Article
Astronomy & Astrophysics
Pavel A. Denissenkov, Falk Herwig, Georgios Perdikakis, Hendrik Schatz
Summary: This study investigates the impact of (n,gamma) reaction rate uncertainties on the predicted abundances of neutron-capture elements in carbon-enhanced metal-poor stars, finding that certain reactions have significant effects on the predicted abundances of barium and praseodymium.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
D. Kamath, F. Dell'Agli, P. Ventura, H. Van Winckel, S. Tosi, A. Karakas
Summary: We study a sample of single Galactic post-AGB stars to determine their initial masses, chemical compositions, and progenitor ages. The luminosity and surface carbon abundance prove to be the most valuable indicators of the star's previous evolution and nucleosynthetic history. This allows us to classify the post-AGB sample into different classes based on their evolutionary history on the AGB. The analysis sheds new light on debated issues related to AGB evolution and nucleosynthesis.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Giulia C. Cinquegrana, Amanda Karakas
Summary: As metallicity increases, the mixing efficiency on the TP-AGB decreases significantly, leading to much of the nucleosynthesis being locked inside white dwarf remnants for very metal-rich stars. Additionally, temperatures at the base of the convective envelope decrease with increasing metallicity, resulting in only partial hydrogen burning for intermediate-mass models. Minor production of heavy elements via the s-process peak at strontium is found in the study, which decreases sharply with increasing metallicity. The dominance of proton capture nucleosynthesis in the models is reflected in the yields, weighted towards the lower mass regime to match the mass distribution within a galaxy.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
A. Choplin, S. Goriely, L. Siess
Summary: This study explores the possibility of low-mass low-metallicity AGB stars synthesizing actinides through the intermediate neutron capture process (i-process). A 1 M-circle dot model is used to compute the surface abundance, and it is found that the model can reproduce the Th abundance of star RAVE J094921.8-161722. This finding has implications for dating CEMP-r/s stars.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
A. Choplin, L. Siess, S. Goriely
Summary: This study investigates the possibility of i-process nucleosynthesis in low-metallicity low-mass stars during the early stages of the asymptotic giant branch (AGB) phase, in order to explain the abundance patterns of r/s-stars. Results show that the i-process elemental distribution is not strongly affected by the temporal and spatial resolution used to compute the stellar models, but there are typical uncertainties in individual abundances of approximately +/- 0.3 dex. Specific isotopic ratios of certain elements can serve as good tracers of i-process nucleosynthesis.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
S. Goriely, L. Siess, A. Choplin
Summary: This study explores the impact of nuclear uncertainties on the i-process of nucleosynthesis in low-metallicity low-mass stars during the asymptotic giant branch phase. It finds that systematic uncertainties in radiative neutron capture rates can significantly affect surface elemental abundances, with some elements being less affected than others. Improvements in direct neutron capture descriptions and constraints on photon strength functions and nuclear level densities could enhance the predictive power of simulations in this area.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
Amanda Karakas, Giulia Cinquegrana, Meridith Joyce
Summary: New stellar evolutionary sequences of very metal-rich stars are presented using the Monash Stellar Structure code and mesa. The study reveals that metallicity has a weaker influence on hot bottom burning, while it significantly affects core mass instabilities and minimum mass for carbon ignition.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
A. Yague Lopez, D. A. Garcia-Hernandez, P. Ventura, C. L. Doherty, J. W. den Hartogh, S. W. Jones, M. Lugaro
Summary: This study describes the first s-process post-processing models for asymptotic giant branch (AGB) stars of masses 3, 4, and 5 solar masses at solar metallicity. The results show that the high abundance of C-12 in the He-rich intershell in ATON results in an s-process abundance pattern that favors the second peak over the first peak.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
B. Cseh, B. Vilagos, M. P. Roriz, C. B. Pereira, V D'Orazi, A. Karakas, B. Soos, N. A. Drake, S. Junqueira, M. Lugaro
Summary: This study compares the abundance patterns of Ba stars to AGB nucleosynthesis models and verifies the compatibility between AGB model mass and independently derived AGB mass. The results indicate that most Ba stars are contaminated by low-mass, non-rotating AGB stellar models, and some observed elemental abundances are higher than the predicted values. Some stars may have lower masses than independently determined.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
M. P. Roriz, C. B. Pereira, S. Junqueira, M. Lugaro, N. A. Drake, C. Sneden
Summary: We present detailed chemical compositions of four chemically peculiar stars on the first-ascent red giant branch, which lack high spectral resolution comprehensive analyses. These stars, BD+03 degrees 2688, HE 0457-1805, HE 1255-2324, and HE 2207-1746, exhibit a range in Galactic population membership with metallicities of [Fe/H] = -1.21, -0.19, -0.31, and -0.55, respectively. We obtained elemental abundances for 28 elements, including CNO group and C-12/C-13 ratios, as well as novel results for the heavy elements tungsten and thallium. All four stars show significant enhancements of neutron-capture elements, indicating enrichments from the slow neutron capture (s-process).
