arXiv subjects

R. Hirschi

Publications and source records attributed to R. Hirschi.

75 records · Page 5Linked to original sources

arXiv2004

Yields of rotating stars at solar metallicity

We present a new set of stellar yields obtained from rotating stellar models at solar metallicity covering the massive star range (12-60 solar masses). The stellar models were calculated with the latest version of the Geneva stellar evolution code described in Hirschi et al (2004). Evolution and nucleosynthesis are in general followed up to silicon burning. The yields of our non-rotating models are consistent with other calculations and differences can be understood in the light of the treatment of convection and the rate used for C12(a,g)O16. This verifies the accuracy of our calculations and gives a safe basis for studying the effects of rotation on the yields. The contributions from stellar winds and supernova explosions to the stellar yields are presented separately. We then add the two contributions to compute the total stellar yields. Below about 30 solar masses, rotation increases the total metal yields, Z, and in particular the yields of carbon and oxygen by a factor of 1.5-2.5. As a rule of thumb, the yields of a rotating 20 solar masses star are similar to the yields of a non-rotating 30 solar masses star, at least for the light elements considered in this work. For very massive stars (around 60 solar masses), rotation increases the yield of helium but does not significantly affect the yields of heavy elements.

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arXiv2004

Rotating massive stars: Pre-SN models and stellar yields at solar metallicity

We present a new set of stellar yields obtained from rotating stellar models at solar metallicity covering the massive star range (9-120 solar masses). The stellar models were calculated with the latest version of the Geneva stellar evolution code described in Hirschi et al 2004a. The contributions from stellar winds and from supernova explosions to the stellar yields were calculated separately. The two contributions were then added to compute the total stellar yields (Hirschi et al 2004b). The effects of rotation on pre-supernova models are significant between 15 and 30 solar masses. Above 20 solar masses, rotation may change the radius or colour of the supernova progenitors (blue instead of red supergiant) and the supernova type (IIb or Ib instead of II). Rotation increases the helium and CO core sizes by a factor about 1.5. Thus, rotation increases the total metallic yields and in particular the yields for carbon and oxygen by a factor 1.5-2.5. For Wolf-Rayet stars (M>30 solar masses), rotation increases the yields of helium and other hydrogen burning products but does not significantly affect the yields of heavy elements.

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arXiv2004

Stellar evolution with rotation XII: Pre-supernova models

We describe the latest developments of the Geneva stellar evolution code in order to model the pre-supernova evolution of rotating massive stars. Rotating and non-rotating stellar models at solar metallicity with masses equal to 12, 15, 20, 25, 40 and 60 solar masses were computed from the ZAMS until the end of the core silicon burning phase. We took into account meridional circulation, secular shear instabilities, horizontal turbulence and dynamical shear instabilities. Most of the differences between the pre-supernova structures obtained from rotating and non-rotating stellar models have their origin in the effects of rotation during the core hydrogen and helium burning phases. The effects of rotation on pre-supernova models are significant between 15 and 30 solar masses. Indeed, rotation increases the core sizes (and the yields) by a factor ~ 1.5. Above 20 solar masses, rotation may change the colour of the supernova progenitors (blue instead of red supergiant) and the supernova type (Ib instead of II). Rotation affects the lower mass limits for radiative core carbon burning, for iron core collapse and for black hole formation. For Wolf-Rayet stars (M > 30 solar masses), the pre-supernova structures are mostly affected by the intensities of the stellar winds and less by rotational mixing. Finally, the core of our rotating WR stars contain enough angular momentum to produce GRBs.

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