Detection of a Population of Carbon-enhanced Metal-poor Stars in the Sculptor Dwarf Spheroidal Galaxy<sup>∗</sup>

Chiti, Anirudh; Simon, Joshua D.; Frebel, Anna; Thompson, I. B.; Shectman, Stephen; Mateo, Mario; Bailey, John I.; Crane, Jeffrey D.; Walker, Matthew G.

doi:10.3847/1538-4357/aab663

Cited by 36 publications

(28 citation statements)

References 107 publications

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“…Figure 8 shows that the carbon-enhanced fraction in UFDs is essentially identical to halo stars at all levels of carbon enhancement. For comparison, the CEMP fraction in larger dwarf galaxies like Sculptor has been studied in some detail (e.g., Skúladóttir et al 2015;Salvadori et al 2015;Chiti et al 2018b), but it is still debated whether the CEMP fraction in those galaxies is consistent with the halo.…”

Section: Carbon-enhanced Fraction In Ufdsmentioning

confidence: 99%

Detailed Abundances in the Ultra-faint Magellanic Satellites Carina II and III

Simon

et al. 2020

ApJ

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We present the first detailed elemental abundances in the ultra-faint Magellanic satellite galaxies Carina II (Car II) and Carina III (Car III). With high-resolution Magellan/MIKE spectroscopy, we determined abundances of nine stars in Car II including the first abundances of an RR Lyrae star in an ultra-faint dwarf galaxy; and two stars in Car III. The chemical abundances demonstrate that both systems are clearly galaxies and not globular clusters. The stars in these galaxies mostly display abundance trends matching those of other similarly faint dwarf galaxies: enhanced but declining [α/Fe] ratios, iron-peak elements matching the stellar halo, and unusually low neutron-capture element abundances. One star displays a low outlying [Sc/Fe]= −1.0. We detect a large Ba scatter in Car II, likely due to inhomogeneous enrichment by low-mass AGB star winds. The most striking abundance trend is for [Mg/Ca] in Car II, which decreases from +0.4 to −0.4 and indicates clear variation in the initial progenitor masses of enriching core-collapse supernovae. So far, the only ultra-faint dwarf galaxies displaying a similar [Mg/Ca] trend are likely satellites of the Large Magellanic Cloud. We find two stars with [Fe/H] ≤ −3.5, whose abundances likely trace the first generation of metal-free Population III stars and are well-fit by Population III core-collapse supernova yields. An appendix describes our new abundance uncertainty analysis that propagates line-by-line stellar parameter uncertainties.

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Section: Carbon-enhanced Fraction In Ufdsmentioning

confidence: 99%

Detailed Abundances in the Ultra-faint Magellanic Satellites Carina II and III

Simon

et al. 2020

ApJ

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“…1. The low-metallicity tail of the galaxy, [Fe/H] < −2.5, is not included in our sample, but has been studied elsewhere (Tafelmeyer et al 2010;Frebel et al 2010a;Starkenburg et al 2013;Jablonka et al 2015;Simon et al 2015;Chiti et al 2018). Similarly, our target sample is biased toward younger stars because they mainly reside in the center of the galaxy (Tolstoy et al 2004;de Boer et al 2012a).…”

Section: Target Samplementioning

confidence: 99%

Neutron-capture elements in dwarf galaxies

Skúladóttir

Hansen

Salvadori

et al. 2019

A&A

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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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“…However, CEMP stars are not found in all environments. For instance, only a few s-process rich CEMP stars have been detected in the direction of the Milky Way bulge (Howes et al 2015;Koch et al 2016) and studies generally tend to find a lower fraction of CEMP stars in dSphs (Kirby et al 2015;Jablonka et al 2015;Chiti et al 2018), but a small number have been detected in the ultrafaint dwarf galaxies (Frebel & Norris 2015).…”

Section: The Signature Of Carbon In the Sagittarius Dsphmentioning

confidence: 99%

Four Metal-poor Stars in the Sagittarius Dwarf Spheroidal Galaxy^∗

Chiti

Frebel

2019

ApJ

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We present the metallicities and carbon abundances of four newly discovered metal-poor stars with −2.2 < [Fe/H] < −1.6 in the Sagittarius dwarf spheroidal galaxy. These stars were selected as metalpoor member candidates using a combination of public photometry from the SkyMapper Southern Sky Survey and proper motion data from the second data release from the Gaia mission. The SkyMapper filters include a metallicity-sensitive narrow-band v filter centered on the Ca II K line, which we use to identify metal-poor candidates. In tandem, we use proper motion data to remove metal-poor stars that are not velocity members of the Sagittarius dwarf spheroidal galaxy. We find that these two datasets allow for efficient identification of metal-poor members of the Sagittarius dwarf galaxy to follow-up with further spectroscopic study. Two of the stars we present have [Fe/H] < −2.0, which adds to the few other such stars currently identified in the Sagittarius dwarf galaxy that are likely not associated with the globular cluster M54, which resides in the nucleus of the system. Our results confirm that there exists a very metal-poor stellar population in the Sagittarius dwarf galaxy. We find that none of our stars can be classified as carbon-enhanced metal-poor stars. Efficiently identifying members of this population will be helpful to further our understanding of the early chemical evolution of the system.

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Detection of a Population of Carbon-enhanced Metal-poor Stars in the Sculptor Dwarf Spheroidal Galaxy^∗

Cited by 36 publications

References 107 publications

Detailed Abundances in the Ultra-faint Magellanic Satellites Carina II and III

Detailed Abundances in the Ultra-faint Magellanic Satellites Carina II and III

Neutron-capture elements in dwarf galaxies

Four Metal-poor Stars in the Sagittarius Dwarf Spheroidal Galaxy^∗

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Detection of a Population of Carbon-enhanced Metal-poor Stars in the Sculptor Dwarf Spheroidal Galaxy∗

Cited by 36 publications

References 107 publications

Detailed Abundances in the Ultra-faint Magellanic Satellites Carina II and III

Detailed Abundances in the Ultra-faint Magellanic Satellites Carina II and III

Neutron-capture elements in dwarf galaxies

Four Metal-poor Stars in the Sagittarius Dwarf Spheroidal Galaxy∗

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Product

Resources

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Detection of a Population of Carbon-enhanced Metal-poor Stars in the Sculptor Dwarf Spheroidal Galaxy^∗

Four Metal-poor Stars in the Sagittarius Dwarf Spheroidal Galaxy^∗