000003968 001__ 3968
000003968 005__ 20190128165336.0
000003968 0247_ $$2DOI$$a10.1093/mnras/sty1673
000003968 037__ $$aSCART-2019-0095
000003968 100__ $$aHajduk, M.
000003968 245__ $$aRadio observations of planetary nebulae: no evidence for strong radial density gradients
000003968 260__ $$c2018
000003968 520__ $$aRadio-continuum observations trace the thermal emission of ionized plasma in planetary nebulae and bring useful information regarding nebular geometries. A model of a homogeneous sphere or shell cannot fit the nebular spectra and brightness temperatures. Two alternative models have been proposed in the literature: the first consists of two homogeneous components, while the other is a model of a shell with a significant radial density gradient. On the other hand, a prolate ellipsoidal shell model can fit the surface-brightness distribution of selected objects successfully. We verify the existing models using data collected in radio surveys covering a wide range of frequencies. In about 50 per cent of cases a density gradient can be excluded and none of the remaining objects could be confirmed. None of the observed planetary nebulae shows a spectral index of 0.6 in the optically thick part of the spectrum, which is the value predicted for a shell containing a strong radial density gradient. Radio spectra can be fitted with a model of a prolate ellipsoidal shell, but also by a shell containing temperature variations in planetary nebulae. At least eight planetary nebulae show two-component spectra, with one compact component showing much higher optical thickness than the other. Unexpectedly, the group of planetary nebulae with the lowest surface brightness shows non- negligible optical thickness. Their emission comes from compact and dense structures, comprising only a small part of the total nebular mass.
000003968 594__ $$aNO
000003968 6531_ $$aplanetary nebulae: general
000003968 6531_ $$aradio continuum: general
000003968 6531_ $$astars: AGB and post-AGB
000003968 6531_ $$astars: winds
000003968 6531_ $$aoutflows
000003968 6531_ $$aAstrophysics - Astrophysics of Galaxies
000003968 6531_ $$aAstrophysics - Solar and Stellar Astrophysics
000003968 700__ $$avan Hoof, P. A. M.
000003968 700__ $$aŚniadkowska, K.
000003968 700__ $$aKrankowski, A.
000003968 700__ $$aBłaszkiewicz, L.
000003968 700__ $$aDąbrowski, B.
000003968 700__ $$aZijlstra, A. A.
000003968 773__ $$c5657-5677$$n4$$pMonthly Notices of the Royal Astronomical Society$$v479$$y2018
000003968 8560_ $$fpeter.vanhoof@observatoire.be
000003968 85642 $$ahttps://ui.adsabs.harvard.edu/\#abs/2018MNRAS.479.5657H
000003968 905__ $$apublished in
000003968 980__ $$aREFERD