scholarly journals α-Process Elements in the Galaxy: A Possible GAIA Contribution

2002 ◽  
pp. 143-150
Author(s):  
Gražina Tautvaišienė ◽  
Bengt Edvardsson
Keyword(s):  
The Galaxy ◽  
Process Elements

scholarly journals R-process enrichment in ultrafaint dwarf galaxies

2020 ◽  
Vol 494 (1) ◽  
pp. 120-128 ◽  
Author(s):  
Yuta Tarumi ◽  
Naoki Yoshida ◽  
Shigeki Inoue
Keyword(s):  
Star Formation ◽  
Neutron Star ◽  
Galaxy Formation ◽  
Dwarf Galaxies ◽  
Long Distance ◽  
Stellar Feedback ◽  
The Galaxy ◽  
Star Binary ◽  
R Process ◽  
Process Elements

ABSTRACT We study the enrichment and mixing of r-process elements in ultrafaint dwarf galaxies (UFDs). We assume that r-process elements are produced by neutron-star mergers (NSMs), and examine multiple models with different natal kick velocities and explosion energies. To this end, we perform cosmological simulations of galaxy formation to follow mixing of the dispersed r-process elements driven by star formation and the associated stellar feedback in progenitors of UFDs. We show that the observed europium abundance in Reticulum II is reproduced by our inner explosion model where an NSM is triggered at the centre of the galaxy, whereas the relatively low abundance in Tucana III is reproduced if an NSM occurs near the virial radius of the progenitor galaxy. The latter case is realized only if the neutron-star binary has a large natal kick velocity and travels over a long distance of a kiloparsec before merger. In both the inner and outer explosion cases, it is necessary for the progenitor galaxy to sustain prolonged star formation over a few hundred million years after the NSM, so that the dispersed r-process elements are well mixed within the interstellar medium. Short-duration star formation results in inefficient mixing, and then a large variation is imprinted in the stellar europium abundances, which is inconsistent with the observations of Reticulum II and Tucana III.

scholarly journals The Missing Lead: Developments in the Lead (Pb) Discrepancy in Intrinsically s-Process Enriched Single Post-AGB Stars

Universe ◽  
2021 ◽  
Vol 7 (11) ◽  
pp. 446
Author(s):  
Devika Kamath ◽  
Hans Van Winckel
Keyword(s):  
Magellanic Clouds ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Chemical Abundance ◽  
Major Development ◽  
Upper Limits ◽  
The Galaxy ◽  
Process Elements ◽  
Detailed Chemical ◽  
Theoretical Developments

Lead (Pb) is predicted to have large over-abundances with respect to other s-process elements in Asymptotic Giant Branch (AGB) stars, especially of low metallicities. However, our previous abundance studies of s-process enriched post-Asymptotic Giant Branch (post-AGB) stars in the Galaxy and the Magellanic Clouds show a discrepancy between observed and predicted Pb abundances. For the subset of post-AGB stars with low metallicities the determined upper limits based on detailed chemical abundance studies are much lower than what is predicted. Recent theoretical studies have pointed to the occurrence of the i-process to explain the observed chemical patterns, especially of Pb. A major development, in the observational context, is the release of the GAIA EDR3 parallaxes of the post-AGBs in the Galaxy, which has opened the gateway to systematically studying the sample of stars as a function of current luminosities (which can be linked to their initial masses). In this paper, we succinctly review the Pb discrepancy in post-AGB stars and present the latest observational and theoretical developments in this research landscape.

scholarly journals The Yields of r-Process Elements and Chemical Evolution of the Galaxy

2006 ◽  
Vol 306 (1-2) ◽  
pp. 33-39 ◽  
Author(s):  
Zhe Chen ◽  
Jiang Zhang ◽  
YanPing Chen ◽  
WenYuan Cui ◽  
Bo Zhang
Keyword(s):  
Chemical Evolution ◽  
The Galaxy ◽  
R Process ◽  
Process Elements

The role of asymptotic giant branch stars in the chemical evolution of the Galaxy

2018 ◽  
Vol 14 (S343) ◽  
pp. 510-511
Author(s):  
G. Tautvaišienė ◽  
C. Viscasillas Vázquez ◽  
V. Bagdonas ◽  
R. Smiljanic ◽  
A. Drazdauskas ◽  
...  
Keyword(s):  
High Resolution ◽  
Neutron Capture ◽  
Open Clusters ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Galactic Disc ◽  
The Galaxy ◽  
Process Elements ◽  
Giant Branch Stars

