Abundance analysis of a CEMP-no star in the Carina dwarf spheroidal galaxy

Susmitha, A.; Koch, Andreas

doi:10.1051/0004-6361/201730774

Cited by 15 publications

(8 citation statements)

References 86 publications

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“…At the higher metallicities in Sculptor, [Fe/H] > −2, the rprocess seems to be well sampled, in the sense that the mean trend of [Eu/Mg] follows that of the Milky Way, and any signs Bonifacio et al 2000;McWilliam et al 2013;Fornax (violet): Shetrone et al 2003;Letarte et al 2010Letarte et al , 2018Lemasle et al 2014;Draco (pink): Shetrone et al 2001;Fulbright et al 2004;Cohen & Huang 2009; Ursa Minor (orange): Shetrone et al 2001;Sadakane et al 2004;Cohen & Huang 2010;Kirby & Cohen 2012;Carina (yellow) : Susmitha et al 2017;Norris et al 2017, which includes reanalysis of data presented in Shetrone et al (2003); Venn et al (2012); Lemasle et al (2012); ultra-faint dwarf galaxies (gray): Frebel et al 2010bFrebel et al , 2014Roederer & Kirby 2014;Ji et al 2016bJi et al ,c, 2019aHansen et al 2017. References for the Milky Way and Sculptor are listed in Fig.…”

Section: Timescales Of the R-process In The Local Groupmentioning

confidence: 97%

Neutron-capture elements in dwarf galaxies I: Chemical clocks & the short timescale of the r-process

Skúladóttir,

Hansen,

Salvadori

et al. 2019

Preprint

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The heavy elements (Z > 30) are created in neutron (n)-capture processes that are predicted to happen at vastly different nucleosynthetic sites. To study these processes in an environment different from the Milky Way, we targeted the n-capture elements in red giant branch stars in the Sculptor dwarf spheroidal galaxy. Using ESO VLT/FLAMES spectra, we measured the chemical abundances of Y, Ba, La, Nd, and Eu in 98 stars covering the metalliticy range −2.4 < [Fe/H] < −0.9. This is the first paper in a series about the n-capture elements in dwarf galaxies, and here we focus on the relative and absolute timescales of the slow (s)-and rapid (r)-processes in Sculptor. From the abundances of the s-process element Ba and the r-process element Eu, it is clear that the r-process enrichment occurred throughout the entire chemical evolution history of Sculptor. Furthermore, there is no evidence for the r-process to be significantly delayed in time relative to core-collapse supernovae. Neutron star mergers are therefore unlikely the dominant (or only) nucleosynthetic site of the r-process. However, the products of the s-process only become apparent at [Fe/H] ≈ −2 in Sculptor, and the s-process becomes the dominant source of Ba at [Fe/H] −2. We tested the use of [Y/Mg] and [Ba/Mg] as chemical clocks in Sculptor. Similarly to what is observed in the Milky Way, [Y/Mg] and [Ba/Mg] increase towards younger ages. However, there is an offset in the trends, where the abundance ratios of [Y/Mg] in Sculptor are significantly lower than those of the Milky Way at any given age. This is most likely caused by metallicity dependence of yields from the s-process, as well as by a different relative contribution of the s-process to core-collapse supernovae in these galaxies. Comparisons of our results with data of the Milky Way and the Fornax dwarf spheroidal galaxy furthermore show that these chemical clocks depend on both metallicity and environment.

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Section: Timescales Of the R-process In The Local Groupmentioning

confidence: 97%

Neutron-capture elements in dwarf galaxies I: Chemical clocks & the short timescale of the r-process

Skúladóttir,

Hansen,

Salvadori

et al. 2019

Preprint

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“…The fraction of CEMP stars in the halo and in metal-poor dwarf spheroidal galaxies is known to significantly increase with decreasing metallicity (e.g., Norris et al 2010;Carollo et al 2012;Salvadori et al 2015;Skúladóttir et al 2015;Hansen et al 2015bHansen et al , 2016aSusmitha et al 2017) and also the bulge's metalpoor population can be expected to follow this trend (Tumlinson 2007(Tumlinson , 2010. It is then interesting to note that the bulge CH-star falls right on the peak of the halo MDF, and the CEMP-s lies at the peak of the halo CEMP star distribution.…”

