Angular dimensions of planetary nebulae^*

¹ N. Copernicus Astronomical Center, Department for Astrophysics, Rabiańska 8, 87–100 Toruń, Poland
² Isaac Newton Group of Telescopes, Apartado de Correos 321, 38700 Sta. Cruz de La Palma, Spain
³ CTIO/NOAO, Casilla 603, La Serena, Chile

Corresponding author: N. Siódmiak, alexan@ncac.torun.pl

Received: 28 May 2002
Accepted: 23 April 2003

Abstract

We have measured angular dimensions of 312 planetary nebulae from their images obtained in Hα (or Hα + [NII]). We have applied three methods of measurements: direct measurements at the 10% level of the peak surface brightness, Gaussian deconvolution and second-moment deconvolution. The results from the three methods are compared and analysed. We propose a simple deconvolution of the 10% level measurements which significantly improves the reliability of these measurements for compact and partially resolved nebulae. Gaussian deconvolution gives consistent but somewhat underestimated diameters compared to the 10% measurements. Second-moment deconvolution gives results in poor agreement with those from the other two methods, especially for poorly resolved nebulae. From the results of measurements and using the conclusions of our analysis we derive the final nebular diameters which should be free from systematic differences between small (partially resolved) and extended (well resolved) objects in our sample.