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Fig. 1

image

Binding energy of the envelope, | Ebind | (lower panel), and its associated λ-value (upper panel), as a function of total stellar radius for two sets of models with Z = Z/ 50 (full lines, crosses) and Z = ZMW (dashed lines, squares). Independent of mass and metallicity, and before reaching the giant stages (R ≲ 1000R), the λ-values almost follow a power law with an exponent between −2/3 and −1 (upper and lower grey lines, respectively). The exceptions are stars with initial masses 60M at Z = ZMW (dashed blue line), which either become LBV stars, see Sect. 4.7, or have their envelopes stripped by enhanced wind-mass loss. The absolute binding energies of the 8M stars drop below the plotted range, down to approximately 2.7 × 1047erg and 7.3 × 1046erg for Z = Z/ 50 and Z = ZMW, respectively.

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