Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993rmxaa..27..157k&link_type=abstract
Revista Mexicana de Astronomia y Astrofisica, 27, 157
Astronomy and Astrophysics
Astronomy
1
Scientific paper
RESUMEN Se presantan abundancias element ales para una muestra de 70 nebulosas planetarias (NP) galacticas del sur, basadas en observaciones opticas y ultrovioleta. En esta muestra, se clasifican solidamente 6 objetos Tipo I. Para las NP Tipo I, no se encuentran de agotamentio de oxygen comparando con NP que no son de Tipo I, por tanto el ciclo ON que operar durante la 2a fase de dragado no afecta significativamente las abundancias superficiales de la estrella progenitora. Para las NP que no son Tipo I, se encuentra que la conversion de carbon a nitrogeno durante la 1a fase de dragado es suficiente por explicar el aumento en abundancia de nitrogeno en regiones 1111. Una comparison entre abundancias de nitrogeno en NP y abundancias de carbon+nitrogeno en regiones 1111 galacticas indica que aproximadamente 30% del carbon inicial es convirtido en nitrogeno por las NP que no son Tipo I. Sin embargo, explicar las altas abundancias de nitrogeno en las NP Tipo I, el quemado de la envolvente convectiva durante la 3a fase de dragado es necesario. Abundancias totales CtN+O se correlacionan con C/H para la muestra combinanda de Tipo I y no-Tipo I; Ia abundancia de carbon se incrementa via quemado de helio y subsecuentemente los productos son traidos a la superficie en el 3a fase de dragado. ABSTRACT We present elemental abundances for a sample of 70 southern Galactic planetary nebulae (PN), based on observations at both UV and optical wavelengths. In this sample, 6 definite Type I objects are identified. For the Type I PN, no evidence for oxygen depletion compared to non-Type I PN is found, hence the ON cycle which operates in the 2nd dredge up does not significantly affect the surface abundances of the progenitor star. For the non-Type I PN, we find that the conversion of carbon into nitrogen during the first dredge-up phase is sufficient to account for the increase in nitrogen abundances over 1111 regions. A comparison between nitrogen abundances in PN and carbon+nitrogen abundances in Galactic 1111 regions indicates that roughly 30% of the initial carbon is converted into nitrogen for the non-Type I PN. However, in order to explain the high nitrogen abundances derived for Type I PN, convective envelope burning during the 3rd dredge-up phase is required. Total C+N+O abundances are found to be correlated with C/H for the combined non-Type I and Type I sample; the carbon abundance is increased via He-burning, the products of which are subsequently brought to the surface by the 3rd dredge-up. Key words: PLANETARY NEBULAE: GENERAL
Barlow Michael J.
Kingsburgh Robin L.
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