1. Mass Loss at the Tip of the AGB What do we know and what do we wish we knew!

2. Mechanism for dusty winds Poster: What happens when planets orbit in this dynamical atmosphere /wind

3. Dust enhances the mass loss and increases the momentum in the wind - but mass loss can occur without dust

4. Mass loss rate and metallicity Two factors separate high and low Z stars: 1.Low Z stars are smaller at the same L 2.Low Z stars don’t make dust Therefore lower Z stars survive to higher L (for a given M) 3 4 5 = logL

5. Characteristics of AGB mass loss Mass loss rates are very sensitive to stellar (and model) parameters => the main mass loss “event” is short-lived, lasting only about 200,000 years. AND the mass loss rate is subject to modulation - in time AND in space

6. Dependence of M on L and M Use the evolutionary track, R = a L b M -c Z -d  e, to eliminate R dependence. This works as long as the star stays “on track”. 3 4 5 logL Where M/M = L/L - an approximation to the “cliff” Power law fits: M=AL y M -z with 11<y<16, 15<z<20.

7. Steep mass loss law => lemming diagram: Stars evolve over a cliff -10 -8 -6 -4 log M = 0.7 1 1.4 2 2.8 4 core mass Chandrasekhar limit 0.6 0.4 0.2 0.0 -0.2 logM 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 logL the cliff

8. Stars near the cliff are Miras 0. 7 1 1. 4 2 2. 8 4 2.2 2.4 2.6 2.8 logP 5454354543 logL (Hipparcos distances to Miras are not very good - R ~ AU => angular diameter  parallax) Fit with NO parameter adjustment

9. Selection effects dominate empirical relations 7.06.86.66.46.26.05.85.6 -8 -7 -6 -5 -4 logLR/M log(Mdot) cliff stars with M/Sun indicated Reimers' formula 10xcliffM 0.1xcliff M 0.7 1.0 1.4 2.0 2.8 4.0 Fit with NO parameter adjustment

10. or fail to provide information on the dependence on mass Note: The uncertainty in P is very small => the spread in Mdot is large +/- 1 dex

11. Bowen models compared with VW relation: Note: The uncertainty in P is very small => the spread in Mdot is large Fit with NO parameter adjustment

12. Shell flashing modulates L, P, and Mdot

14. Peak to trough - 5 orders of magnitude!

15. Mira masses are near M i while the shaping occurs near M f -10 -8 -6 -4 log M = 0.7 1 1.4 2 2.8 4 core mass Chandrasekhar limit 0.6 0.4 0.2 0.0 -0.2 logM 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 logL OH-IR stars The shaping occurs near the dotted line

16. Sources of asphericity Angular momentum from a companion (star, planet)?  /  crit ~ 10 (M companion /M envelope ) (k/0.1) √(a/R * ) where I envelope = k M R * 2 and a = initial orbit of companion General magnetic field (?without rotation??) Global convection flow? Shell flashes with non-spherical symmetry? Note flash time scale << time scale of surface modulation of L Movies on the web: www.lcse.umn.edu and www.astro.uu.seåwww.lcse.umn.eduwww.astro.uu.seå M comp >0.1 M env (Porter & Woodward) (B. Freytag)

17. What do the products tell us? We expect that we should be able to learn something about the mass loss law from the distribution of stellar remnant masses and the M initial -M final relation. If we assume that L = c 1 (M core -c 2 ) and that the mass loss rate evolves with L according to Mdot = A L y M -z on a given evolutionary track, Then the curvature of Mi vs. Mf depends on (z+1)/y and the zero-point depends on A, c 1, c 2, and y. (project carried out by Agnes Kim)

18. Initial-final mass relation From Weidemann V., 2000, A&A, 363, 647 Evolution with mass loss and standard core mass - luminosity relations don’t fit. Mass loss pre- AGB tip or ?? There is a deeper problem

19. P=>L=>Mcore for Miras dn dlogP 200 400 600 days 0.56 0.60 0.64 0.72 0.85 Nearly all Miras have L such that we’d expect M core > 0.6 solar masses. 0.712 1.4 2.8

20. Their fate is to be white dwarf stars Nearly all WD have masses < 0.6 solar masses.

21. Paradox? OR: Core mass - L relation is wrong? Deep mixing can keep M core low while L increases. Miras are all in He flash peak? Unlikely given how common they are - life time of several times 10 5 years is not consistent with a reasonable number of shell flash peaks each lasting 1000 years. Only high mass stars (leaving higher mass WD) go through a Mira stage? Unlikely given the match in numbers and lifetimes and other constraints that all suggest the typical progenitor mass is not much more than 1 solar mass.

22. Conclusions Mass loss rates increase steeply with increasing L and decreasing M - exponents are 11-16 in L for fixed M and 15-20 for M at fixed L. Observed luminosities imply core masses > observed remnant masses so remnant masses do NOT provide a useful constraint on AGB mass loss (yet). The APN shaping event takes place when M ~ M remnant plus “a little”, but the mass loss process we understand is for Miras with M ~ initial AGB mass.

23. Spherical Planetary Nebula Abell 39 Credit & Copyright: George Jacoby (WIYN Obs.) et al., WIYN, AURA, NOAO, NSF.