标题： 它们比我们认为的更老吗？预主序星 显示英文标题

标题： Are pre-MS stars older than we thought?

摘要： 我们给出了根据恒星通过其前主序阶段的收缩确定的年轻星团和星群的一致年龄排序。 我们将这些与从上主序星演化得出的年龄进行比较，发现上主序星的年龄比前者老 1.5 到 2 倍。 我们表明，相比于主序星的其余部分，增加 O 星中的双星比例以及等质量双星的数量无法消除这一差异。 显示英文摘要

摘要： We present a consistent age ordering for young clusters and groups determined using the contraction of stars through their pre-main-sequence phase. We compare these with ages derived from the evolution of the upper main-sequence stars, and find the upper MS ages are older by a factor 1.5 to 2. We show that increasing the binary fraction and number of equal-mass binaries amongst the O-stars compared to the rest of the MS cannot remove this discrepancy.