Inhomogeneous chemical enrichment in the Galactic Halo

AbstractIn a galaxy, chemical enrichment takes place in an inhomogeneous fashion, and the Galactic Halo is one of the places where the inhomogeneous effects are imprinted and can be constrained from observations. I show this using my chemodynamical simulations of Milky Way type galaxies. The scatter in the elemental abundances originate from radial migration, merging/accretion of satellite galaxies, local variation of star formation and chemical enrichment, and intrinsic variation of nucleosynthesis yields. In the simulated galaxies, there is no strong age-metallicity relation. This means that the most metal-poor stars are not always the oldest stars, and can be formed in chemically unevolved clouds at later times. The long-lifetime sources of chemical enrichment such as asymptotic giant branch stars or neutron star mergers can contribute at low metallicities. The intrinsic variation of yields are important in the early Universe or metal-poor systems such as in the Galactic halo. The carbon enhancement of extremely metal-poor (EMP) stars can be best explained by faint supernovae, the low [α/Fe] ratios in some EMP stars naturally arise from low-mass (~ 13 - 15M⊙) supernovae, and finally, the [α/Fe] knee in dwarf spheroidal galaxies can be produced by subclasses of Type Ia supernovae such as SN 2002cx-like objects and sub-Chandrasekhar mass explosions.

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About the Chemical Evolution of dSphs (and the peculiar Globular Cluster ω Cen)

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308024733 ◽

2008 ◽

Vol 4 (S255) ◽

pp. 152-156 ◽

Cited By ~ 1

Author(s):

Andrea Marcolini ◽

Annibale D'Ercole

Keyword(s):

Chemical Evolution ◽

Globular Cluster ◽

Stellar System ◽

Three Dimensional ◽

Chemical Properties ◽

Dwarf Spheroidal Galaxies ◽

Chemical Enrichment ◽

Type Ia ◽

Hydrodynamical Simulations ◽

Ia Supernovae

AbstractWe present three dimensional hydrodynamical simulations aimed at studying the dynamical and chemical evolution of the interstellar medium (ISM) in isolated dwarf spheroidal galaxies (dSphs). This evolution is driven by the explosion of Type II and Type Ia supernovae, whose different contribution on both the dynamics and chemical enrichment is taken into account. Radiative losses are effective in radiating away the huge amount of energy released by SNe explosions, and the dSph is able to retain most of the gas allowing a long period (≥ 2 − 3 Gyr) of star formation, as usually observed in this kind of galaxies. We are able to reproduce the stellar metallicity distribution function (MDF) as well as the peculiar chemical properties of strongly O-depleted stars observed in several dSphs. The model also naturally predicts two different stellar populations, with an anti-correlation between [Fe/H] and velocity dispersion, similarly to what observed in the Sculptor and Fornax dSphs. These results derive from the inhomogeneous pollution of the SNe Ia, a distinctive characteristic of our model. We also applied the model to the peculiar globular cluster (GC) ω Cen in the hypothesis that it is the remnant of a formerly larger stellar system, possibly a dSph.

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Asteroseismology of luminous red giants with Kepler. II. Dependence of mass loss on pulsations and radiation

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3970 ◽

2020 ◽

Author(s):

Jie Yu ◽

Saskia Hekker ◽

Timothy R Bedding ◽

Dennis Stello ◽

Daniel Huber ◽

...

Keyword(s):

Mass Loss ◽

Mass Loss Rate ◽

Asymptotic Giant Branch ◽

Red Giants ◽

Asymptotic Giant Branch Stars ◽

Chemical Enrichment ◽

Dust Mass ◽

Red Giant ◽

The Masses ◽

Loss Rates

Abstract Mass loss by red giants is an important process to understand the final stages of stellar evolution and the chemical enrichment of the interstellar medium. Mass-loss rates are thought to be controlled by pulsation-enhanced dust-driven outflows. Here we investigate the relationships between mass loss, pulsations, and radiation, using 3213 luminous Kepler red giants and 135000 ASAS–SN semiregulars and Miras. Mass-loss rates are traced by infrared colours using 2MASS and WISE and by observed-to-model WISE fluxes, and are also estimated using dust mass-loss rates from literature assuming a typical gas-to-dust mass ratio of 400. To specify the pulsations, we extract the period and height of the highest peak in the power spectrum of oscillation. Absolute magnitudes are obtained from the 2MASS Ks band and the Gaia DR2 parallaxes. Our results follow. (i) Substantial mass loss sets in at pulsation periods above ∼60 and ∼100 days, corresponding to Asymptotic-Giant-Branch stars at the base of the period-luminosity sequences C′ and C. (ii) The mass-loss rate starts to rapidly increase in semiregulars for which the luminosity is just above the red-giant-branch tip and gradually plateaus to a level similar to that of Miras. (iii) The mass-loss rates in Miras do not depend on luminosity, consistent with pulsation-enhanced dust-driven winds. (iv) The accumulated mass loss on the Red Giant Branch consistent with asteroseismic predictions reduces the masses of red-clump stars by 6.3%, less than the typical uncertainty on their asteroseismic masses. Thus mass loss is currently not a limitation of stellar age estimates for galactic archaeology studies.

