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Post-AGB evolution

Post-AGB evolution. Learning outcome. evolution from the tip of the AGB to the WD stage object types along the post-AGB evolution basics about planetary nebulae basics about white dwarfs. OH/IR stars. O-rich stars at the tip of the AGB Maximum of SED at 10µm

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Post-AGB evolution

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  1. Post-AGB evolution

  2. Learning outcome • evolution from the tip of the AGB to the WD stage • object types along the post-AGB evolution • basics about planetary nebulae • basics about white dwarfs

  3. OH/IR stars • O-rich stars at the tip of the AGB • Maximum of SED at 10µm • Characteristic OH maser emission(photo-dissoziation of H2O) • Optically thick envelope • typically intermediatemass stars

  4. IRC+10216 Leao et al. 2006

  5. The end of the AGB phase • Mass loss removes most of the envelope • H-burning shell finally reaches the surface • This leads to an increase in temperature,the star moves to the left in the HRD • Luminosity and timescale depend on core mass

  6. Post AGB-evolution Blöcker 1995 time steps in units of 10³ yrs

  7. Post-AGB objects RV Tau / SRds supergiants of spectral type F-K circumstellar shell depletion of elements into dust Giridhar et al. 1999

  8. Post-AGB objects Protoplanetary Nebulae (PPN) not clearly defined (resolved objects?) star typically visible only inscattered light e.g. Red Rectangle Osterbart et al. 1997

  9. Post-AGB objects van Winckel 2003

  10. Final Flash / Born Again AGB Stars • star leaves AGB shortly before a TP • final TP occurs already on the way to the WD stage • Star returns to AGB within a very short time • single or double loop scenario

  11. V605 Aql Hinkle et al. 2008

  12. FG Sge • central star of PN He1-5 • Real-time stellar evolution • C-star since 1981 • 1992 ejection of a dust shell van Genderen 1994

  13. R CrB stars • only ~ 50 objects known in the Milky Way • hydrogen deficient G-K supergiant exhibiting erratic variabilities • infrared excess • 2 scenarios:Double degenerate: fusion of two WDsFinal He flash: born again scenarioboth scenarios not totally satisfying

  14. R CrB stars Clayton 1996 result of ejection of a dust shell

  15. Planetary Nebulae (PN)

  16. Planetary nebulae Circumstellar material ejected during the AGB phase ionized by the central star. Spectrum characterized by emission lines of H and [O III] detectable at large distances Weinberger et al. 1994

  17. Distances to PNe time diff. 5.5 yr Hajan et al. 1993

  18. Abundances from post-AGB stars and PNe • allow insight in abundances returned to ISM • in several objects s-process elements enhanced (dredge up) • effect of depletion: elements selectively removed by dust formation ([Zn/Fe]=+3.1!)

  19. Abundances from post-AGB stars and PNe van Winckel 2003

  20. White dwarfs • Better: degenerated dwarfs • Upper mass limit 1.44 Msun (nonrotating), but typically significantly lower (0.6 Msun) • High log g and P values at the surface, thus highly broadened lines • Cooling not totally understood, important for age determination

  21. Types of White Dwarfs • DC: barely lines • DO: He II lines dominate • DB: He I strong, no H • DA: H present, no He • Surface composition influenced by diffusion (radiation pressure, gravity) and accretion of ISM

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