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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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.
+ Mass loss affects the star evolution
----> role of stellar mass loss in galactic evolution
(in particular as compared to infall)
but dependence with galactic location and with time
+ galactic infall
(Mauron & Huggins 2000, A&A 359, 707)
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)
Izumiura et al. 1996, A&A 315, L221
ISOPHOT 90 µm
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….)
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)
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
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
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)
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
-in general, mass loss rate estimates depend on the adopted distance
-needed to locate the sources in the Galaxy
===> importance of GAIA
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
Unresolved source with V = const.
Resolved source with V = const.
Resolved source with decreasing V