Computer Science
Scientific paper
Jul 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992hst..prop.3608c&link_type=abstract
HST Proposal ID #3608
Computer Science
Hst Proposal Id #3608
Scientific paper
Abundances of C,N and O in red giant stars and planetary nebulae (PNs) provide important diagnostics of stellar evolution theory. CNO isotope ratios (eg 12C/13C, 15N/14N and 16O/18O) have given many extra constraints on all the mixing processes occurring between the main sequence and PN ejection. In general, observations show more mixing occurs than is predicted. The CNO abundances for Galactic and Magellanic Cloud PNs show that the '3rd dredge-up' of 12C is more efficient in metal-poor environments. However, until now it has not been possible to measure important diagnostics such as the 12C/13C ratio in nebulae so as to relate red giant & PN populations. We propose to use the GHRS, Echelle and Large Science Aperture to measure C12/13 ratios in 3 PNs with a novel spectroscopic method. As 12C has zero nuclear spin, the normal C III 1S(J=F=0) - 3P(J=F=0,1,2) transition has only two components (1906.7, 1908.7A). But the nuclear spin (I=1/2) of 13C gives a finite line strength to an F=1/2-1/2 transition at 1909.6A, which is absent in 12C. Measurement of all three lines will provide the C12/13 ratio. In an allocation of under 9 hours we can reach 3-4 sigma limits for a C-rich Galactic nebula, a C-rich SMC nebula, and a Type I (He and N-rich, and having C
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