Learning about the Intermediate Neutron-capture Process from Lead Abundances*

Hampel, Melanie; Karakas, Amanda I.; Stancliffe, Richard J.; Meyer, B. S.; Lugaro, Maria

doi:10.3847/1538-4357/ab4fe8

Cited by 51 publications

(66 citation statements)

References 110 publications

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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

A&A

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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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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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“…The range of the pure i-process at Z = 10 −4 is in green, where light green refers to n-densities of 10 12 ≤ n d /cm −3 ≤ 10 14 , and dark green assumes higher 10 14 < n d /cm −3 ≤ 10 15 (Hampel et al 2016). CEMP-s references: Aoki et al (2002), Cohen et al (2013), Roederer et al (2014); CEMP-i references: Aoki et al (2002), Goswami et al (2006), Behara et al (2010), Cohen et al (2013), Cui et al (2013), Hansen et al (2015), Hampel et al (2019) (which includes the sample from Abate et al 2015b).…”

Section: Correcting For the R-processmentioning

confidence: 99%

“…Its abundance pattern overlaps with that of the s-process, but overall it is different from both the s-or r-processes, or a mixture of the products of the two (e.g., Fishlock et al 2014;Hampel et al 2016;Roederer et al 2016). The nucleosynthetic sites of the i-process remain unconfirmed (e.g., Frebel 2018;Koch et al 2019), but among the proposed scenarios are: low-mass, lowmetallicity ([Fe/H] −3) stars (Campbell & Lattanzio 2008;Campbell et al 2010;Cruz et al 2013;Cristallo et al 2016), massive (5−10 M ) super-AGB stars (Doherty et al 2015;Jones et al 2016), evolved low-mass stars (Herwig et al 2011;Hampel et al 2019), and rapidly accreting white dwarfs (Herwig et al 2014;Denissenkov et al 2017). Finally, massive (m > 20 M ), metalpoor stars could also play a role in the production of i-process elements (Clarkson et al 2018;Banerjee et al 2018).…”

Section: Introductionmentioning

confidence: 99%

Neutron-capture elements in dwarf galaxies

Skúladóttir

Hansen

Choplin

et al. 2020

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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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“…Heavy elements (with atomic numbers Z > 30) are dominantly produced in the slow (s) and rapid (r) neutron-capture process. The intermediate (i) process (e.g., Dardelet et al 2015;Hampel et al 2016Hampel et al , 2019Banerjee et al 2018;Koch et al 2019; and the light element primary process (LEPP, e.g., Travaglio et al 2004;Montes et al 2007) may also contribute to the enrichment of heavy elements. Both the s-and the r-process are hosted by distinct astrophysical production sites and carry individual chemical fingerprints (for reviews of the r-process and the origin of heavy elements see, e.g., Cowan et al 1991Cowan et al , 2019Sneden et al 2008;Thielemann et al 2011Thielemann et al , 2017Frebel 2018;Horowitz et al 2019).…”

Section: Introductionmentioning

confidence: 99%

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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Learning about the Intermediate Neutron-capture Process from Lead Abundances*

Cited by 51 publications

References 110 publications

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

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

Neutron-capture elements in dwarf galaxies

Neutron-capture elements in dwarf galaxies

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