[Paper Review] 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

J. H. Groh, G. Meynet+2 more|arXiv (Cornell University)|Jan 28, 2014

Stellar, planetary, and galactic studies100 references79 citations

TL;DR

This study presents the first self-consistent modeling of a non-rotating 60 M⊙ massive star from the zero-age main sequence to the pre-supernova stage, combining stellar evolution models (Geneva code) with atmospheric/wind models (CMFGEN) to predict synthetic spectra, photometry, and ionizing flux. The key result is a significantly longer LBV phase (2.35×10⁵ yr) and revised spectroscopic phase lifetimes, with the star becoming undetectably faint in optical/IR filters near core collapse.

ABSTRACT

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]

Motivation & Objective

• To bridge the gap between theoretical stellar evolution models and observed massive star properties by computing synthetic observables.
• To investigate the spectroscopic evolution of a single, non-rotating 60 M⊙ star from ZAMS to core collapse.
• To quantify the lifetimes of key spectroscopic phases (O, LBV, WR, WO) and assess their dependence on mass loss and wind physics.
• To evaluate the detectability of massive star progenitors via photometric evolution and ionizing photon output.
• To clarify the physical origin of spectral type transitions in massive stars and their relation to internal evolutionary phases.

Proposed method

• Stellar evolution is modeled using the Geneva code, tracking internal structure and surface parameters from ZAMS to pre-SN.
• Atmospheric and wind structure are computed using the CMFGEN code, which models radiative transfer in non-LTE conditions.
• Synthetic high-resolution spectra and photometry are generated at multiple evolutionary phases to match observable quantities.
• Spectroscopic phase classification is based on observed spectral features (e.g., H, He, O lines) rather than chemical abundance or temperature thresholds.
• Mass-loss rates are computed using the Vink et al. (2001) recipe, which includes the bistability jump at ~21,000 K.
• Ionizing photon rates (Q0, Q1, Q2) are calculated from the synthetic spectra to assess ionizing output across evolution.

Experimental results

Research questions

• RQ1 How do the lifetimes of spectroscopic phases (O, LBV, WR, WO) evolve in a non-rotating 60 M⊙ star from ZAMS to core collapse?
• RQ2 What causes the formation of a long-lived LBV phase, and how is it related to the bistability limit in stellar winds?
• RQ3 How does the photometric evolution of the star affect its detectability in pre-explosion imaging surveys?
• RQ4 How do the ionizing photon outputs (Q0, Q1, Q2) change across the star's lifetime, and what drives their variations?
• RQ5 To what extent do synthetic spectra and photometry derived from combined evolution and atmosphere models improve the comparison with observations?

Key findings

• The O-type phase lasts 3.22×10¹ yr, with the star already showing supergiant (luminosity class I) characteristics at the ZAMS.
• The LBV phase lasts 2.35×10¹ yr, significantly longer than commonly assumed (a few 0.01 Myr), due to mass loss crossing the bistability limit at ~21,000 K.
• The WO phase is short-lived, lasting only 3.80×10¹ yr, but occurs at extremely high effective temperatures (>100,000 K) near core collapse.
• The star becomes progressively fainter in optical and near-IR filters during He-core burning, becoming undetectable with current surveys at the pre-SN stage.
• The duration of the WNL phase is reduced by a factor of ~20 compared to chemical abundance-based estimates, while the WNE phase duration is doubled.
• The ionizing photon rate Q0 remains roughly constant at 10¹¹¹.5 photons/s until the end of the main sequence, then increases during He-core burning and remains high until core collapse.