The final stages of the evolution of electron--degenerate ONe cores, resulting from carbon burnin... more The final stages of the evolution of electron--degenerate ONe cores, resulting from carbon burning in ``heavy weight'' intermediate--mass stars ($8 M_{\sun}\la M \la 11 M_{\sun}$) and growing in mass, either from carbon burning in a shell or from accretion of matter in a close binary system, are examined in the light of their detailed chemical composition. In particular, we have modelled the evolution taking into account the abundances of the following minor nuclear species, which result from the previous evolutionary history: $^{12}$C, $^{23}$Na, $^{24}$Mg, and $^{25}$Mg. Both $^{23}$Na and $^{25}$Mg give rise to Urca processes, which are found to be unimportant for the final outcome of the evolution. $^{24}$Mg was formerly considered a major component of ONe cores (hence called ONeMg cores), but updated evolutionary calculations in this mass range have severely reduced its abundance. Nevertheless, we have parameterized it and we have found that the minimum amount of $^{24}$Mg required to produce NeO burning at moderate densities is $\sim 23%$, a value exceedingly high in the light of recent evolutionary models. Finally, we have determined that models with relatively small abundances of unburnt carbon ($X(^{12}$C)$\sim 0.015$) could be a channel to explosion at low to moderate density ($\sim 1\times 10^9$ g cm$^{-3}$). This is clearly below the current estimate for the explosion/collapse threshold and would have interesting consequences.
We compute and analyze the evolution of primordial stars of masses at the ZAMS between 5 M_sun an... more We compute and analyze the evolution of primordial stars of masses at the ZAMS between 5 M_sun and 10 M_sun, with and without overshooting. Our main goals are to determine the nature of the remnants of massive intermediate-mass primordial stars and to check the influence of overshooting in their evolution. Our calculations cover stellar evolution from the main sequence phase until the formation of the degenerate cores and the thermally pulsing phase. We have obtained the values for the limiting masses of Population III progenitor stars leading to carbon-oxygen and oxygen-neon compact cores. Moreover, we have also obtained the limiting mass for which isolated primordial stars would lead to core-collapse supernovae after the end of the main central burning phases. Considering a moderate amount of overshooting the mass thresholds at the ZAMS for the formation of carbon-oxygen and oxygen-neon degenerate cores shifts to smaller values by about 2 M_sun. As a by-product of our calculations, we have also obtained the structure and composition profiles of the resulting compact remnants. Opposite to what happens with solar metallicity objects, the final fate of primordial stars is not straightforward determined from the mass of the compact cores at the end of carbon burning. Instead, the small mass-loss rates typically associated to stellar winds of low metallicity stars might allow the growth of the resulting degenerate cores up to the Chandrasekhar mass, on time scales one or two orders of magnitude shorter than the time required to loose the envelope. This would lead to the formation of supernovae for initial masses as small as about 5 M_sun.
First Steps in the Origin of Life in the Universe, Jan 1, 2001
ABSTRACT The study of the origin of life on the Earth is impeded by the fact that very few ancien... more ABSTRACT The study of the origin of life on the Earth is impeded by the fact that very few ancient rocks from the era of the appearance of biological systems are preserved. The oldest sedimentary rock formations are about 3.9 billion years old, and even these show indications of the early emergence of life. Impacts, tectonic activity and erosion have hopelessly destroyed all the information predating the aforementioned age. Nevertheless, here we show that the Moon could constitute an invaluable reservoir of very ancient terrestrial rocks, stripped off the surface of our planet during the great bombardment that took place shortly after the origin of the solar system. These rocks could store information about the origin of life on Earth that our own planet wiped aeons ago.
SIXE (Spanish Italian X-ray Experiment) is an X-ray detector with geometric area of 2300 cm, form... more SIXE (Spanish Italian X-ray Experiment) is an X-ray detector with geometric area of 2300 cm, formed by four identical gas-filled Multicell Proportional Counters, and devoted to study the long term spectroscopy of selected X-ray sources in the energy range 350 keV. The main ...
We have computed and analyzed the evolution of primordial stars of ZAMS masses between 5 and with... more We have computed and analyzed the evolution of primordial stars of ZAMS masses between 5 and with and without overshooting, up to the early TP‐(S) AGB. The initial mass limits for the formation of carbon‐oxygen, oxygen‐neon degenerate cores and core‐collapse ...
