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 Characteristic OH maser emission (photo-dissoziation of H 2 O) Optically thick envelope typically intermediate mass stars

IRC Leao et al. 2006

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

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

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

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

Post-AGB objects van Winckel 2003

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

V605 Aql Hinkle et al. 2008

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

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 WDs Final He flash: born again scenario both scenarios not totally satisfying

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

Planetary Nebulae (PN)

Planetary nebulae Weinberger et al 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

Distances to PNe Hajan et al time diff. 5.5 yr

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!)

Abundances from post-AGB stars and PNe van Winckel 2003

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

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