Neutron-capture elements in dwarf galaxies

Skúladóttir, Ása; Hansen, C. J.; Choplin, Arthur; Salvadori, Stefania; Hampel, Melanie; Campbell, Simon

doi:10.1051/0004-6361/201937075

Cited by 26 publications

(34 citation statements)

References 144 publications

(276 reference statements)

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“…We note, however, that for tidally disrupted galaxies, this may not be a good substitute (e.g., Tolstoy et al 2009;McConnachie 2012). Nevertheless, a large deviation from the mass and luminosity relation should only apply for a strong tidal disruption, because the galaxies dark matter is thought to get disrupted before the stars and the impact on the luminosity may therefore be minor (see e.g., Smith et al 2016). More massive systems are expected to keep or synthesize their metals more efficiently, leading in most cases to the appearance of the α-knee at higher metallicities due to an extended SFH.…”

Section: The Imf and The Alpha Kneementioning

confidence: 96%

Neutron-capture elements in dwarf galaxies

Reichert

Hansen

Hanke

et al. 2020

A&A

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Context. We present a large homogeneous set of stellar parameters and abundances across a broad range of metallicities, involving 13 classical dwarf spheroidal (dSph) and ultra-faint dSph (UFD) galaxies. In total, this study includes 380 stars in Fornax, Sagittarius, Sculptor, Sextans, Carina, Ursa Minor, Draco, Reticulum II, Bootes I, Ursa Major II, Leo I, Segue I, and Triangulum II. This sample represents the largest, homogeneous, high-resolution study of dSph galaxies to date. Aims. With our homogeneously derived catalog, we are able to search for similar and deviating trends across different galaxies. We investigate the mass dependence of the individual systems on the production of α-elements, but also try to shed light on the long-standing puzzle of the dominant production site of r-process elements. Methods. We used data from the Keck observatory archive and the ESO reduced archive to reanalyze stars from these 13 classical dSph and UFD galaxies. We automatized the step of obtaining stellar parameters, but ran a full spectrum synthesis (1D, local thermal equilibrium) to derive all abundances except for iron to which we applied nonlocal thermodynamic equilibrium corrections where possible. Results. The homogenized set of abundances yielded the unique possibility of deriving a relation between the onset of type Ia supernovae and the stellar mass of the galaxy. Furthermore, we derived a formula to estimate the evolution of α-elements. This reveals a universal relation of these systems across a large range in mass. Finally, we show that between stellar masses of 2.1 × 107 M⊙ and 2.9 × 105 M⊙, there is no dependence of the production of heavy r-process elements on the stellar mass of the galaxy. Conclusions. Placing all abundances consistently on the same scale is crucial to answering questions about the chemical history of galaxies. By homogeneously analyzing Ba and Eu in the 13 systems, we have traced the onset of the s-process and found it to increase with metallicity as a function of the galaxy’s stellar mass. Moreover, the r-process material correlates with the α-elements indicating some coproduction of these, which in turn would point toward rare core-collapse supernovae rather than binary neutron star mergers as a host for the r-process at low [Fe/H] in the investigated dSph systems.

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Section: The Imf and The Alpha Kneementioning

confidence: 96%

Neutron-capture elements in dwarf galaxies

Reichert

Hansen

Hanke

et al. 2020

A&A

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“…Barium is a heavy element that is mainly produced in AGB stars, via the slow neutron capture process (Karakas & Lattanzio 2014), and possibly also the intermediate neutron capture process (Hampel et al 2016(Hampel et al , 2019Skúladóttir et al 2020). In Fig.…”

Section: Bariummentioning

confidence: 99%

The GALAH Survey: non-LTE departure coefficients for large spectroscopic surveys

Amarsi

Lind

Osorio

et al. 2020

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Massive sets of stellar spectroscopic observations are rapidly becoming available and these can be used to determine the chemical composition and evolution of the Galaxy with unprecedented precision. One of the major challenges in this endeavour involves constructing realistic models of stellar spectra with which to reliably determine stellar abundances. At present, large stellar surveys commonly use simplified models that assume that the stellar atmospheres are approximately in local thermodynamic equilibrium (LTE). To test and ultimately relax this assumption, we have performed non-LTE calculations for 13 different elements (H, Li, C, N, O, Na, Mg, Al, Si, K, Ca, Mn, and Ba), using recent model atoms that have physically-motivated descriptions for the inelastic collisions with neutral hydrogen, across a grid of 3756 1D MARCS model atmospheres that spans 3000 ≤ Teff∕K ≤ 8000, − 0.5 ≤log g∕cm s−2 ≤ 5.5, and − 5 ≤ [Fe/H] ≤ 1. We present the grids of departure coefficients that have been implemented into the GALAH DR3 analysis pipeline in order to complement the extant non-LTE grid for iron. We also present a detailed line-by-line re-analysis of 50 126 stars from GALAH DR3. We found that relaxing LTE can change the abundances by between − 0.7 dex and + 0.2 dex for different lines and stars. Taking departures from LTE into account can reduce the dispersion in the [A/Fe] versus [Fe/H] plane by up to 0.1 dex, and it can remove spurious differences between the dwarfs and giants by up to 0.2 dex. The resulting abundance slopes can thus be qualitatively different in non-LTE, possibly with important implications for the chemical evolution of our Galaxy. The grids of departure coefficients are publicly available and can be implemented into LTE pipelines to make the most of observational data sets from large spectroscopic surveys.

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“…Their heavy-element abundances would classify them as CEMP-r/s according to the Beers & Christlieb (2005) scheme, but their carbon abundance has never been determined. Sculptor 982 is reported (Hill et al 2019;Skúladóttir et al 2020) to show very strong CN bands, a further hint in this direction.…”

Section: Discussionmentioning

confidence: 94%

A wide angle view of the Sagittarius dwarf spheroidal galaxy

Sbordone

Hansen

Monaco

et al. 2020

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We report on the discovery and chemical abundance analysis of the first CEMP-r/s star detected in the Sagittarius dwarf spheroidal galaxy (Sgr dSph) by means of UVES high-resolution spectra. The star, found in the outskirts of Sgr dSph, along the major axis of the main body, is a moderately metal-poor giant (Teff = 4753 K, log g = 1.75, [Fe/H] = −1.55) with [C/Fe] = 1.13, placing it in the so-called “high-carbon band”, and strong s-process and r-process enrichment ([Ba/Fe] = 1.4, [Eu/Fe] = 1.01). Abundances of 29 elements from C to Dy were obtained. The chemical pattern appears to be best fitted by a scenario where an r-process pollution event pre-enriched the material out of which the star was born as secondary in a binary system whose primary evolved through the AGB phase, providing C- and s-process enrichment.

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Neutron-capture elements in dwarf galaxies

Cited by 26 publications

References 144 publications

Neutron-capture elements in dwarf galaxies

Neutron-capture elements in dwarf galaxies

The GALAH Survey: non-LTE departure coefficients for large spectroscopic surveys

A wide angle view of the Sagittarius dwarf spheroidal galaxy

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