upper main sequence

例句：

1. 1. The star is located in theupper main sequence.
   这颗星位于上部主序星。
2. 2. The upper main sequence is aregion of space where stars are born anddie.
   上部主序星是一个恒星诞生和消亡的区域。
3. 3. Astronomers study theupper main sequence to understand how stars evolve.
   天文学家研究上部主序星，以了解恒星是如何演化的。