The evolution of massive stars

Abstract

The evolution of stars with masses between 15M0 and 100M0 is considered. Stars in this mass range lose a considerable fraction of their matter during their evolution.The treatment of convection, semi-convection and the influence of mass loss by stellar winds at different evolutionary phases are analysed as well as the adopted opacities.Evolutionary sequences computed by various groups are examined and compared with observations, and the advanced evolution of a 15Mo and a 25M0 star from zero-age main sequence (ZAMS) through iron collapse is discussed.The effect of centrifugal forces on stellar wind mass loss and the influence of rotation on eyolutionary models is examined. As a consequence of the outflow of matter deeper layers show up and when the mass loss rates are large enough layers with changed composition, due to interior nuclear reactions, appear on the surface.The evolution of massive close binaries as well during the phase of mass loss by stellar wind as during the mass exchange and mass loss phase due to Roche lobe overflow is treated in detail, and the value of the parameters governing mass and angular momentum losses are discussed.The problem of the Wolf-Rayet stars, their origin and the pq~sibilities of their' production either as single stars or as massi:ce binaries is examined.Finally, the origin of X-ray binaries is discussed and the scenario for the formation of these objects (starting from massive ZAMS close binaries, through Wolf-Rayet binaries leading to OB-stars with a compact companion after a supernova explosion) is reviewed and completed, including stellar wind mass loss.

Gamma rays from active regions in the galaxy: The possible contribution of stellar winds

“…Data gathered at various wavelengths (mainly in the UV and radio ranges) have shown that massive O and B stars (M > 20 Mo) shed a considerable amount of mass in the form of stellar winds (e.g., de Loore, 1980). The mass-loss from O stars is on the order of 10 -7 M o yr-l, Of stars reaching 10 -6 M o yr-1.…”

“…They are thought to be a late, but comparatively brief (a few 105 yr, e.g., Maeder and Lequeux, 1982) evolutionary stage of O stars, perhaps immediately preceded by an Of phase (Conti et al, 1979). Several models exist for this transition (Maeder, 1982;de Loore, 1980), but it is thought that all O stars above ~ 23 M o display the 'WR phenomenon' before becoming supernovae (Maeder and Lequeux, 1982). However, the WR stars appear to be linked somewhat less frequently than O stars with OB associations (or giant H II regions as their tracers), since at least ~ 60~o are isolated objects (Vand der Hucht et al, 1981).…”

Mass loss and evolution of massive stars

“…Therefore the amount and mode of mass loss in early (blue) phases will significantly affect all subsequent evolution, whereas the amount and mode of mass loss as intermediate to late ty_ pe stars, may control the reappearance of the models as blue evolved objects. The recent reviews by de Loore (1979Loore ( , 1980 on the evolution of massive stars undergoing mass loss by stellar wind during core and shell H-burning phases make superflous here a deta_i_ led description of those results. Therefore we will be onlyconcerned with the most recent advancements, yet the main re suits on the subject will be also outlined.…”

“…As is well known, the mass exchange, and more recently a combination of mass exchange and mass loss by stellar wind, offers an easy and straightforward scenario for the production of WR stars in binary systems. The situation has been recently reviewed by de Loore (1979Loore ( , 1980. On the contrary, the possibility that mass loss by stellar wind may transform a single 0 type star into a WR star, as suggested some time ago by Conti (1976a), is still an unsettled question.…”

Evolution of rotating binary stars

“…The conventional theories for the evolution of close binaries usually assume that the synchronism of the rotation with the orbital motion is always reached (Kippenhahn & Weigert 1967;De Loore 1980;Huang & Taam 1990;Vanbeveren 1991;De Greve 1993). The potential for a synchronous rotating component in a Roche model is given by…”