Optical Spectroscopy of the Red Horizontal Branch Stars of NGC 6791

Details Optical Spectroscopy of the Red Horizontal Branch Stars of NGC 6791 Optical Spectroscopy of the Red Horizontal Branch Stars of NGC 6791

Aug 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995aj....110..693h&link_type=abstract

Astronomical Journal v.110, p.693

Astronomy and Astrophysics

Astronomy

7

Globular Clusters: Individual: Ngc 6791, Stars: Abundances

Scientific paper

We have obtained 3600-4600 Å spectra at ˜5 Å resolution for 31 stars in the field of NGC 6791, one of the oldest and most "globular-cluster-like" of the Galactic open clusters. Based on spectroscopic analysis of 19 of these stars considered to be red horizontal branch (RHB) members of NGC 6791, we conclude that there is no evidence for significant variations in the CR band or the Ca and Fe line strengths among these stars, although there are strong indications of intrinsic differences among the CN band strengths. There is also no evidence for correlations between the CN band, CR band, or Fe line strengths of these stars, although there may be a weak correlation between CN band and Ca line strengths. The nature of the CN-band inhomogeneity is in marked contrast to the bimodal CN distributions discovered among the RHB stars of the two globular clusters 47 Tuc and M71 by Norris & Freeman [ApJ, 254, 143 (1982)] and Smith & Penny [M, 97, 1397 (1989)]. These results imply that either the environment within which globular clusters formed resulted in initial C and N abundance inhomogeneities that were lacking in NGC 6791, or that the evolutional processes which alter stellar surface abundances prior to or during the core helium-burning phase of evolution, differ in some respect between the disk globular clusters and NGC 6791.

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