The nucleosynthesis of 35Cl and 37Cl is different from each other as discussed in Chap. 1 . This results in different amounts of 35Cl and 37Cl produced in different stars as the evolution of stars can be vastly different. As a result, in stars and interstellar space the chlorine isotope ration can be significantly different from the ratio in the solar system. Because stable isotopes from individual elements opened a new window into the study of the details of stellar evolution, supernovae and galactic chemical evolution (Kobayashi et al. 2011) a significant number of studies have been published in which the different production rates of individual isotopes were estimated. Rauscher et al. (2002) made a very comprehensive study on the nucleosynthesis in stars with solar masses between 15 and 25. In principle production yields for 35Cl and 37Cl are in the same order of magnitude, and obtain 35Cl/37Cl production factors varying between 1.52 and 2.82, except for the model with solar mass 20, where production factor ratios are between 10.59 and 10.84. The discrepancies at solar mass 20, characterised by much higher yields of 35Cl as compared to 37Cl, are a consequence of the merging of the oxygen, neon, and carbon shells about a day prior to core collapse (Rauscher et al. 2002). Hoppe et al. (2023) showed that the model by Rauscher et al. (2002) provided good fits for the isotope compositions of many elements in presolar grains from SNe (e.g., Hoppe et al. 2010) and for the S-isotopic compositions of volatile species from 67P/Churyumov-Gerasimenko (Hoppe et al. 2018). Maas and Pilachowski (2018) summarised various other chlorine nucleosynthesis predictions (Kobayashi et al. 2006, 2011; Chieffi and Limongi 2013; Travaglio et al. 2004; Karakas and Lugaro 2016; Cristallo et al. 2015) In general, it appears that that the 37Cl yield is increasing (resulting in decreasing 35Cl/37Cl ratios) with increasing mass of the stars in which the isotopes are produced. Also the metallicity in a star can impact the 35Cl/37Cl production ratio. Maas and Pilachowski (2018) noticed that different published 35Cl/37Cl production ratios range from 1.20 to 4.23, compared to 3.13 for the observed solar system 35Cl/37Cl ratio (Lodders et al. 2009). 37Cl yields can increase in principle to extreme values in He-core masses and neutron excess (Prantzos et al. 1990). For example, in a 25 times solar mass star, 37Cl can be over-abundant by a factor of nearly 50 compared to the solar system 37Cl abundance (Pignatari et al. 2010). These resulting extremely low 35Cl/37Cl isotope ratios of ~0.06 have in practice not yet been observed in the universe.

Chlorine Isotope Ratios in Stars and Interstellar Space

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发表日期：

2025年

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Hans Eggenkamp

摘要

The nucleosynthesis of 35Cl and 37Cl is different from each other as discussed in Chap. 1 . This results in different amounts of 35Cl and 37Cl produced in different stars as the evolution of stars can be vastly different. As a result, in stars and interstellar space the chlorine isotope ration can be significantly different from the ratio in the solar system. Because stable isotopes from individual elements opened a new window into the study of the details of stellar evolution, supernovae and galactic chemical evolution (Kobayashi et al. 2011) a significant number of studies have been published in which the different production rates of individual isotopes were estimated. Rauscher et al. (2002) made a very comprehensive study on the nucleosynthesis in stars with solar masses between 15 and 25. In principle production yields for 35Cl and 37Cl are in the same order of magnitude, and obtain 35Cl/37Cl production factors varying between 1.52 and 2.82, except for the model with solar mass 20, where production factor ratios are between 10.59 and 10.84. The discrepancies at solar mass 20, characterised by much higher yields of 35Cl as compared to 37Cl, are a consequence of the merging of the oxygen, neon, and carbon shells about a day prior to core collapse (Rauscher et al. 2002). Hoppe et al. (2023) showed that the model by Rauscher et al. (2002) provided good fits for the isotope compositions of many elements in presolar grains from SNe (e.g., Hoppe et al. 2010) and for the S-isotopic compositions of volatile species from 67P/Churyumov-Gerasimenko (Hoppe et al. 2018). Maas and Pilachowski (2018) summarised various other chlorine nucleosynthesis predictions (Kobayashi et al. 2006, 2011; Chieffi and Limongi 2013; Travaglio et al. 2004; Karakas and Lugaro 2016; Cristallo et al. 2015) In general, it appears that that the 37Cl yield is increasing (resulting in decreasing 35Cl/37Cl ratios) with increasing mass of the stars in which the isotopes are produced. Also the metallicity in a star can impact the 35Cl/37Cl production ratio. Maas and Pilachowski (2018) noticed that different published 35Cl/37Cl production ratios range from 1.20 to 4.23, compared to 3.13 for the observed solar system 35Cl/37Cl ratio (Lodders et al. 2009). 37Cl yields can increase in principle to extreme values in He-core masses and neutron excess (Prantzos et al. 1990). For example, in a 25 times solar mass star, 37Cl can be over-abundant by a factor of nearly 50 compared to the solar system 37Cl abundance (Pignatari et al. 2010). These resulting extremely low 35Cl/37Cl isotope ratios of ~0.06 have in practice not yet been observed in the universe.