Abundance spread in the giants of NGC 6752

Journal Article · Sun Feb 15 04:00:00 EST 1981 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/158698· OSTI ID:6186133

Norris, J; Cottrell, P L; Freeman, K C; Da Costa, G S

A spectroscopic survey has been performed of 69 stars on or near the giant branches of the metal-poor globular cluster NGC 6752. Our basic results are: (i) There is a large range in the strength of the violet cyanogen bands on the red giant branch, with the available evidence strongly suggesting that the distribution is bimodal. (ii) The cyanogen variations on the giant branch appear to be accompanied by an anticorrelated variation in the abundance of the CH molecule. Spectrum synthesis analysis of a (CN strong)/(CN weak) pair of stars for which relatively high resolution data are available shows that there is a variation of ..delta..(N/A)approx.+0.9, and ..delta..(C/A)approx.-0.3, indicative of the CN cycle. (iii) On the red giant branch there are variations in the strength of the lines of Al I which correlate positively with the cyanogen variations. The size of the variations is consistent with the hypothesis that the same phenomenon has occurred in NGC 6752 and ..omega.. Centauri, but to a much smaller extent in the former. (iv) On the asymptotic giant branch (AGB), the features of CH are weaker than on the red giant branch at the same color or magnitude, and there are no examples of stars in the strong CN group. Spectrum synthesis suggests that the behavior of the CH features is consistent, on the average, with the effective temperature and gravities of the AGB stars, but that the absence of strong CN stars cannot be explained in this way. We set an upper limit of ..delta..(C/H)approx.0.3 to the possible range of carbon on the AGB at log L/L/sub sun/approx.2.3, and between this group and stars of similar color on the red giant branch. (v) Most of the stars on the anomalously low luminosity end of the AGB are not members of NGC 6752. Two stars, (CS 41 and CS 44), however, deserve further study, since they could be examples of partially mixed stars.

• Research Organization: Mount Stromlo and Siding Spring Observatories, Research School of Physical Sciences, Australian National University
• OSTI ID: 6186133
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 244:1; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640102* -- Astrophysics & Cosmology-- Stars & Quasi-Stellar
Radio & X-Ray Sources
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABUNDANCE
ALKYL RADICALS
ALUMINIUM
CHEMICAL COMPOSITION
CYANOGEN
ELEMENTS
GIANT STARS
METALS
METHYL RADICALS
PHOTOMETRY
RADICALS
SPECTROSCOPY
STAR CLUSTERS
STAR EVOLUTION
STARS