Stellar evolution with rotation

Tim van Werkhoven

Wolf-Rayet stars at solar metallicity

WR Nebula WR124, taken with HST

• Wolf-Rayet stars• Evolution of rotational speed• Evolution in H-R diagram• Evolution of mass• Comparison of (non)-rotational models• WR-subphases• Comparison with observation• Conclusion

Stellar evolution with rotation

Tim van Werkhoven

• Massive, ~ 20 Msun

• Mass loss ~ 10-6-10-5 Msun/y (compare 10-14 Msun/y)

• Hot, ~50,000 K• Luminous, ~105-106 Lsun

• Extremely rare because of short life• Different types, WC, WN and WO

• (Carbon, Nitrogen, Oxygen line-features)• WR stars believed to be at the end of their lives

• Progenitors of supernovae and γ-ray bursts

Stellar evolution: Wolf-Rayet stars

Tim van Werkhoven

Stellar evolution: Rotational speed

Tim van WerkhovenRotational speed evolution tracks for different stars

Stellar evolution: Rotational speed

Tim van WerkhovenΩ/Ω-critical-evolution tracks for different stars

Stellar evolution: Rotational speed

Tim van Werkhoven

• Steep drops: end of MS (bi-stability limit)• Dependent on initial mass

• Higher masses lose more angular momentum (more wind)

Stellar evolution: Rotational speed

Tim van WerkhovenEvolution for 85 and 25 Msun stars

Left (85 Msun):

• Mass loss, Ω, R, v• 25Msun, H-burning stops

• R,Ω,P,v~

Right (25 Msun)

• P, because T, R• At the end, v because

you see deeper layers

Stellar evolution: H-R Diagram

Tim van Werkhoven

Evolution in the H-R diagram

Stellar evolution: H-R Diagram

Tim van WerkhovenEvolution in the H-R diagram for a 120 Msun star

• More luminous• M<30Msun, bandwidth is enlarged (larger He-core)• M>50Msun, bandwidth is reduced (surface He

enhancement leads to bluer track)• If no rotation is taken into account, masses are

over-estimated• Possible result of mass-discrepancy (Herrero et al. 2000)

For 120 Msun• Wider range in L

Stellar evolution: H-R Diagram

Tim van Werkhoven

Stellar evolution: Mass change

Tim van WerkhovenInitial versus final mass for different models

• In general: lower final mass• For M~55 Msun, rotation does not matter

• Caused by different evolutionary tracks• Corresponds well to observations

• Average mass for WC stars 12 ± 3 Msun (6 star avg.)

• Higher masses than the older model• Possible result of mass-discrepancy (Herrero et al. 2000)

Stellar evolution: Mass change

Tim van Werkhoven

Stellar evolution: Comparison

Tim van WerkhovenEvolution models for a 60 Msun star

Comparison:• Same L when entering

WR-phase -> same mass! (different evolution)

• No rotation -> LBV phase

• No rotation -> lower mass WR-phase

Stellar evolution: WR-subphases

Tim van Werkhoven

WR-subphases

• eWNL phase mainly affected• Transitional phase introduced, H+He burning (right)• Minimum mass is lowered by rotation• Dependent on Z

Stellar evolution: Observation

Tim van Werkhoven

Comparison with observational results

Stellar evolution: Observation

Tim van Werkhoven

Comparison with observational results

• Rotation of stars improves models• Rotation is a key ingredient for stellar evolution• Opens new ways to interesting questions

• γ-ray bursts• Supernovea• Ring nebulae• Pulsar rotation

Stellar evolution: Conclusion

Tim van Werkhoven

• Meynet, G. & Maeder, A., 2003, A&A 404, p. 975-990

• Meynet, G. & Maeder, A., 2000, A&A 361, p. 101-120

Stellar evolution: References

Tim van Werkhoven