Open cluster chemical composition. 1: Later type stars in eight clusters

Details Open cluster chemical composition. 1: Later type stars in eight clusters Open cluster chemical composition. 1: Later type stars in eight clusters

Mar 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apjs...91..309l&link_type=abstract

Astrophysical Journal Supplement Series (ISSN 0067-0049), vol. 91, no. 1, p. 309-346

Astronomy and Astrophysics

Astrophysics

64

Abundance, Carbon, Cepheid Variables, G Stars, Iron, K Stars, Lithium, Nitrogen, Open Clusters, Oxygen, Sodium, Supergiant Stars, Tables (Data), Astronomical Models, Correlation, Echelle Gratings, Gravitational Effects, Spectrographs, Stellar Evolution, Stellar Mass, Turbulent Mixing

Scientific paper

Abundance analyses of 36 stars associated with eight open clusters (IC 2581, NGC 3532, NGC 5822, NGC 6067, NGC 6087, IC 4725 (M25), IC 4756, and NGC 6882/6885) are presented. The stars are primarily evolved G and K giants and supergiants. Cepheids in NGC 6067, NGC 6087, and IC 4725 are included as are non-cluster Cepheids near the clusters NGC 3532, NGC 6067, and IC 4725. With the addition of a background K giant in IC 4725, the total number of stars is 40. Elemental abundances derived include Li, C, N, O, the alpha-elements, the Fe peak, and limited data on the heavy elements. The Na abundances of the sample show a gravity dependence in the sense of an increase in the abundance as the gravity decreases. The CNO abundances indicate that these objects are processed (on the whole), and that they show the O deficiency previously noted in intermediate mass stars by Luck & Lambert (1981, 1985). There are four stars in the sample which appear to be unprocessed: two giants and two supergiants. There are also two super-Li stars in the sample, one of which is most likely a weak G-band star. It is suggested that the super-Li F supergiants could be evolved blue stragglers. The most striking result of the study is the finding that the (O/Na) ratio correlates strongly with the gravity and the stellar mass, thus implying that there is a nonstandard additional mixing process affecting the surface abundances of these stars. A promising candidate for the mixing process is the turbulent diffusive mixing process proposed by Denissenkov (1993) which brings Na to the surface and which could also lead to a modification of the oxygen content.

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