stellar evolution with rotation
DESCRIPTION
Stellar evolution with rotation. Wolf-Rayet stars at solar metallicity. WR Nebula WR124, taken with HST. Tim van Werkhoven. Wolf-Rayet stars Evolution of rotational speed Evolution in H-R diagram Evolution of mass Comparison of (non)-rotational models WR-subphases - PowerPoint PPT PresentationTRANSCRIPT
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