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
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
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, 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
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
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
M. Saberi, T. Khouri, L. Velilla-Prieto, J. P. Fonfria, W. H. T. Vlemmings, S. Wedemeyer
Summary: The paper reports observations of aluminum monofluoride (AlF) line emission towards five nearby oxygen-rich AGB stars. By using ALMA observations, the emitting region of AlF for o Ceti and R Leo was estimated. Population diagram analysis was used to estimate the AlF column densities, revealing consistency with the solar F budget.
ASTRONOMY & ASTROPHYSICS
(2022)
Review
Astronomy & Astrophysics
Nan Liu, Sergio Cristallo, Diego Vescovi
Summary: Studying the isotopes of presolar grains, especially heavy element isotopes, is crucial for nuclear astrophysics. By analyzing the abundances in presolar grains, we can obtain independent and detailed constraints on stellar parameters.
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)
