标题： 放射性元素在LMC中的演化：对未来伽马射线调查的预测 显示英文标题

标题： Evolution of radioactive elements in the LMC: predictions for future gamma-ray surveys

摘要： 短寿命放射性核素，如26Al和60Fe，是恒星形成的示踪剂。因此，它们的丰度可以揭示宿主星系的近期恒星形成历史。考虑到未来的伽马射线调查，我们使用新的化学演化模型预测了大麦哲伦星云（LMC）中这两种元素的质量和通量。我们最好的模型再现了LMC中alpha/Fe比值的丰度模式、气体质量、平均金属丰度、当前时间超新星和新星的速率。我们展示了三个主要结果：i）LMC的最佳模型表明，最初恒星形成率非常平缓，最近有一次爆发，并且初始质量函数类似Salpeter型。ii）26Al的预测质量为0.33 M_Sun，其中2/3由大质量恒星产生，1/3由新星产生。iii）60Fe的预测质量为0.44 M_Sun，全部由大质量恒星产生。这一结果表明60Fe的比例更大，与银河系不同。这种差异的原因在于所采用的初始质量函数，即LMC的初始质量函数包含比银河系更多的大质量恒星。这些预测对计划于2027年发射的COSI-SMEX任务可能有帮助。预计26Al的1.809 MeV谱线和60Fe的1.173和1.332 MeV谱线的伽马射线线通量分别在(0.2-2.7)x10^-6 ph cm^-2 s^-1和(0.7-2.8)x10^-7 ph cm^-2 s^-1范围内。这种新仪器可能具有灵敏度，在其规定的两年任务期内检测到预测的1.8 MeV通量的上限。 显示英文摘要

摘要： Short-lived radionuclides, such as 26Al and 60Fe, are tracers of star formation. Therefore, their abundances can unravel the recent star formation history of the host galaxy. In view of future gamma-ray surveys, we predict the masses and fluxes of these two elements in the Large Magellanic Cloud (LMC) using new chemical evolution models. Our best model reproduces the abundance patterns of alpha/Fe ratios, the gas mass, the average metallicity, the present time supernova and nova rates observed in LMC. We show three main results: i) the best model for the LMC suggests a star formation rate very mild at the beginning with a recent burst, and a Salpeter-like initial mass function. ii) The predicted mass of 26Al is 0.33 M_Sun, 2/3 produced by massive stars and 1/3 by novae. iii) The predicted mass of 60Fe is 0.44 M_Sun, entirely produced by massive stars. This result suggests a larger fraction of 60Fe, at variance with the Milky Way. The explanation for this lies in the adopted initial mass function, that for the LMC contains more massive stars than for the Milky Way. These predictions can be useful for the COSI-SMEX mission planned for launch in 2027. The expected gamma-ray line fluxes for the 1.809 MeV line of 26Al and the 1.173 and 1.332 MeV lines of 60Fe are in the range of (0.2-2.7)x10^-6 ph cm^-2 s^-1 and (0.7-2.8)x10^-7 ph cm^-2 s^-1, respectively. This new instrument could have the sensitivity to detect the upper end of the predicted 1.8 MeV flux within its nominal two-year mission.