2 Life cycle of a massive star

In the "Conti scenario'', the evolution of a massive star is determined by the amount of mass loss it undergoes (Conti 1976; Maeder & Conti 1994). This mass loss is driven by the combination of the star's intrinsic luminosity and opacity due to metal lines. The more luminous a star is, the greater the outward force, and the more metals present in the wind, the greater the opacity and hence the ability to drive a mass-losing stellar wind. Our picture of massive stellar evolution is rapidly changing, as new models including rotation are developed (Maeder & Meynet 2000; Meynet & Maeder 2000). It now appears that rotation is second only to mass loss rate in its effect on massive stellar evolution, and it may even be more important at low metallicities (Maeder & Meynet 2001).

The current qualitative overview of massive stellar evolution is as follows. For a star with an initial mass of $\ge$30 $M_{\odot}$, mass loss and mixing on the main sequence deplete the hydrogen-rich envelope and reveal the equilibrium products of CNO-cycle hydrogen burning, creating a WN star. Additional mass loss and mixing reveals the products of He-burning, and the star becomes a WC star. The star will end its life as a Type Ib or Ic supernova. This evolution may or may not be punctuated by eruptions and episodes of large mass loss where the star is identified as an LBV.

 

Table 1: Filter description.

Central $\lambda$ ($\mu$m)	FWHM ($\mu$m)
2.032	0.010
2.062	0.010
2.077	0.015
2.142	0.020
2.161	0.022
2.191	0.013
2.248	0.024