Core - Halo Structure of Chemically Homogeneous Massive Star and Bending of Zero - Age Main - Sequence

We have recalculated interior structure of very massive stars of uniform chemical composition with the OPAL opacity. Very massive stars are found to develop a core-halo structure with an extended radiativeenvelope. With the core-halo structure, a more massive star has a more extended envelope, then the track of upper zero-age main-sequence (ZAMS) curves redward in the H-R diagram at > 100M (Z = 0:02), > 70M (Z = 0:05), and > 15M for helium ZAMS (X = 0:, Z=0.02). Therefore, e ective temperatures of very massive ZAMS stars are rather low: e.g., for the 200M star, log T e = 4:75 (Z = 0:004), 4.60 (Z = 0:02), 4.46 (Z = 0:05), and 4.32 (Z = 0:10). E ective temperatures of very luminous stars (> 120M ) found in the LMC, the SMC, and the Galaxy are discussed in relation with this metal dependence of curving upper main-sequence.