The final stages of the evolution of electron--degenerate ONe cores, resulting from carbon burnin... more The final stages of the evolution of electron--degenerate ONe cores, resulting from carbon burning in ``heavy weight'' intermediate--mass stars ($8 M_{\sun}\la M \la 11 M_{\sun}$) and growing in mass, either from carbon burning in a shell or from accretion of matter in a close binary system, are examined in the light of their detailed chemical composition. In particular, we have modelled the evolution taking into account the abundances of the following minor nuclear species, which result from the previous evolutionary history: $^{12}$C, $^{23}$Na, $^{24}$Mg, and $^{25}$Mg. Both $^{23}$Na and $^{25}$Mg give rise to Urca processes, which are found to be unimportant for the final outcome of the evolution. $^{24}$Mg was formerly considered a major component of ONe cores (hence called ONeMg cores), but updated evolutionary calculations in this mass range have severely reduced its abundance. Nevertheless, we have parameterized it and we have found that the minimum amount of $^{24}$Mg required to produce NeO burning at moderate densities is $\sim 23%$, a value exceedingly high in the light of recent evolutionary models. Finally, we have determined that models with relatively small abundances of unburnt carbon ($X(^{12}$C)$\sim 0.015$) could be a channel to explosion at low to moderate density ($\sim 1\times 10^9$ g cm$^{-3}$). This is clearly below the current estimate for the explosion/collapse threshold and would have interesting consequences.
We compute and analyze the evolution of primordial stars of masses at the ZAMS between 5 M_sun an... more We compute and analyze the evolution of primordial stars of masses at the ZAMS between 5 M_sun and 10 M_sun, with and without overshooting. Our main goals are to determine the nature of the remnants of massive intermediate-mass primordial stars and to check the influence of overshooting in their evolution. Our calculations cover stellar evolution from the main sequence phase until the formation of the degenerate cores and the thermally pulsing phase. We have obtained the values for the limiting masses of Population III progenitor stars leading to carbon-oxygen and oxygen-neon compact cores. Moreover, we have also obtained the limiting mass for which isolated primordial stars would lead to core-collapse supernovae after the end of the main central burning phases. Considering a moderate amount of overshooting the mass thresholds at the ZAMS for the formation of carbon-oxygen and oxygen-neon degenerate cores shifts to smaller values by about 2 M_sun. As a by-product of our calculations, we have also obtained the structure and composition profiles of the resulting compact remnants. Opposite to what happens with solar metallicity objects, the final fate of primordial stars is not straightforward determined from the mass of the compact cores at the end of carbon burning. Instead, the small mass-loss rates typically associated to stellar winds of low metallicity stars might allow the growth of the resulting degenerate cores up to the Chandrasekhar mass, on time scales one or two orders of magnitude shorter than the time required to loose the envelope. This would lead to the formation of supernovae for initial masses as small as about 5 M_sun.
First Steps in the Origin of Life in the Universe, Jan 1, 2001
ABSTRACT The study of the origin of life on the Earth is impeded by the fact that very few ancien... more ABSTRACT The study of the origin of life on the Earth is impeded by the fact that very few ancient rocks from the era of the appearance of biological systems are preserved. The oldest sedimentary rock formations are about 3.9 billion years old, and even these show indications of the early emergence of life. Impacts, tectonic activity and erosion have hopelessly destroyed all the information predating the aforementioned age. Nevertheless, here we show that the Moon could constitute an invaluable reservoir of very ancient terrestrial rocks, stripped off the surface of our planet during the great bombardment that took place shortly after the origin of the solar system. These rocks could store information about the origin of life on Earth that our own planet wiped aeons ago.
SIXE (Spanish Italian X-ray Experiment) is an X-ray detector with geometric area of 2300 cm, form... more SIXE (Spanish Italian X-ray Experiment) is an X-ray detector with geometric area of 2300 cm, formed by four identical gas-filled Multicell Proportional Counters, and devoted to study the long term spectroscopy of selected X-ray sources in the energy range 350 keV. The main ...
We have computed and analyzed the evolution of primordial stars of ZAMS masses between 5 and with... more We have computed and analyzed the evolution of primordial stars of ZAMS masses between 5 and with and without overshooting, up to the early TP‐(S) AGB. The initial mass limits for the formation of carbon‐oxygen, oxygen‐neon degenerate cores and core‐collapse ...
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Papers by Jordi Gutiérrez