Jennifer Sanchez Rojo
Gather.town id
CCE08
Poster Title
Triggering rp-process nucleosynthesis on neutron stars in binary systems through alpha capture on oxygen-15
Institution
University of York
Abstract (short summary)
The astrophysical oxygen-15 alpha capture reaction [1] is a key breakout route from the Hot CNO cycle leading to explosive nucleosynthesis via the rp-process on the surface of neutron stars in binary systems. Determining an accurate cross section for the relevant states is critical for a better understanding of the X-ray burst energy production and light-curves [2], as well as other novel binary stellar systems involving neutron stars and their potential impact on nucleosynthesis [3].
An indirect alpha transfer reaction in inverse kinematics has been performed, populating the relevant states at temperatures up to 1GK. In this, we take advantage of the 15O Radioactive Ion Beam provided at GANIL and the state-of-the art detection system VAMOS + AGATA + MUGAST coupled together for the first time [4], allowing us an unrivalled selectivity for detecting triple coincidences in this reaction. We will present the experimental set-up and analysis, as well as preliminary results for the strongest populated resonances in 19Ne.
[1] M. R. Hall et al. Phys. Rev. C 99, 035805 (2019)
[2] R. H. Cyburt et al. Astrophys. J. 830, 55 (2016)
[3] J. Keegans et al. MNRAS, V. 485, Issue 1, Pages 620–639 (2019)
[4] M. Assié et al. Accepted for publication in NIMA (2021)
An indirect alpha transfer reaction in inverse kinematics has been performed, populating the relevant states at temperatures up to 1GK. In this, we take advantage of the 15O Radioactive Ion Beam provided at GANIL and the state-of-the art detection system VAMOS + AGATA + MUGAST coupled together for the first time [4], allowing us an unrivalled selectivity for detecting triple coincidences in this reaction. We will present the experimental set-up and analysis, as well as preliminary results for the strongest populated resonances in 19Ne.
[1] M. R. Hall et al. Phys. Rev. C 99, 035805 (2019)
[2] R. H. Cyburt et al. Astrophys. J. 830, 55 (2016)
[3] J. Keegans et al. MNRAS, V. 485, Issue 1, Pages 620–639 (2019)
[4] M. Assié et al. Accepted for publication in NIMA (2021)
Plain text (extended) Summary
Triggering rp-process nucleosynthesis on neutron stars in binary systems through alpha capture on oxygen-15.
Neutron stars in binary systems are sites of very fast and violent explosions that emit flashes of light called X-ray bursts. We have studied the oxygen-15 plus alpha reaction to determine its role in the ignition of the rp-process. This reaction acts as a bottleneck between the HCNO cycle and the nucleosynthesis of heavier elements in neutron star surfaces.
The astrophysical scenario subject of this study is accreting neutron stars where a neutron star in a binary system will attract material from its companion causing an increase of temperature and pressure on the surface of the neutron star, and the ignition of hydrogen burning through the hot-CNO cycle. When the temperature is hot enough, other nuclear reactions are activated. This leads to a breakout from the hot-CNO cycle after the capture of an α particle, leading to thermonuclear runaways that emit flashes of light called X-ray bursts.
The alpha capture reaction on oxygen-15 is key to understanding the reaction mechanism of the produced X-ray bursts. It regulates the flow between the hot-CNO cycle and the rp-process. The production of heavier elements depends on the ratio between the alpha capture and the beta decay. Many sensitivity studies have pointed out that the observed light curves from X-ray bursts depend on this reaction rate. Hence, we need a better determination of the alpha capture rate.
We need to understand the properties of this nuclear reaction to determine its reaction rate and to constrain the models. For this reason the neon-19 isotope is very important. Studying the properties of the neon-19 resonances allows us to calculate the reaction rate. The 4.03 MeV excited state is the biggest contribution of the rate, and it is very difficult to constrain due to its small cross section.