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
P. Krynski, L. Siess, A. Jorissen
Summary: This study proposes a fictitious network to approximate the synthesis of ls, hs, and vhs species in AGB stars with minimal computational expense. The network consists of seven fictitious particles assembled from elements with Z≥18, and their abundances and reaction rates are used to model the effective properties of the corresponding groups. The results show that the fictitious network reliably reproduces the abundances of ls, hs, and vhs species during the radiative s-process.
ASTRONOMY & ASTROPHYSICS
(2023)
Article
Astronomy & Astrophysics
D. Vescovi, S. Cristallo, S. Palmerini, C. Abia, M. Busso
Summary: Magnetic buoyancy plays a crucial role in AGB stellar models, where F-19 is mainly produced through nucleosynthesis involving secondary N-14 during convective thermal pulses rather than from N-14 in the C-13 pocket region, resulting in lower fluorine surface abundances.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
Umberto Battino, Claudia Lederer-Woods, Marco Pignatari, Benjamin Soos, Maria Lugaro, Diego Vescovi, Sergio Cristallo, Philip J. Woods, Amanda Karakas
Summary: This study re-evaluates the production of Al-26 and its impact on stellar nucleosynthesis. The new reactivities have a significant effect on both low- and high-mass stars.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
D. Karinkuzhi, S. Van Eck, S. Goriely, L. Siess, A. Jorissen, T. Merle, A. Escorza, T. Masseron
Summary: The study proposes a more robust classification method for CEMP-s and CEMP-rs stars using heavy elements other than Ba and Eu. It suggests that the abundance patterns of CEMP-rs stars can be well explained by low-metallicity 1 M-circle dot models experiencing proton ingestion.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
Shreeya Shetye, Sophie Van Eck, Alain Jorissen, Stephane Goriely, Lionel Siess, Hans Van Winckel, Bertrand Plez, Michel Godefroid, George Wallerstein
Summary: The study aims to investigate the evolutionary status of Tc-rich S stars by locating them in a Hertzsprung-Russell diagram, using Gaia Early Data Release 3. It combines a sample of Tc-rich stars to determine the onset of the third dredge-up, and compares abundance determinations with AGB nucleosynthesis predictions. The results show that intrinsic S stars are consistent with being genuine TP-AGB stars, and the s-process abundance profiles align well with nucleosynthesis predictions. Stars with highest [s/Fe] tend to have the highest C/O ratios.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
Alex J. Kemp, Amanda Karakas, Andrew R. Casey, Chiaki Kobayashi, Robert G. Izzard
Summary: The study reveals a clear anticorrelation between metallicity and the number of novae produced, with fewer novae at higher metallicities. The white dwarf mass distribution shows a systematic variation with metallicity, while the shape of the accretion rate distribution remains relatively stable. The predicted nova rates in the Milky Way and M31 are consistent with observational estimates, but the shape of the white dwarf mass distribution differs significantly from existing observations.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Amanda Karakas, Giulia Cinquegrana, Meridith Joyce
Summary: New stellar evolutionary sequences of very metal-rich stars are presented using the Monash Stellar Structure code and mesa. The study reveals that metallicity has a weaker influence on hot bottom burning, while it significantly affects core mass instabilities and minimum mass for carbon ignition.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Giulia C. Cinquegrana, Amanda Karakas
Summary: As metallicity increases, the mixing efficiency on the TP-AGB decreases significantly, leading to much of the nucleosynthesis being locked inside white dwarf remnants for very metal-rich stars. Additionally, temperatures at the base of the convective envelope decrease with increasing metallicity, resulting in only partial hydrogen burning for intermediate-mass models. Minor production of heavy elements via the s-process peak at strontium is found in the study, which decreases sharply with increasing metallicity. The dominance of proton capture nucleosynthesis in the models is reflected in the yields, weighted towards the lower mass regime to match the mass distribution within a galaxy.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Stephanie Monty, David Yong, Anna F. Marino, Amanda Karakas, Madeleine McKenzie, Frank Grundahl, Aldo Mura-Guzman
