Detailed analysis of a sample of field metal-poor N-rich dwarfs

TL;DR

This study compares the chemical compositions of metal-poor N-rich dwarf stars with globular cluster stars, providing evidence that these field stars likely originated as second-generation stars within GCs.

Contribution

It offers the first detailed chemical analysis linking field N-rich dwarfs to second-generation globular cluster stars, including establishing the Na-O anti-correlation in field stars.

Findings

N-rich stars show C and O deficiency with small [(C+N+O)/Fe] scatter.

N-rich stars exhibit Na and Al excess similar to GC second-generation stars.

Na-O anti-correlation observed in field N-rich stars, supporting their GC origin.

Abstract

Aims. The aim of this work is to compare the detailed chemical composition of the field N-rich dwarf stars to the second generation stars of globular clusters (GC) in order to investigate the hypothesis that they originated in GCs. Methods. We have measured the abundance of 23 elements (from Li to Eu) in a sample of six metal-poor N-rich stars (three of them pointed out for the first time) and we have compared their chemical composition to, (i) the chemical composition observed in a sample of classical metal-poor stars, and (ii) the abundances observed in the second generation stars of GCs. Results. In metal-poor N-rich stars C and O are slightly deficient but the scatter of [(C+N+O)/Fe] is very small, a strong indication that the N enrichment is the result of a pollution by CNO processed material. The N-rich stars of our sample, like the second generation stars in the GCs, show an excess of Na and sometimes of Al, as expected if the material from which these stars were formed, has been polluted by the ejecta of massive AGB stars. For the first time we have been able to establish an anti-correlation Na-O in field stars like the one observed in NGC6752. The N-rich star HD 74000 has a rather low [Eu/Ba] ratio for its metallicity. Such an anomaly is also observed in several second generation stars of M15. Conclusions. This analysis supports the hypothesis that the N-rich stars today observed in the field, were born as second generation stars in GCs.