The evolution of massive stars and their spectra I. A non-rotating 60
  Msun star from the zero-age main sequence to the pre-supernova stage
  For the first time, the interior and spectroscopic evolution of a massive
star is analyzed from the zero-age main sequence (ZAMS) to the pre-supernova
(SN) stage. For this purpose, we combined stellar evolution models using the
Geneva code and atmospheric models using CMFGEN. With our approach, we were
able to produce observables, such as a synthetic high-resolution spectrum and
photometry, aiding the comparison between evolution models and observed data.
Here we analyze the evolution of a non-rotating 60 Msun star and its spectrum
throughout its lifetime. Interestingly, the star has a supergiant appearance
(luminosity class I) even at the ZAMS. We find the following evolutionary
sequence of spectral types: O3 I (at the ZAMS), O4 I (middle of the H-core
burning phase), B supergiant (BSG), B hypergiant (BHG), hot luminous blue
variable (LBV; end of H-core burning), cool LBV (H-shell burning through the
beginning of the He-core burning phase), rapid evolution through late WN and
early WN, early WC (middle of He-core burning), and WO (end of He-core burning
until core collapse). We find the following spectroscopic phase lifetimes:
3.22e6 yr for the O-type, 0.34e5 yr (BSG), 0.79e5 yr (BHG), 2.35e5 yr (LBV),
1.05e5 yr (WN), 2.57e4 yr (WC), and 3.80e4 yr (WO). Compared to previous
studies, we find a much longer (shorter) duration for the early WN (late WN)
phase, as well as a long-lived LBV phase. We show that LBVs arise naturally in
single-star evolution models at the end of the MS when the mass-loss rate
increases as a consequence of crossing the bistability limit. We discuss the
evolution of the spectra, magnitudes, colors, and ionizing flux across the
star's lifetime, and the way they are related to the evolution of the interior.
[abridged]