Summary: Using differential abundance analysis, this study reveals the presence of multiple chemical peculiarities in the globular clusters NGC 288 and NGC 362. The measurements of 20 elements showed differential uncertainties ranging from 0.01 to 0.02 dex in both clusters. The analysis found dispersion in the abundances of various elements in both clusters, with NGC 362 demonstrating additional dispersion in some elements.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Kate A. Womack, Fiorenzo Vincenzo, Brad K. Gibson, Benoit Cote, Marco Pignatari, Hannah E. Brinkman, Paolo Ventura, Amanda Karakas
Summary: By comparing chemical evolution models to observations of fluorine abundances in Milky Way stars, researchers have identified the significant impact of rotational velocity of massive stars on the chemical evolution of fluorine. They also predict the importance of metal-rich stars, such as pollution stars, in the evolution of fluorine.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
D. Kamath, F. Dell'Agli, P. Ventura, H. Van Winckel, S. Tosi, A. Karakas
Summary: We study a sample of single Galactic post-AGB stars to determine their initial masses, chemical compositions, and progenitor ages. The luminosity and surface carbon abundance prove to be the most valuable indicators of the star's previous evolution and nucleosynthetic history. This allows us to classify the post-AGB sample into different classes based on their evolutionary history on the AGB. The analysis sheds new light on debated issues related to AGB evolution and nucleosynthesis.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
L. Mashonkina, A. Arentsen, D. S. Aguado, A. Smogorzhevskii, M. Hampel, A. Karakas, F. Sestito, N. F. Martin, K. A. Venn, J. I. Gonzalez Hernandez
Summary: This study presents high-resolution spectroscopic follow-up of the carbon-enhanced metal-poor star Pristine 184237. The atmospheric parameters and abundances for 32 elements were determined, revealing unique element abundance patterns. It is the first star of the CEMP-r/s subclass identified in the inner Galaxy.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Stephanie Monty, David Yong, Davide Massari, Madeleine McKenzie, GyuChul Myeong, Sven Buder, Amanda Karakas, Ken C. Freeman, Anna F. Marino, Vasily Belokurov, N. Wyn Evans
Summary: By comparing the chemical abundances of globular clusters NGC 362 and NGC 288, we find strong similarities between them but marked differences when compared to the Gaia-Sausage-Enceladus (GSE) stars. This suggests that NGC 362 and NGC 288 are either not galactic siblings or that GSE had enough chemical inhomogeneity to produce two similar yet distinct clusters with different chemistry compared to constituent stars.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Boquan Chen, Michael R. Hayden, Sanjib Sharma, Joss Bland-Hawthorn, Chiaki Kobayashi, Amanda Karakas
Summary: We propose a multizone galactic chemical evolution model that considers the most recently updated nucleosynthesis yields. The model incorporates physical processes such as gas feedback, radial flow of gas, infall of fresh gas, and radial migration. We analyze the impact of these processes on the observed properties of the Milky Way. The model successfully reproduces the observed distribution of stars in terms of metallicity and alpha-to-iron ratio.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Tuila Ziliotto, Antonino Milone, Anna F. F. Marino, Aaron L. L. Dotter, Alvio Renzini, Enrico Vesperini, Amanda Karakas, Giacomo Cordoni, Emanuele Dondoglio, Maria V. V. Legnardi, Edoardo P. P. Lagioia, Anjana Mohandasan, Sarah Baimukhametova
Summary: Recent studies have shown the theoretical behavior of multiple populations in metal-intermediate globular clusters using the JWST. These findings are supported by observations of multiple populations in M dwarfs. In this study, the authors explore multiple populations in metal-poor GCs and identify distinct stellar populations using synthetic spectra and isochrones. The researchers find that the helium abundances of second-generation stars are higher than those of the first generation, and that the color-magnitude diagram shows a wide color broadening due to multiple populations.
