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Some Recent Results from UV Observations [chapter]

M. J. Seaton
1983 Planetary Nebulae  
UV observations with IUE have led to recognition of the importance of di-electronic recombination in PN, for the calculation of ionization equilibria and for production of the features C II X1335 and C III X2297. The determination of C abundances is discussed. In high-excitation nebulae one must allow for absorption of C IV X154-9 by dust. It has been shown that C/0 < 0.5 for five PN with a silicate IR feature and that C/0 > 1 for four with a SiC feature. Dust opacities T n have been deduced
more » ... ave been deduced from observed ratios (C IV X1549)/(C III X2297) and (C II X1335)/(C I X«67) . The values obtained, T^ -0.1, are consistent with the observed strength of thermal infra-red emission. Earlier UV observations of PN were made by Pottasch et al. (1978) using ANS. Results obtained using IUE support neither their downward revisions of star temperatures nor their claim that a number of stars with T z (He II) » T Z (H I) are optically thick for H I. From IUE observations it is concluded that the planetary K 64-8 in M 15 has C/0 = 2 A and that its central star has a temperature of 30 000 K and a luminosity of 1700 L 0 . The present contribution is concerned with some IUE work with which I have been associated but makes no attempt at a comprehensive review of IUE observations of planetary nebulae. 129 D. R. Flower fed.), Planetary Nebulae, 129-139.
doi:10.1007/978-94-009-7094-6_15 fatcat:3dgeg3hmuvbtfgu23pkc64qple