Setting the Stage. We All know why galaxies care about AGB Stars:

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Rebecca Terry
5 years ago
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1 Setting the Stage We All know why galaxies care about AGB Stars: AGB Energetic role in Stellar Populations (SED) Chemical Yields (He, Li, C, N, O, Ne, Na, Mg, Al, s-p) Dust production (Carbonaceous and silicate grains) Establish the initial-mass-final -mass relation, hence the mass return by dying stars in galaxies Alvio Renzini, III Congress of Vienna on Why Galaxies Care about AGB Stars, July 28, 2014

2 The Three Macrophysics Drivers of AGB Evolution Envelope Convection Mass Loss rd Mixing (3 Dredge up) Neglecting higher order complexities (e.g., rotation, magnetic fields,...) In practice, the above processes are parametrized, e.g., Mixing length theory for convection, simple wind mass loss rates formulae + envelope ejection, heuristic mixing algorithms.

3 The Three Macrophysics Drivers of AGB Evolution* i.e., why modeling AGB evolution is especially troublesome Envelope Convection (e.g., via the Mixing Length) Controls Radius and HBB Radius controls Mass Loss HBB controls Luminosity Luminosity controls Mass Loss Radius controls TDU Summary: Envelope Convection controls Mass Loss and TDU * Best applicable to stars with HBB (M>~2.5-3 M )

4 The Three Macrophysics Drivers of AGB Evolution Third Dredge-up ( = MDredge/ MH) Controls: Surface composition Rate of Core Mass Increase Core Mass controls luminosity Luminosity controls Mass Loss Surface composition controls Radius Radius controls TDU and Mass Loss Surface composition controls Mass Loss Summary: TDU controls Mass Loss, HBB & TDU

5 The Three Macrophysics Drivers of AGB Evolution Mass Loss (AGB wind + Superwind ) Controls: * Radius * Luminosity * TDU * the end of AGB phase Summary: Mass Loss controls HBB & TDU

6 The three processes are not separable: each of them affects the others A double circulation of connections... Mass Loss HBB Convection TDU Just one example, the TDU

7 Longer AGB lifetime Small TDU Assumptions Control Luminosity Evolution large core mass increase hence Mass Loss and AGB largetermination luminosity increase Depending on specific models, may be ~0 or ~1 (!!!) dramatic mass loss prompt abortion of AGB Karakas, Lattanzio & Pols 2002 phase (especially for HBB) Ventura & D'Antona 2009 much different element yields in the 2 cases!!

8 The Three Macrophysics Drivers of AGB Evolution are tightly interlaced to each other!!! This implies that one cannot calibrate each free parameter independently of the others... and therefore simple analytical formulations to construct synthetic AGB evolution sequences are bound to miss most of these intricate connections Summary: Only a tiny fraction of the AGB parameter space has been explored so far: AGB evolution is a particularly nasty puzzle!

9 Globular Clusters: A New Frontier for the AGB and a new Opportunity to Understand it Multiple stellar generations are ubiquitous among Globular Clusters Possibly/Likely built out of virtually pure AGB ejecta!

10 NGC 2808: at least 3 main sequences with the same metallicity: hence with different helium content: Second (third) generation stars are made of material 8 Exposed to high temperature (~10 K) p-captures Piotto+2007 Carretta+2009

11 New WFC3/UVIS data with UV Milone et al. In preparation

12 The unanticipated complexity of NGC 2808 Milone et al. In preparation At least seven distinct stellar populations

13 Globular Clusters: A New Frontier for the AGB and a new Opportunity to Understand it Multiple stellar generations are ubiquitous among Globular Clusters Secondary, tertiary populations are helium rich and made of material heavily processed by p-captures at high temperatures (~108 K)

14 Globular Clusters: A New Frontier for the AGB and a new Opportunity to Understand it Multiple stellar generations are ubiquitous among Globular Clusters Secondary, tertiary populations are helium rich and made of material heavily processed by p-captures at high temperatures (~108 K) In the least unplausible scenario this material is provided by 3-10 M AGB & Super-AGB stars. Opportunity: understanding multiple populations in GCs and understanding AGB evolution is one problem and the same!

15 What we would like to know on AGB Stars Yields of He, Li, C, N, O, Ne, Na, Mg, Al, s-process Mass of H and He burned during the AGB phase contribution to the light (SED) of stellar populations Time spent and max luminosity reached on AGB All this as a function of initial stellar mass (and comp.) Stellar models can predict these quantities as functions of various, arbitrary input parameters, but they are almost certainly wrong. Better try to measure these things, using Multiple pop.s in globular clusters in the MW and in the MCs and in low-and high-redshift galaxies

16 Thank You!

Gas and dust pollution. from AGB stars.

Gas and dust pollution. from AGB stars. Osservatorio Astronomico di Roma Gas and dust pollution from AGB stars. Marcella Di Criscienzo INAF-Osservatorio Astronomico di Roma Collaborators: P. Ventura, F. Dell Agli, F. D Antona, A. Karakas, A.