Section: Carbon-rich Bulge Starsmentioning

confidence: 99%

Unusual neutron-capture nucleosynthesis in a carbon-rich Galactic bulge star

Koch

Reichert

Hansen

et al. 2019

A&A

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Metal-poor stars in the Galactic halo often show strong enhancements in carbon and/or neutron-capture elements. However, the Galactic bulge is notable for its paucity of these carbon-enhanced metal-poor (CEMP) and/or CH-stars, with only two such objects known to date. This begs the question whether the processes that produced their abundance distribution were governed by a comparable nucleosynthesis in similar stellar sites as for their more numerous counterparts in the halo. Recently, two contenders of these classes of stars were discovered in the bulge, at [Fe/H] = −1.5 and −2.5 dex, both of which show enhancements in [C/Fe] of 0.4 and 1.4 dex (respectively), [Ba/Fe] in excess of 1.3 dex, and also elevated nitrogen. The more metal-poor of the stars can be well matched by standard s-process nucleosynthesis in low-mass Asymptotic Giant Branch (AGB) polluters. The other star shows an abnormally high [Rb/Fe] ratio. Here, we further investigate the origin of the abundance peculiarities in the Rb-rich star by new, detailed measurements of heavy element abundances and by comparing the chemical element ratios of 36 species to several models of neutron-capture nucleosynthesis. The i-process with intermediate neutron densities between those of the slow (s-) and rapid (r)-neutron-capture processes has been previously found to provide good matches of CEMP stars with enhancements in both r-and s-process elements (class CEMP-r/s), rather than invoking a superposition of yields from the respective individual processes. However, the peculiar bulge star is incompatible with a pure i-process from a single ingestion event. Instead, it can, statistically, be better reproduced by more convoluted models accounting for two proton ingestion events, or by an i-process component in combination with s-process nucleosynthesis in low-to-intermediate mass (2-3 M ) AGB stars, indicating multiple polluters. Finally, we discuss the impact of mixing during stellar evolution on the observed abundance peculiarities.

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“…The CEMP-no stars in dwarf galaxies are not extensively studied (e.g., Salvadori et al 2015). However, three CEMP-no stars in dwarf galaxies are of special interest: ET0097 1 in Sculptor (Skúladóttir et al 2015a), ALW-8 in Carina (Susmitha et al 2017), and 10694 in Pisces II (Spite et al 2018). These three stars all show enhancements of [Sr, Y, Zr/Ba] > +0.7, which is not typical for CEMP-no stars in the Milky Way (e.g., Allen et al 2012, and references therein).…”

Section: Introductionmentioning

confidence: 99%

Neutron-capture elements in dwarf galaxies

Skúladóttir

Hansen

Choplin

et al. 2020

A&A

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The slow (s) and intermediate (i) neutron (n) capture processes occur both in asymptotic giant branch (AGB) stars, and in massive stars. To study the build-up of the s- and i-products at low metallicity, we investigate the abundances of Y, Ba, La, Nd, and Eu in 98 stars, at −2.4 < [Fe/H] < −0.9, in the Sculptor dwarf spheroidal galaxy. The chemical enrichment from AGB stars becomes apparent at [Fe/H] ≈ −2 in Sculptor, and causes [Y/Ba], [La/Ba], [Nd/Ba] and [Eu/Ba] to decrease with metallicity, reaching subsolar values at the highest [Fe/H] ≈ −1. To investigate individual nucleosynthetic sites, we compared three n-rich Sculptor stars with theoretical yields. One carbon-enhanced metal-poor (CEMP-no) star with high [Sr, Y, Zr] > +0.7 is best fit with a model of a rapidly-rotating massive star, the second (likely CH star) with the i-process, while the third has no satisfactory fit. For a more general understanding of the build-up of the heavy elements, we calculate for the first time the cumulative contribution of the s- and i-processes to the chemical enrichment in Sculptor, and compare with theoretical predictions. By correcting for the r-process, we derive [Y/Ba]s/i = −0.85 ± 0.16, [La/Ba]s/i = −0.49 ± 0.17, and [Nd/Ba]s/i = −0.48 ± 0.12, in the overall s- and/or i-process in Sculptor. These abundance ratios are within the range of those of CEMP stars in the Milky Way, which have either s- or i-process signatures. The low [Y/Ba]s/i and [La/Ba]s/i that we measure in Sculptor are inconsistent with them arising from the s-process only, but are more compatible with models of the i-process. Thus we conclude that both the s- and i-processes were important for the build-up of n-capture elements in the Sculptor dwarf spheroidal galaxy.

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Abundance analysis of a CEMP-no star in the Carina dwarf spheroidal galaxy

Cited by 15 publications

References 86 publications

Neutron-capture elements in dwarf galaxies I: Chemical clocks & the short timescale of the r-process

Neutron-capture elements in dwarf galaxies I: Chemical clocks & the short timescale of the r-process

Unusual neutron-capture nucleosynthesis in a carbon-rich Galactic bulge star

Neutron-capture elements in dwarf galaxies

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