主序前星密的星际物质构成的包层环绕。在结束原恒星阶段后,恒星继续收缩,直至内部氢元素开始燃烧,此时结束主序前星阶段,进入零龄主序(英语:Zero age main sequence )。 這些天體的能量來自於引力收縮(相對於主序星的氫融合)。在赫羅圖,主序帶前階段,質量在0
NGC 67091086/300716. Cole-Kodikara, Elizabeth M.; et al. NGC 6709: A Faint Zero -Age Main Sequence Open Cluster. The 20.5th Cambridge Workshop on Cool Stars, Stellar
WR 102 stars and their spectra I. A non-rotating 60 Msun star from the zero -age main sequence to the pre-supernova stage. Astronomy & Astrophysics. 2014, 564:
高光度藍變星stars and their spectra I. A non-rotating 60 Msun star from the zero -age main sequence to the pre-supernova stage. Astronomy & Astrophysics. 2014, 564:
紅巨星分支young open clusters. III – Empirical isochronous curves and the zero age main sequence . Astronomy and Astrophysics. 1981, 97: 235. Bibcode:1981A&A....97