Homogeneity in the early chemical evolution of the Sextans dwarf Spheroidal galaxy

Abstract

We present the high-resolution spectroscopic analysis of two new extremely metal-poor stars (EMPS) candidates in the dwarf spheroidal galaxy Sextans. These targets were pre-selected from medium resolution spectra centered around the Ca ii triplet in the near-infrared and followed-up at higher resolution with VLT/UVES. We confirm their low metallicities with [Fe/H]=−2.95 and [Fe/H]=−3.01, placing them among the most metal-poor stars known in Sextans. The abundances of 18 elements, including C, Na, the α, Fe-peak, and neutron capture elements, are determined. In particular, we present the first measurements of Zn in a classical dwarf at extremely low metallicity. There has been previous hints of a large scatter in the abundance ratios of the Sextans stellar population around [Fe/H]∼ −3 when compared to other galaxies. We took the opportunity of this work to re-analyse the full sample of EMPS and find a Milky-Way -like plateau and a normal dispersion at fixed metallicity.

The Pristine survey -- XII: Gemini-GRACES chemo-dynamical study of newly discovered extremely metal-poor stars in the Galaxy

“…Alternatively, Gaia-Sequoia may have had episodes of star formation that stochastically enriched its interstellar medium, providing a range in some elements, like Mg. Similar abundance patterns have been seen in EMP stars in dwarf galaxies, such as Carina and Sextans (Norris et al 2017;de Boer et al 2014;Theler et al 2020;Lucchesi et al 2020). Furthermore, two of our Gaia-Sequoia candidates (P021+32 and P133+28) may be enriched in potassium (see Figs.…”

“…In dwarf galaxies, the abundance ratios of hydrostatic elements (𝑒.𝑔., O, Na, Mg), explosive elements (𝑒.𝑔., Si, K, Mn), complex elements (like Zn), and heavy elements (as Ba, Y) tend to be lower than those of their Galactic counterparts of similar metallicity. This reflects a range of differences in their star formation histories, including interstellar mixing efficiencies, star formation efficiencies, star formation rates, and effective mass functions of the dwarf galaxy systems (Venn et al 2004;Tolstoy et al 2009;Nissen & Schuster 2010;McWilliam et al 2013;Frebel & Norris 2015;Hasselquist et al 2017;Hayes et al 2018;Lucchesi et al 2020). The diversity of chemical abundance profiles seen in this sparse population of 1 We adopt the square bracket notation for chemical abundances relative to the Sun, such that [X/Y] = log(X/Y) − log(X/Y) * , where X and Y are column densities for two given elements.…”

Forecasting Chemical Abundance Precision for Extragalactic Stellar Archaeology

“…FLAMES-UVES is a high resolution spectrograph with a more limited wavelength coverage (only 4800-6800 Å), but is capable of observing up to 8 stars at a time thanks to the FLAMES fiber feed 26 . It has been used to observe RGB stars in MW globular clusters (e.g., Alves-Brito et al 2006) and in nearby dwarf galaxies (e.g., Shetrone et al 2003;Letarte et al 2006;Hill et al 2019;Lucchesi et al 2020). X-SHOOTER has also been used to measure abundances of bright stars in dwarf galaxies (Starkenburg et al 2013;Spite et al 2018) and provides slightly lower resolution than MIKE, HIRES, and UVES but significantly higher throughput and broader wavelength coverage 27 .…”

Neutron-capture elements in dwarf galaxies III: A homogenized analysis of 13 dwarf spheroidal and ultra-faint galaxies

“…3.6 of Theler 2015 andTheler et al 2019). For more information of the two of our most metalpoor stars in Sextans, we refer the reader to Lucchesi et al 2020). In order to test 11 whether a model with two knees should be favored over a model with one, we apply the Akaike information criterion (AIC, Akaike 1974) and the Bayesian information criterion (BIC, Schwarz 1978).…”