ASTROPHYSICAL JOURNAL
(2023)
Article
Astronomy & Astrophysics
Giulia C. Cinquegrana, Meridith Joyce, Amanda Karakas
Summary: The study investigates the minimum mass required for a star to undergo an Fe core collapse supernova in super metal-rich models. It is found that the minimum initial mass for Fe core collapse is lower in super metal-rich models compared to solar metallicity. This has implications for accurately modeling supernovae rates as a function of metallicity in galactic chemical evolution simulations, particularly for metal-rich spiral and elliptical galaxies.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Jianhui Lian, Nicholas Storm, Guillaume Guiglion, Aldo Serenelli, Benoit Cote, Amanda Karakas, Nicholas Boardman, Maria Bergemann
Summary: By studying the chemical abundances of stars, the locations of neutron capture processes have been investigated. For r-process elements, the distribution of the ratio of Europium to Iron suggests a short delay time of the site that produces Europium, but other independent observations suggest a significant fraction of long delayed neutron star mergers. Including short delayed r-process sites can resolve this inconsistency. For s-process elements, the ratio of Barium to Yttrium shows weak metallicity dependence, suggesting that the s-process efficiency of low-mass AGB stars in current models may be overestimated.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
David Yong, Fan Liu, Yuan-Sen Ting, Meridith Joyce, Bertram Bitsch, Fei Dai, Aaron Dotter, Amanda I. Karakas, Michael T. Murphy
Summary: This study conducts a line-by-line differential analysis of 125 co-moving pairs of stars and obtains high-precision stellar parameters. These stars are classified into chemically homogeneous and inhomogeneous groups. The study reveals the relationship between separation, effective temperature, and chemically homogeneous pairs. The importance of this study lies in the discovery of a sample of bright co-moving pairs with chemical abundance differences comparable to that of the Hyades open cluster, which can be used for calibrating stellar abundances in large-scale spectroscopic surveys.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Zara Osborn, Amanda Karakas, Alex J. Kemp, Robert G. Izzard
Summary: In this study, the impact of binary evolution on Al-26 yields is explored. It is found that the key condition for achieving the most overproduction of Al-26 is for stars to have small cores relative to their total masses when entering the TP-AGB phase. The population with a binary fraction of 0.75 shows a 25% increase in Al-26 weighted population yield compared to the population of single-stars only. Further analysis of the stellar interior structure supports these results.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
A. F. Marino, A. P. Milone, E. Dondoglio, A. Renzini, G. Cordoni, H. Jerjen, A. Karakas, E. P. Lagioia, M. V. Legnardi, M. McKenzie, A. Mohandasan, M. Tailo, D. Yong, T. Ziliotto
Summary: Chromosome maps of globular clusters reveal the inhomogeneity of metallicity in these ancient structures. Type II clusters show larger variations, possibly due to multiple generations of stars. Most clusters also have inhomogeneous first generation stars, pointing towards a not fully mixed molecular cloud.
ASTROPHYSICAL JOURNAL
(2023)