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AGB mass-loss and recycling

T. Le Bertre, E. Gérard Paris Observatory and J. M. Winters IRAM. AGB mass-loss and recycling. The Dusty and Molecular Universe, Paris, 27-29 October 2004. AGB outflows. Slow winds : V exp ~ few to 20 km s -1 Massive winds :

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AGB mass-loss and recycling

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  1. T. Le Bertre, E. Gérard Paris Observatory and J. M. Winters IRAM AGB mass-loss and recycling The Dusty and Molecular Universe, Paris, 27-29 October 2004

  2. AGB outflows Slow winds : Vexp~ few to 20 km s-1 Massive winds : Mdot~ 10-8 to a few 10-4 Msol yr-1 AGB stars are therefore surrounded by expanding circumstellar shells that can be traced through their emission from dust and gas in the infrared and radio domains.

  3. through mass loss they contribute to the replenishment of the ISM • they also contribute to the chemical evolution of the ISM, in particular to its enrichment in carbon + Mass loss affects the star evolution (luminosity, nucleosynthesis) ----> role of stellar mass loss in galactic evolution (in particular as compared to infall)

  4. Sedlmayr (1994, IAU coll. 146, 163) but dependence with galactic location and with time + galactic infall

  5. The outflows on the AGB are variable on timescales that may be short compared to stellar evolution IRC +10216 (Mauron & Huggins 2000, A&A 359, 707) • CO rotational transitions from J=2-1 to J=7-6 indicate mass loss variations on the same timescales (Kemper et al. 2003, A&A 407, 609) • Mass loss variations may be so large that one observes a “detached shell” (e.g. Olofsson et al. 2000, A&A 353, 583)

  6. TT Cyg (Olofsson et al. 2000, A&A 353, 583)CO 1-0Vlsr +/- 2 km/s Mdot (in.) ~ 3 10-8 Msol yr-1 Mdot (out.) ~ a few 10-5 Msol yr-1 ---> meaning of Mdot ? We may have large differences on the estimates of Mdot when we use different tracers sensitive to different zones of the circumstellar shells (in addition to the abundance problem)

  7. ---> necessity to combine these different tracers • Need to understand better the mass loss process and its history • Molecular lines are useful in particular because of the high spectral resolution available with heterodyne techniques, but they probe a limited extent of the circumstellar shells. • The dust emission at long wavelengths may help to trace the circumstellar shells on large distances, but cannot provide velocity information. Izumiura et al. 1996, A&A 315, L221 ISOPHOT 90 µm

  8. A special mention may be done to the atomic line of hydrogen at 21 cm that up to now has not been much used. • optically thin in most situations •  = 1.4 GHz ==> h/kT << 1 ==> TB  NH • circumstellar HI should be protected by the surrounding ISM • ~70 % of mass in hydrogen Glassgold & Huggins (1983, MNRAS 203, 517): if Teff > 2500 K, all hydrogen should be atomic if Teff < 2500 K, H2 should bephotodissociated at ~ 1017 cm (lines at 28 µm….)

  9. EP Aqr (Winters et al. 2003, A&A 409, 715) Le Bertre & Gérard 2004, A&A 419, 549 Complementarity between H I and CO : same multiple components, but the relative intensities are different (the zones which are probed are distinct)

  10. EP Aqr (Le Bertre & Gérard 2004, A&A 419, 549) 4’ x 22’ or 0.16pc x 0.86pc (at 135 pc) Complex spatial and dynamic structures The HI emission is very extended (~ 1 pc) Mtot ~ 0.07 Msol

  11. EP Aqr Winters et al. 2003, A&A 409, 715 CO : Vlsr = -34 km s-1 Le Bertre & Gérard 2004, A&A 419, 549 HI : Vlsr = -31 km s-1 Gonzalez Delgado et al. 2003, A&A 411, 123 SiO : Vlsr = -32 km s-1 (thermal SiO, v=0, J=2-1) ==> need to resolve spatially these emissions with a spectral resolution corresponding to 1 km s-1,or better

  12. Y CVn (Le Bertre & Gérard 2004, A&A 419, 549) Knapp et al. 1998, ApJS 117, 209 H I can be traced out to the ISM (Mtot ~ 0.06 Msol) Izumiura et al. 1996, A&A 315, L221 ---> (ISOPHOT 90 µm : 12x8 arcmin2)

  13. The matter in the shell is the sum of slowed down circumstellar material and accelerated external (ISM ?) material from Chevalier & Tiret (2004) ==> need to separate the 2 phases spectroscopy ? dust properties ? high spatial resolution over a large f.o.v.

  14. Other difficulties • non-sphericity bipolar flows, e.g. X Her (Kahane & Jura 1996) V Hya (Sahai et al. 2003) clumpiness, e.g. Mira (Lopez et al. 1997) IRC+10216 (Weigelt et al. 2002) ----> clumpiness might be an effect of the self-amplifying nature of the dust formation process (Woitke, this conference) ===> importance imaging with high spatial resolution • distance -in general, mass loss rate estimates depend on the adopted distance -needed to locate the sources in the Galaxy ===> importance of GAIA

  15. A further complication The atmospheric composition of AGB stars depends on initial mass, initial abundances, multiplicity, … , and changes as a function of time. Standard dichotomy : C/O < 1 ---> O-rich, silicate grains, …. C/O > 1 ---> C-rich, carbon grains, …. ==> the composition of the gas and grains injected into the ISM is variable

  16. Dependence of the nature of the presently injected material on galacto-centric distance Thin line : M+C AGB starsThick line : C only IRTS data(Le Bertre et al. 2003, A&A 403, 943) IR surveys should be useful to evaluate this effect in different locations of the Galaxy

  17. Summary • CO, HI, SiO, …, radio lines and dust emission are complementary probes of the expanding circumstellar shells and of the zone where they interact with the ISM. • Infrared surveys are useful to evaluate the contribution of the population of AGB stars to the replenishment of the ISM.

  18. Simulations of the HI emission from a spherical source Unresolved source with V = const. Resolved source with V = const.

  19. Unresolved source with decreasing V Resolved source with decreasing V

  20. Y CVn (Le Bertre & Gérard 2004, A&A 419, 549)

  21. Woitke (this conference)

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