebula is 0.36 solar mass. The nebular expansion velocityof SMC N2 has been derived from a high-resolution spectrum of theforbidden line O III 5007 A line and expansion ages of between 5000 and12,000 yr have been derived for the shells. A reanalysis of theavailable nebular data leads to the derivation of a central stareffective temperature of 110,000 K and a luminosity of 4340 solarluminosities, corresponding to a stellar mass of 0.59 solar mass, from acomparison with published evolutionary tracks. The stellar evolutionaryage since leaving the asymptotic giant branch is about 8000 yr,consistent with the nebublar expansion age.
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