Related papers: Learning about the intermediate neutron-capture pr…
Carbon-enhanced metal-poor (CEMP) stars in the Galactic Halo display enrichments in heavy elements associated with either the s (slow) or the r (rapid) neutron-capture process (e.g., barium and europium respectively), and in some cases they…
Results from observations report a growing number of metal-poor stars showing an abundance pattern midway between the s- and r-processes. These so-called r/s-stars raise the need for an intermediate neutron capture process (i-process),…
We explore modifications to the current scenario for the slow neutron capture process in asymptotic giant branch (AGB) stars to account for the Pb deficiency observed in post-AGB stars of low metallicity ([Fe/H] ~ -1.2) and low initial mass…
Carbon-enhanced metal-poor (CEMP) r/s-stars show surface-abundance distributions characteristic of the so-called intermediate neutron capture process (i-process) of nucleosynthesis. We previously showed that the ingestion of protons in the…
We present models for the slow neutron-capture process (s process) in asymptotic giant branch (AGB) stars of metallicity [Fe/H]=-2.3 and masses 0.9 Msun to 6 Msun. We encountered different regimes of neutron-capture nucleosynthesis…
The surface chemical compositions of a large fraction of Carbon-Enhanced Metal-Poor (CEMP) stars, the so-called CEMP-r/s stars, are known to exhibit enhancement of both s- and r-process elements. For these stars, the heavy element…
Alongside the slow (s) and rapid (r) neutron capture processes, an intermediate neutron capture process (i-process) is thought to exist. It happens when protons are mixed in a convective helium-burning zone, and is referred to as proton…
We report abundance estimates for neutron-capture elements, including lead (Pb), and nucleosynthesis models for their origin, in two carbon-rich, very metal-poor stars, LP625-44 and LP706-7. These stars are subgiants whose surface…
The chemical abundances of the very metal-poor double-enhanced stars are excellent information for setting new constraints on models of neutron-capture processes at low metallicity. These stars are known as s+r stars, since they show…
We investigate whether the anomalous elemental abundance patterns in some of the C-enhanced metal-poor-s+r (CEMP-r/s) stars are consistent with predictions of nucleosynthesis yields from the i-process, a neutron-capture regime at neutron…
The determination of heavy element abundances from planetary nebula (PN) spectra provides an exciting opportunity to study the nucleosynthesis occurring in the progenitor asymptotic giant branch (AGB) star. We perform post-processing…
Context: Our understanding of the s-process nucleosynthesis in asymptotic giant branch (AGB) stars is incomplete. AGB models predict, for example, large overabundances of lead (Pb) compared to other s-process elements in metal-poor low-mass…
Around half of the heavy elements in the universe are formed through the slow neutron capture (s-) process, which takes place in thermally pulsing asymptotic giant branch (AGB) stars with masses $1-6\;M_{\odot}$. The nucleosynthetic imprint…
The intermediate neutron capture process (i-process) operates at neutron densities between those of the slow and rapid neutron-capture processes. It can be triggered by the ingestion of protons in a convective helium-burning region. One…
A large sample of carbon enhanced metal-poor stars enriched in s-process elements (CEMP-s) have been observed in the Galactic halo. These stars of low mass (M ~ 0.9 Msun) are located on the main-sequence or the red giant phase, and do not…
We report the detection of the Pb I 4057.8A line in the very metal-poor ([Fe/H]=-2.7), carbon-rich star, LP625-44. We determine the abundance of Pb ([Pb/Fe] = 2.65) and 15 other neutron-capture elements. The abundance pattern between Ba and…
To better characterize the abundance patterns produced by the r-process, we have derived new abundances or upper limits for the heavy elements zinc (Zn), yttrium (Y), lanthanum (La), europium (Eu), and lead (Pb). Our sample of 161…
By considering the various CEMP subclasses separately, we try to derive, from the specific signatures imprinted on the abundances, parameters (such as metallicity, mass, temperature, and neutron source) characterizing AGB nucleosynthesis…
Most heavy elements beyond the iron peak are synthesized via neutron capture processes. The nature of the astrophysical sites of neutron capture processes is still very unclear. In this work we explore the observational constraints of the…
This paper is part of a larger project in which we systematically study the chemical abundances of Galactic and extragalactic post-asymptotic giant branch (post-AGB) stars. Lead (Pb) is the final product of the s-process nucleosynthesis and…