1.5 y cavidades centrales con radios menores que el 20% del radio externo de la envolvente.]]>
10 20% of PNe probably do contain gradients. We now extend this latter analysis to include significantly higher frequency fluxes, and use these to undertake a more sensitive analysis of the effects of radial density gradients. We conclude than in excess of 85% of PNe appear to contain gradients, of which 21% are likely to have density exponents β > 1.5, and central cavity sizes which are small (i.e. have radii < 20% of the outer radius of the shell).]]>
Revista mexicana de astronomía y astrofísica
A 1.4 GHZ and 14.7 GHZ analysis of density gradients in galactic planetary nebulae
J. P. Phillips
Instituto de Astronomía y Meteorología Universidad de Guadalajara, México
John P. Phillips: Instituto de Astronomía y Meteorología, Universidad de Guadalajara, Av. Vallarta No. 2602, Col. Arcos Vallarta, 44130 Guadalajara, Jalisco, México (jpp@astro.iam.udg.mx).
Received 2007 March 21 ]]>
Accepted 2007 May 30
Resumen
Actualmente hay una considerable incertidumbre acerca de la existencia de gradientes radiales de densidad en Nebulosas Planetarias (NPs). Si bien el trabajo de Taylor et al. (1987) implica la existencia de gradientes de densidad en la mayoría de las planetarias, el de Siódmiak & Tylenda (2001) sugiere precisamente lo contrario. El trabajo de Phillips (2007) sugiere que ambos análisis son dudosos y que al menos en un 10 a 20% de las NPs existen, probablemente, estos gradientes.
En este trabajo extendemos este último análisis para incluir flujos en frecuencias mayores y los utilizamos para llevar a cabo un análisis más sensible de los efectos de los gradientes radiales de densidad. Concluimos que en más del 85% de las NPs parecen existir gradientes de densidad, el 21% de los cuales tienen probablemente un exponente β > 1.5 y cavidades centrales con radios menores que el 20% del radio externo de la envolvente.
Abstract
There has been a considerable level of uncertainty as to whether planetary nebulae (PNe) contain radial density gradients. Whilst the work of Taylor et al. (1987) implies that gradients exist in most PNe, that of Siódmiak & Tylenda (2001) suggests precisely the reverse. The work of Phillips (2007) suggests that both of these analyses are suspect, however, and that at least 10 20% of PNe probably do contain gradients.
We now extend this latter analysis to include significantly higher frequency fluxes, and use these to undertake a more sensitive analysis of the effects of radial density gradients. We conclude than in excess of 85% of PNe appear to contain gradients, of which 21% are likely to have density exponents β > 1.5, and central cavity sizes which are small (i.e. have radii < 20% of the outer radius of the shell).
Key Words: ISM: jets and outflows—planetary nebulae:general
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20% of PNe probably do contain gradients. We now extend this latter analysis to include significantly higher frequency fluxes, and use these to undertake a more sensitive analysis of the effects of radial density gradients. We conclude than in excess of 85% of PNe appear to contain gradients, of which 
21% are likely to have density exponents β > 1.5, and central cavity sizes which are small (i.e. have radii < 20% of the outer radius of the shell).]]>
10 
20% of PNe probably do contain gradients.