For this study, we performed an alpha transfer reaction populating the neon-19 excited states for temperatures up to 1GK. Our aim was to populate the 4.03 MeV state. We used the VAMOS AGATA and MUGAST setup at GANIL, France. With this set of detectors we were able to detect the neon-19 recoils, the gamma rays from the de-excitation, and the ejected light particles. In this way we isolated the alpha transfer reaction by selecting the three detected particles in coincidence. With our selectivity we measured 3 candidates of alpha transfer on the 4.03 MeV state. A gamma ray spectrum is shown with the gamma rays obtained for the alpha transfer, doing the coincidences between the detected neon-19 recoils and the tritons. In the region of approximately 4 MeV we can see three events: our three candidates.
From this result, we estimated a preliminary value for the cross section of 3.6 micro barns, including its statistical error of plus 3.5 and minus 1.9 micro barns.
This experiment has achieved a better selectivity than previous work.
Our next step is the determination of the alpha width of the 4.03 MeV level in neon-19. From this result, we will obtain its reaction rate and we will, then, implement the obtained rate and its uncertainty in the X-ray burst models, constraining them and helping to go a step further in the understanding of this phenomenon that has been studied for over 40 years.
Neutron stars in binary systems are sites of very fast and violent explosions that emit flashes of light called X-ray bursts. We have studied the oxygen-15 plus alpha reaction to determine its role in the ignition of the rp-process. This reaction acts as a bottleneck between the HCNO cycle and the nucleosynthesis of heavier elements in neutron star surfaces.
The astrophysical scenario subject of this study is accreting neutron stars where a neutron star in a binary system will attract material from its companion causing an increase of temperature and pressure on the surface of the neutron star, and the ignition of hydrogen burning through the hot-CNO cycle. When the temperature is hot enough, other nuclear reactions are activated. This leads to a breakout from the hot-CNO cycle after the capture of an α particle, leading to thermonuclear runaways that emit flashes of light called X-ray bursts.
The alpha capture reaction on oxygen-15 is key to understanding the reaction mechanism of the produced X-ray bursts. It regulates the flow between the hot-CNO cycle and the rp-process. The production of heavier elements depends on the ratio between the alpha capture and the beta decay. Many sensitivity studies have pointed out that the observed light curves from X-ray bursts depend on this reaction rate. Hence, we need a better determination of the alpha capture rate.
We need to understand the properties of this nuclear reaction to determine its reaction rate and to constrain the models. For this reason the neon-19 isotope is very important. Studying the properties of the neon-19 resonances allows us to calculate the reaction rate. The 4.03 MeV excited state is the biggest contribution of the rate, and it is very difficult to constrain due to its small cross section.
For this study, we performed an alpha transfer reaction populating the neon-19 excited states for temperatures up to 1GK. Our aim was to populate the 4.03 MeV state. We used the VAMOS AGATA and MUGAST setup at GANIL, France. With this set of detectors we were able to detect the neon-19 recoils, the gamma rays from the de-excitation, and the ejected light particles. In this way we isolated the alpha transfer reaction by selecting the three detected particles in coincidence. With our selectivity we measured 3 candidates of alpha transfer on the 4.03 MeV state. A gamma ray spectrum is shown with the gamma rays obtained for the alpha transfer, doing the coincidences between the detected neon-19 recoils and the tritons. In the region of approximately 4 MeV we can see three events: our three candidates.
From this result, we estimated a preliminary value for the cross section of 3.6 micro barns, including its statistical error of plus 3.5 and minus 1.9 micro barns.
This experiment has achieved a better selectivity than previous work.
Our next step is the determination of the alpha width of the 4.03 MeV level in neon-19. From this result, we will obtain its reaction rate and we will, then, implement the obtained rate and its uncertainty in the X-ray burst models, constraining them and helping to go a step further in the understanding of this phenomenon that has been studied for over 40 years.
URL
jsr539@york.ac.uk, twitter: @jennsrojo
Poster file