Nitrogen abundances in giant stars of the globular cluster NGC 6752

TL;DR

This study measures nitrogen abundances in 21 giant stars of NGC 6752, confirming the correlation with the Stromgren c1 index and suggesting multiple stellar sources for observed abundance variations.

Contribution

First detailed nitrogen abundance analysis in NGC 6752 giants using high-resolution spectra, revealing correlations with other elements and implications for stellar nucleosynthesis sources.

Findings

Star-to-star N variation is 1.95 dex.

Correlations between N and other elements are statistically significant.

Heavy element variations, if real, imply synthesis in stars producing multiple element groups.

Abstract

We present N abundances for 21 bright giants in the globular cluster NGC 6752 based on high-resolution UVES spectra of the 3360A NH lines. We confirm that the Stromgren c1 index traces the N abundance and find that the star-to-star N abundance variation is 1.95 dex, at the sample's luminosity. We find statistically significant correlations, but small amplitude variations, between the abundances of N and alpha-, Fe-peak, and s-process elements. Analyses using model atmospheres with appropriate N, O, Na, and Al abundances would strengthen, rather than mute, these correlations. If the small variations of heavy elements are real, then the synthesis of the N anomalies must take place in stars which also synthesize alpha-, Fe-peak, and s-process elements. These correlations offer support for contributions from both AGB and massive stars to the globular cluster abundance anomalies.