Interstellar CNO Isotope Ratios

Interstellar CNO Isotope Ratios

C. Henkel
Max-Planck-Institut für Radioastronomie
Auf dem Hügel 69, D-53121 Bonn, Germany

T.L. Wilson
Max-Planck-Institut für Radioastronomie
Auf dem Hügel 69, D-53121 Bonn, Germany

N. Langer
Max-Planck-Institut für Astrophysik
Karl-Schwarzschild-Str. 1, D-85740 Garching, Germany

Y.-N. Chin
Radioastronomisches Institut der Universität Bonn
Auf dem Hügel 71, D-53121 Bonn, Germany

R. Mauersberger
Max-Planck-Institut für Radioastronomie
Auf dem Hügel 69, D-53121 Bonn, Germany

Paper appeared in The Structure and Content of Molecular Clouds (25 years of Molecular Radioastronomy) eds. T.L. Wilson and K.J. Johnston : a proceeding of a conference held at Schloß Ringberg, Tegenasee, Germany on April 14 - 16, 1993, pp. 72-88. If you want to have a look at the complete paper (without figures) please click here (PostScript file of 153238 bytes).

Abstract. In an interpretation of interstellar, circumstellar, and solar system CNO isotope ratios, we find two scenarios which are free of internal inconsistencies. The first requires that the early solar system was enriched by material from massive stars, leading to enhanced ¹²C/¹³C and ¹⁸O/¹⁷O ratios and to a reduced ¹⁴N/¹⁵N ratio. The second involves infall of gas onto the galactic disk after the formation of the solar system. Both scenarios require that the bulk of the interstellar ¹⁶O, ¹⁸O, and ¹⁵N originates from massive stars (> 8 solar mass), with ¹⁸O and perhaps ¹⁵N being destroyed in lower mass stars. ¹⁷O is mainly synthesized in stars of intermediate mass while ¹²C, ¹³C, and ¹⁴N are produced in stars of high and intermediate masses. With respect to nucleosynthesis, evolutionary models of massive stars applying the Ledoux criterion for convection and semiconvective mixing should be preferred. These yield high ¹⁸O abundances above the convective He-burning core. For ¹⁷O, theoretical yields and observational data are not consistent, since models predict too much ¹⁷O from massive stars. The absence of an ¹⁸O/¹⁷O gradient in the galactic plane remains unexplained. Since ¹⁸O and ¹⁷O are products of quite different processes, this absence strongly constrains numerical models of the `chemical' evolution of the Galaxy.

Any suggestion or comments please e-mail to einmann@asiaa.sinica.edu.tw.

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