AbstractAsymptotic giant branch stars play an important role in enriching galaxies by s-process elements. Recent studies have shown that their role in producing s-process elements in the Galactic disc was underestimated and should be reconsidered. Based on high-resolution spectra we have determined abundances of neutron-capture elements in a sample of 310 stars located in the field and open clusters and investigated elemental enrichment patterns according to their age and mean galactocentric distances.

scholarly journals Abundances of α-Process Elements in Thin-Disk, Thick-Disk, and Halo Stars of the Galaxy: Non-LTE Analysis

2019 ◽  
Vol 63 (9) ◽  
pp. 726-738 ◽  
Author(s):  
L. I. Mashonkina ◽  
M. D. Neretina ◽  
T. M. Sitnova ◽  
Yu. V. Pakhomov
Keyword(s):  
Thin Disk ◽  
Thick Disk ◽  
Halo Stars ◽  
The Galaxy ◽  
Process Elements

scholarly journals TYC5594-576-1: R-PROCESS ENRICHMENT METAL-POOR STAR

2021 ◽  
Vol 34 ◽  
pp. 48-52
Author(s):  
T.V. Mishenina ◽  
I.A. Usenko ◽  
A.Yu. Kniazev ◽  
V. V. Kovtyukh
Keyword(s):  
Synthetic Spectrum ◽  
Carbon Abundance ◽  
The Galaxy ◽  
The Status ◽  
Molecular Synthesis ◽  
R Process ◽  
Process Elements ◽  
Early Galaxy ◽  
First Time ◽  
Poor Population

Atmospheric parameters and elemental abundances of metal-poor Population II star  TYC5594-576-1 ([Fe/H] = –2.8) have been studied, including the elements of neutron (n-) capture processes, as an important part of the enrichment sources of early Galaxy. Na, Mg, Al, Co, Sr, Y, Zr, Mo, Ba, La, Ce, Pr, Sm, Eu, Gd, Dy, Os, and Th abundances were determined using the synthetic spectrum method, taken into account the hyperfine structure (HFS) for the Ba II, La II and Eu II lines. The abundances of Si, Ca, Sc, N were determined based on the equivalent widths of their lines. The carbon abundance was obtained by the molecular synthesis fitting for the CH region of 4300-4330 ÅÅ. For the abundances determinations of C, Na, Mg, Al, Ba, and Th the NLTE corrections have been applied.We have determined the abundances of several n- capture elements for the first time and found that the behaviour of these elements abundances shows a significant trend with increasing atomic number. The elements ratios of [Eu/Fe] = 1.85, [Ba/Eu] = –1.24, [Sr/Ba] = –1.04 confirm the status of TYC5594-576-1 as a r-process enrichment star, with lower strontium [Sr/Fe] = –0.33 and higher thorium [Th/Fe] = 1.28 abundances. The obtained europium and thorium excesses testifies to the early enrichment of the Galaxy by the r-process elements as a result of the merger of neutron stars or black holes. The carbon abundance confirms the effect of canonical additional mixing in this star.

scholarly journals Using failed supernovae to constrain the Galactic r-process element production

2019 ◽  
Vol 487 (2) ◽  
pp. 1745-1753 ◽  
Author(s):  
B Wehmeyer ◽  
C Fröhlich ◽  
B Côté ◽  
M Pignatari ◽  
F-K Thielemann
Keyword(s):  
Black Hole ◽  
Neutron Star ◽  
Large Fraction ◽  
Capture Process ◽  
Compact Binary ◽  
Halo Stars ◽  
The Galaxy ◽  
Binary Mergers ◽  
R Process ◽  
Process Elements

