An investigation of C, N, and Na abundances in red giant stars of the Sculptor dwarf spheroidal galaxy

Abstract

The origin of the star-to-star abundance variations found for the light elements in Galactic globular clusters (GGCs) is not well understood, which is a significant problem for stellar astrophysics. While the light element abundance variations are very common in globular clusters, they are comparatively rare in the Galactic halo field population. However, little is known regarding the occurrence of the abundance anomalies in other environments such as that of dwarf spheroidal (dSph) galaxies. Consequently, we have investigated the anti-correlation and bimodality of CH and CN band strengths, which are markers of the abundance variations in GGCs, in the spectra of red giants in the Sculptor dwarf spheroidal galaxy. Using spectra at the Na D lines, informed by similar spectra for five GGCs (NGC 288, 1851, 6752, 6809 and 7099), we have also searched for any correlation between CN and Na in the Sculptor red giant sample. Our results indicate that variations analogous to those seen in GGCs are not present in our Sculptor sample. Instead, we find a weak positive correlation between CH and CN, and no correlation between Na and CN. We also reveal a deficiency in [Na/Fe] for the Sculptor stars relative to the values in GGCs, a result which is consistent with previous work for dSph galaxies. The outcomes reinforce the apparent need for a high stellar density environment to produce the light element abundance variations.

Purveyors of fine halos

“…Here, the blue and red histograms represent the findings from methods I and III, respectively. For comparison, we indicate the fractions for bound cluster stars as reported by Carretta et al (2009, solid dence for CN-bimodalities amongst the dSph field star populations is sparse (e.g., Smith & Dopita 1983;Lardo et al 2016a;Norris et al 2017;Salgado et al 2019). However, several GCs in the MW have been associated with dwarf-accretion events.…”

“…As a consequence, the number of chemically normal stars that are erroneously classified as 1P stars would be artificially increased, which in turn would lead to a higher N 1P /N tot . Evi- dence for CN-bimodalities amongst the dSph field star populations is sparse (e.g., Smith & Dopita 1983;Lardo et al 2016a;Norris et al 2017;Salgado et al 2019). However, several GCs in the MW have been associated with dwarf-accretion events.…”

Different Sodium enhancements among multiple populations of Milky Way globular clusters

“…It has been shown that the most Na-poor limit in dwarf galaxies is lower than the Na abundance of Milky Way field stars, with some exceptions (Colucci et al 2012;Ishigaki et al 2014;Battaglia et al 2017;Villanova et al 2019;Salgado et al 2019;Matsuno et al 2019;Aguado et al 2020). Therefore, first generation stars of globular clusters formed in accreted dwarf galaxies should mostly have Na abundances lower than their counterparts of globular clusters formed in situ, which explains the range of 1G values seen in Figure 1.…”

Different sodium enhancements among multiple populations of Milky Way globular clusters

“…It has been shown that the most Na-poor limit in dwarf galaxies is lower than the Na abundance of Milky Way field stars, with some exceptions (Colucci et al 2012;Ishigaki et al 2014;Battaglia et al 2017;Villanova et al 2019;Salgado et al 2019;Matsuno et al 2019;Aguado et al 2020). Therefore, first generation stars of globular clusters formed in accreted dwarf galaxies should mostly have Na abundances lower than their counterparts of globular clusters that formed in situ, which explains the range of 1G values seen in Fig.…”