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Dust Production around Carbon-Rich Stars: The Role of Metallicity

Universe ◽

10.3390/universe7070233 ◽

2021 ◽

Vol 7 (7) ◽

pp. 233

Author(s):

Ambra Nanni ◽

Sergio Cristallo ◽

Jacco Th. van Loon ◽

Martin A. T. Groenewegen

Keyword(s):

Wind Speed ◽

Galactic Halo ◽

Magellanic Clouds ◽

Asymptotic Giant Branch ◽

Agb Stars ◽

Circumstellar Envelopes ◽

Chemical Enrichment ◽

Wide Range ◽

The Universe

Background: Most of the stars in the Universe will end their evolution by losing their envelope during the thermally pulsing asymptotic giant branch (TP-AGB) phase, enriching the interstellar medium of galaxies with heavy elements, partially condensed into dust grains formed in their extended circumstellar envelopes. Among these stars, carbon-rich TP-AGB stars (C-stars) are particularly relevant for the chemical enrichment of galaxies. We here investigated the role of the metallicity in the dust formation process from a theoretical viewpoint. Methods: We coupled an up-to-date description of dust growth and dust-driven wind, which included the time-averaged effect of shocks, with FRUITY stellar evolutionary tracks. We compared our predictions with observations of C-stars in our Galaxy, in the Magellanic Clouds (LMC and SMC) and in the Galactic Halo, characterised by metallicity between solar and 1/10 of solar. Results: Our models explained the variation of the gas and dust content around C-stars derived from the IRS Spitzer spectra. The wind speed of the C-stars at varying metallicity was well reproduced by our description. We predicted the wind speed at metallicity down to 1/10 of solar in a wide range of mass-loss rates.

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On the Typical Timescale for the Chemical Enrichment from Type Ia Supernovae in Galaxies

The Astrophysical Journal ◽

10.1086/322472 ◽

2001 ◽

Vol 558 (1) ◽

pp. 351-358 ◽

Cited By ~ 229

Author(s):

Francesca Matteucci ◽

Simone Recchi

Keyword(s):

Type Ia Supernovae ◽

Chemical Enrichment ◽

Type Ia ◽

Ia Supernovae

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Unusual neutron-capture nucleosynthesis in a carbon-rich Galactic bulge star

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834241 ◽

2019 ◽

Vol 622 ◽

pp. A159 ◽

Cited By ~ 3

Author(s):

Andreas Koch ◽

Moritz Reichert ◽

Camilla Juul Hansen ◽

Melanie Hampel ◽

Richard J. Stancliffe ◽

...

Keyword(s):

Neutron Capture ◽

Galactic Halo ◽

Asymptotic Giant Branch ◽

Galactic Bulge ◽

Element Abundances ◽

Intermediate Neutron ◽

Low Mass ◽

Process Component ◽

Process Elements ◽

The Impact

Metal-poor stars in the Galactic halo often show strong enhancements in carbon and/or neutron-capture elements. However, the Galactic bulge is notable for its paucity of these carbon-enhanced metal-poor (CEMP) and/or CH-stars, with only two such objects known to date. This begs the question whether the processes that produced their abundance distribution were governed by a comparable nucleosynthesis in similar stellar sites as for their more numerous counterparts in the halo. Recently, two contenders of these classes of stars were discovered in the bulge, at [Fe/H] = −1.5 and −2.5 dex, both of which show enhancements in [C/Fe] of 0.4 and 1.4 dex (respectively), [Ba/Fe] in excess of 1.3 dex, and also elevated nitrogen. The more metal-poor of the stars can be well matched by standard s-process nucleosynthesis in low-mass asymptotic giant branch (AGB) polluters. The other star shows an abnormally high [Rb/Fe] ratio. Here, we further investigate the origin of the abundance peculiarities in the Rb-rich star by new, detailed measurements of heavy element abundances and by comparing the chemical element ratios of 36 species to several models of neutron-capture nucleosynthesis. The i-process with intermediate neutron densities between those of the slow (s-) and rapid (r)-neutron-capture processes has been previously found to provide good matches of CEMP stars with enhancements in both r- and s-process elements (class CEMP-r/s), rather than invoking a superposition of yields from the respective individual processes. However, the peculiar bulge star is incompatible with a pure i-process from a single ingestion event. Instead, it can, statistically, be better reproduced by more convoluted models accounting for two proton ingestion events, or by an i-process component in combination with s-process nucleosynthesis in low-to-intermediate mass (2–3 M⊙) AGB stars, indicating multiple polluters. Finally, we discuss the impact of mixing during stellar evolution on the observed abundance peculiarities.