ABSTRACT Rapid neutron capture process (r-process) elements have been detected in a large fraction of metal-poor halo stars, with abundances relative to iron (Fe) that vary by over two orders of magnitude. This scatter is reduced to less than a factor of 3 in younger Galactic disc stars. The large scatter of r-process elements in the early Galaxy suggests that the r-process is made by rare events, like compact binary mergers and rare sub-classes of supernovae. Although being rare, neutron star mergers alone have difficulties to explain the observed enhancement of r-process elements in the lowest metallicity stars compared to Fe. The supernovae producing the two neutron stars already provide a substantial Fe abundance where the r-process ejecta from the merger would be injected. In this work we investigate another complementary scenario, where the r-process occurs in neutron star-black hole mergers in addition to neutron star mergers. Neutron star-black hole mergers would eject similar amounts of r-process matter as neutron star mergers, but only the neutron star progenitor would have produced Fe. Furthermore, a reduced efficiency of Fe production from single stars significantly alters the age–metallicity relation, which shifts the onset of r-process production to lower metallicities. We use the high-resolution [(20 pc)3/cell] inhomogeneous chemical evolution tool ‘ICE’ to study the outcomes of these effects. In our simulations, an adequate combination of neutron star mergers and neutron star-black hole mergers qualitatively reproduces the observed r-process abundances in the Galaxy.

scholarly journals Abundance to age ratios in the HARPS-GTO sample with Gaia DR2

2019 ◽  
Vol 624 ◽  
pp. A78 ◽  
Author(s):  
E. Delgado Mena ◽  
A. Moya ◽  
V. Adibekyan ◽  
M. Tsantaki ◽  
J. I. González Hernández ◽  
...  
Keyword(s):  
Temporal Evolution ◽  
Thin Disk ◽  
Thick Disk ◽  
Clear Correlation ◽  
Chemical Abundances ◽  
Empirical Relations ◽  
Stellar Ages ◽  
Small Uncertainty ◽  
The Galaxy ◽  
Process Elements

Aims. The purpose of this work is to evaluate how several elements produced by different nucleosynthesis processes behave with stellar age and provide empirical relations to derive stellar ages from chemical abundances. Methods. We derived different sets of ages using Padova and Yonsei–Yale isochrones and HIPPARCOS and Gaia parallaxes for a sample of more than 1000 FGK dwarf stars for which he have high-resolution (R ~ 115 000) and high-quality spectra from the HARPS-GTO program. We analyzed the temporal evolution of different abundance ratios to find the best chemical clocks. We applied multivariable linear regressions to our sample of stars with a small uncertainty on age to obtain empirical relations of age as a function of stellar parameters and different chemical clocks. Results. We find that [α/Fe] ratio (average of Mg, Si, and Ti), [O/Fe] and [Zn/Fe] are good age proxies with a lower dispersion than the age-metallicity dispersion. Several abundance ratios present a significant correlation with age for chemically separated thin disk stars (i.e., low-α) but in the case of the chemically defined thick disk stars (i.e., high-α) only the elements Mg, Si, Ca, and Ti II show a clear correlation with age. We find that the thick disk stars are more enriched in light-s elements than thin disk stars of similar age. The maximum enrichment of s-process elements in the thin disk occurs in the youngest stars which in turn have solar metallicity. The slopes of the [X/Fe]-age relations are quite constant for O, Mg, Si, Ti, Zn, Sr, and Eu regardless of the metallicity. However, this is not the case for Al, Ca, Cu and most of the s-process elements, which display very different trends depending on the metallicity. This demonstrates the limitations of using simple linear relations based on certain abundance ratios to obtain ages for stars of different metallicities. Finally, we show that by using 3D relations with a chemical clock and two stellar parameters (either Teff, [Fe/H] or stellar mass) we can explain up to 89% of age variance in a star. A similar result is obtained when using 2D relations with a chemical clock and one stellar parameter, explaining up to a 87% of the variance. Conclusions. The complete understanding of how the chemical elements were produced and evolved in the Galaxy requires the knowledge of stellar ages and precise chemical abundances. We show how the temporal evolution of some chemical species change with metallicity, with remarkable variations at super-solar metallicities, which will help to better constrain the yields of different nucleosynthesis processes along the history of the Galaxy.

scholarly journals Neutron-capture elements in dwarf galaxies

2020 ◽  
Vol 641 ◽  
pp. A127 ◽  
Author(s):  
M. Reichert ◽  
C. J. Hansen ◽  
M. Hanke ◽  
Á. Skúladóttir ◽  
A. Arcones ◽  
...  
Keyword(s):  
Stellar Mass ◽  
Local Thermal Equilibrium ◽  
Universal Relation ◽  
Full Spectrum ◽  
The Galaxy ◽  
Type Ia ◽  
Ursa Minor ◽  
The Individual ◽  
Stellar Masses ◽  
Process Elements

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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