Stellar evolution with rotation

Abstract

Abstract.We examine the properties of Wolf-Rayet (WR) stars predicted by models of rotating stars taking account of the new mass loss rates for O-type stars and WR stars (Vink et al. 2000(Vink et al. , 2001Nugis & Lamers 2000) and of the wind anisotropies induced by rotation. We find that the rotation velocities v of WR stars are modest, i.e. about 50 km s −1 , not very dependent on the initial v and masses. For the most massive stars, the evolution of v is very strongly influenced by the values of the mass loss rates; below ∼12 M the evolution of rotation during the MS phase and later phases is dominated by the internal coupling. Massive stars with extreme rotation may skip the LBV phase. Models having a typical v for the O-type stars have WR lifetimes on the average two times longer than for non-rotating models. The increase of the WR lifetimes is mainly due to that of the H-rich eWNL phase. Rotation allows a transition WN/WC phase to be present for initial masses lower than 60 M . The durations of the other WR subphases are less affected by rotation. The mass threshold for forming WR stars is lowered from 37 to 22 M for typical rotation. The comparisons of the predicted number ratios WR/O, WN/WC and of the number of transition WN/WC stars show very good agreement with models with rotation, while this is not the case for models with the present-day mass loss rates and no rotation. As to the chemical abundances in WR stars, rotation brings only very small changes for WN stars, since they have equilibrium CNO values. However, WC stars with rotation have on average lower C/He and O/He ratios. The luminosity distribution of WC stars is also influenced by rotation.

OB Associations, Wolf–Rayet Stars, and the Origin of Galactic Cosmic Rays

“…Although the details of the Cassé & Paul calculations are not included in that paper, the 2% that they quote is material ejected only in the WC phase. In both the Higdon & Lingenfelter (2003) and the Meynet & Maeder (2003 models, the ~20% of material includes all material ejected from the birth of the star to the end of the WC phase. Additionally, Cassé & Paul used the solar energetic particle ratio of 0.13 (Mewaldt, et al 1979) instead of the solar wind value of 0.073 (Geiss, 1973) Another important constraint for the origin of cosmic rays, previously obtained from CRIS results, is the requirement that nuclei synthesized and accelerated by SNe are accelerated at least 10 5 yr after synthesis.…”

“…(For details of these models of rotating stars, see Meynet & Maeder, 2003 for the associated nucleosynthesis see Arnould et al 2006.) The end of the WR phase of each star is followed by core collapse.…”

New type of brightness variations of the colliding wind WO4 + O5((f)) binary WR 30a

“…In massive WCE and WO stars, carbon and oxygen are produced continuously in the non-degenerate He-burning core and are exposed by mass loss stripping (Maeder 1991;Meynet & Maeder 2003). WO stars have number abundance ratios (C+O)/He 0.62 (Kingsburgh et al 1995), initial masses M i > 40 M and WO-lifetimes of 27 000 yr to 62 000 yr, depending on initial mass and rotation on the main sequence (Meynet 2003, private communication).…”

“…The classification of the WR star of WR 30a had been taken to be WC4 by Lundström & Stenholm (1984b), and later WO4 by Smith et al (1990a,b) and Crowther et al (1998) companion star has been classified as O4 (Moffat & Seggewiss 1984). Niemela (1995) reported the first radial velocity study for WR 30a, and suggested that WR 30a might be a short period binary.…”

Investigation of Cyg OB2 #11(O5 Ifc) by Modelling its Atmosphere

“…Maeder et al (2009) write that N/C ratio is sensitive to many parameters such as the age of the star, metallicity, rotation velocity, magnetic field. Evolutionary tracks computed in 2013 are below the tracks designed in 2003 for the same stellar masses (Meynet & Maeder 2003). Cyg OB2 #11 is located above the evolutionary tracks.…”