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Asymptotic Giant Branch Variables in Nearby Galaxies

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318006415 ◽

2018 ◽

Vol 14 (S343) ◽

pp. 275-282

Author(s):

Patricia A. Whitelock

Keyword(s):

Large Amplitude ◽

Mass Scale ◽

Asymptotic Giant Branch ◽

Infrared Observations ◽

Chemical Enrichment ◽

Mira Variables ◽

James Webb Space Telescope ◽

Distant Galaxies ◽

Nearby Galaxies ◽

Low Mass

AbstractCertain types of large amplitude AGB variable are proving to be powerful distance indicators that will rival Cepheids in the James Webb Space Telescope era of high precision infrared photometry. These are predominantly found in old populations and have low mass progenitors. At the other end of the AGB mass-scale, large amplitude variables, particularly those undergoing hot bottom burning, are the most luminous representatives of their population. These stars are < 1 Gyr old, are often losing mass copiously and are vital to our understanding of the integrated light of distant galaxies as well as to chemical enrichment. However, the evolution of such very luminous AGB variables is rapid and remains poorly understood. Here I discuss recent infrared observations of both low- and intermediate-mass Mira variables in the Local Group and beyond.

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Evolution and Nucleosynthesis in Low‐Mass Asymptotic Giant Branch Stars. I. Formation of Population I Carbon Stars

The Astrophysical Journal ◽

10.1086/303794 ◽

1997 ◽

Vol 478 (1) ◽

pp. 332-339 ◽

Cited By ~ 187

Author(s):

Oscar Straniero ◽

Alessandro Chieffi ◽

Marco Limongi ◽

Maurizio Busso ◽

Roberto Gallino ◽

...

Keyword(s):

Asymptotic Giant Branch ◽

Asymptotic Giant Branch Stars ◽

Carbon Stars ◽

Low Mass ◽

Giant Branch Stars

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High-resolution Keck I spectroscopy of Galactic halo post-asymptotic giant branch stars

Monthly Notices of the Royal Astronomical Society ◽

10.1046/j.1365-8711.2002.05912.x ◽

2002 ◽

Vol 337 (3) ◽

pp. 851-860 ◽

Cited By ~ 15

Author(s):

C. J. Mooney ◽

W. R. J. Rolleston ◽

F. P. Keenan ◽

P. L. Dufton ◽

J. V. Smoker ◽

...

Keyword(s):

High Resolution ◽

Galactic Halo ◽

Asymptotic Giant Branch ◽

Asymptotic Giant Branch Stars ◽

Giant Branch Stars

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Abundance Ratios in Metal-Poor Globular Clusters: Deep Mixing and its Effect on Stellar Populations of the Galactic Halo

Highlights of Astronomy ◽

10.1017/s1539299600019961 ◽

1998 ◽

Vol 11 (1) ◽

pp. 53-57

Author(s):

Robert P. Kraft

Keyword(s):

Globular Clusters ◽

Galactic Halo ◽

Light Element ◽

Asymptotic Giant Branch ◽

Proton Capture ◽

Low Mass Stars ◽

Element Abundances ◽

Deep Mixing ◽

Low Mass ◽

Red Giant

Only a bit more than 25 years ago, it seemed possible to assume that all Galactic globular clusters were chemically homogeneous. There were indications that star-to-star Fe abundance variations existed in ω Cen, but this massive cluster appeared to be unique. Following Osborn’s (1971) initial discovery, Zinn’s (1973) observation that M92 asymptotic giant branch (AGB) stars had weaker G-bands than subgiants with equivalent temperatures provided the first extensive evidence that there might be variations in the abundances of the light elements in an otherwise “normal” cluster. Since then star-to-star variations in the abundances of C, N, O, Na, Mg and Al have been observed in all cases in which sample sizes have exceeded 5-10 stars, e.g., in clusters such as M92, M15, M13, M3, ω Cen, MIO and M5. Among giants in these clusters one finds large surface O abundance differences, and these are intimately related to differences of other light element abundances, not only of C and N, but also of Na, Mg and Al (cf. reviews by Suntzeff 1993, Briley et al 1994, and Kraft 1994). The abundances of Na and O, as well as Al and Mg, are anticorrelated. Prime examples are found among giants in M15 (Sneden et al 1997), M13 (Pilachowski et al 1996; Shetrone 1996a,b; and Kraft et al 1997) and ω Cen (Norris & Da Costa 1995a,b). These observed anticorrelations almost certainly result from proton- capture chains that convert C to N, 0 to N, Ne to Na and Mg to Al in or near the hydrogen fusion layers of evolved cluster stars. But which stars? An appealing idea is that during the giant branch lifetimes of the low-mass stars that we now observe, substantial portions of the stellar envelopes have been cycled through regions near the H-burning shell where proton-capture nucleosynthesis can occur. This so-called “evolutionary” scenario involving deep envelope mixing in first ascent red giant branch (RGB) stars has been studied by Denissenkov & Denissenkova (1990), Langer & Hoffman (1995), Cavallo et al (1996, 1997) and Langer et al (1997). The mixing mechanism that brings proton-capture products to the surface is poorly understood (Denissenkov & Weiss 1996, Denissenkov et al 1997, Langer et al 1997), but deep mixing driven by angular momentum has been suggested (Sweigart & Mengel 1979, Kraft 1994, Langer & Hoffman 1995, Sweigart 1997).

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