An analysis of the observed radio emission from planetary nebulae

Free access article

Issue		A&A Volume 373, Number 3, July III 2001


Page(s)		1032 - 1042
Section		Diffuse matter in space
DOI		http://dx.doi.org/10.1051/0004-6361:20010664

A&A 373, 1032-1042 (2001)
DOI: 10.1051/0004-6361:20010664

An analysis of the observed radio emission from planetary nebulae

N. Siódmiak and R. Tylenda

N. Copernicus Astronomical Center, Department for Astrophysics, Rabianska 8, 87-100 Torun, Poland Torun Center for Astronomy, N. Copernicus University, Gagarina 11, 87-100 Torun, Poland
e-mail: tylenda@ncac.torun.pl

(Received 20 June 2000 / Accepted 12 April 2001 )

Abstract
We have analysed the radio fluxes for 264 planetary nebulae for which reliable measurements of fluxes at 1.4 and 5 GHz, and of nebular diameters are available. For many of the investigated nebulae, the optical thickness is important, especially at 1.4 GHz. Simple models like the one specified only by a single optical thickness or spherical, constant density shells do not account satisfactorily for the observations. Also an r^-2 density distribution is ruled out. A reasonable representation of the observations can be obtained by a two-component model having regions of two different values of optical thickness. We show that the nebular diameters smaller than $10\arcsec$ are uncertain, particularly if they come from photographic plates or Gaussian fitting to the radio profile. While determining the interstellar extinction from an optical to radio flux ratio, caution should be paid regarding optical thickness effects in the radio. We have developed a method for estimating the value of self absorption. At 1.4 GHz self absorption of the flux is usually important and can exceed a factor of 10. At 5 GHz self absorption is negligible for most of the objects, although in some cases it can reach a factor of 2. The Galactic bulge planetary nebulae when used to calibrate the Shklovsky method give a mean nebular mass of $0.14 M_{\odot}$ . The statistical uncertainty of the Shklovsky distances is smaller than a factor of 1.5.

Key words: planetary nebulae: general -- radio continuum: ISM -- ISM: dust, extinction

Offprint request: N. Siódmiak, alexan@ncac.torun.pl

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