Paola Marigo Department of Physics and Astronomy G. Galilei University of Padova, Italy MASS LOSS IN EVOLUTIONARY MODELS OF LOW  AND INTERMEDIATE  MASS STARS

OUTLINE  Mass loss on the Red Giant Branch  old and new formalisms  old and new methods to probe RGB mass loss  predicted metallicity dependence  dust formation   Mass loss on the Asymptotic Giant Branch  many different available formalisms  impact on evolutionary properties (lifetimes, nucleosynthesis, final masses)  a global calibration method based on EPS models of galaxies

MASS LOSS ACROSS THE H-R DIAGRAM Mass loss measurements across the H-R diagram (Cranmer & Saar 2011, ApJ, 741, 54)

Significant mass loss takes place during 2 evolutionary phases, both along the Hayashi lines: I.In red giants, before the onset of large-amplitude pulsation. Typical mass-loss rates are low,  M ʘ / yr. Where: on the Red Giant Branch and Early AGB Main form of mass loss in the lowest mass evolved stars, i.e. globular cluster stars. II.In TP-AGB stars after the onset of large amplitude pulsation (Mira). Typical mass-loss rates are large, up to M ʘ / yr (super-winds). MASS LOSS FROM LOW- AND INTERMEDIATE- MASS STARS (0.8  M/M   6-8)

MASS LOSS ON THE RGB WHICH IS THE DRIVING MECHANISM? Dissipation of mechanical energy generated in the convection zone? Acoustic or magnetic waves? (Fusi Pecci & Renzini 1975) No definitive theoretical model yet. Usual recipe: Reimers’ Law for mass loss (Reimers (1975) Basic assumption: the rate of gravitational energy carried out in the wind is proportional to the stellar luminosity (dimensional scale argument) No physical interpretation of the wind mechanism adjustable parameter  0.35  0.45

A MODIFIED REIMERS' LAW BASED ON A PHYSICAL APPROACH (SCHRÖDER & CUNTZ 2005, 2007) Wind energy balance From modelling of mechanical energy flux: convective turbulence => magnetic+acoustic waves Mechanical luminosity Chromospheric radius  = =

A RECENT THEORETICAL APPROACH (CRANMER  SAAR 2011) Wind models for cool MS and evolved giants based on magnetohydrodynamic turbolence in the convective subsurface zones. G  K dwarfs: winds driven by gas pressure from hot coronae Red giants: winds driven by Alfvén wave pressure F A* = Alfvén wave energy f * = filling factor Schröder & Cuntz (2005) assume dM/dt  F A* Hot coronae Cold Alfvén waves

WHAT ARE THE HINTS FOR MASS LOSS ON THE RGB? CCG M 

MULTIPLE POPULATIONS IN CCGS AND HELIUM CONTENT Lee et al. (2005, ApJ, 621, L57) Several authors have recently suggested that multiple populations with widely varying levels of He abundance may be present in GCs. The extended blue HB may be explained with high He content. This fact would weaken the RGB mass-loss calibration method based on the HB morphology. NGC 2808 (Z=0.0014, age=10.1 Gyr)

PULSATION MODELS FOR 47 TUC VARIABLES: INFERENCE OF MASS LOSS From theoretical PMR relations Lebzelter  Wood (2005) concluded that observations of  Tuc variables are recovered invoking mass loss operating on the RGB (Reimers Law) and AGB. A total amount of .  M  ejected mass is required.

DO CURRENT RGB PRESCRIPTIONS OVERESTIMATE MASS LOSS  Meszaros et al Mass loss rates of RGB and AGB stars in GGCs (M , M , M  ) from chromospheric models of the H  line Mass loss increases with L and with decreasing T EFF Suggestion of metallicity dependence Rates are ~order magnitude less than ‘Reimers’ and IR results

Independent constraints on masses and radii of RGB stars from Kepler data Solar  like oscillation spectra: frequency spacing frequency of maximum power ASTEROSEISMOLOGY: INTEGRATED RGB MASS LOSS NGC 6791: a metal  rich old open cluster with  Fe  H  and age  Gyr  Red Giant Branch stars  Red Clump stars             Miglio et al. 2012, MNRAS, 419, 2077

PREDICTED METALLICITY DEPENDENCE ON THE RGB Kalirai J S, Richer H B Phil. Trans. R. Soc. A 2010;368: age  Gyr all nomalized to   at  Fe  H  Big spread at increasing Z! Asteroseismologic estimate at age  Gyr

DUST OR NOT DUST ON THE RGB  A WORD FROM THEORY In between the observational debate of Origlia et al vs Boyer et al (see also Momany et al. 2012, Groenewegen 2012) a strong theoretical conclusion by Gail et al. 2009, ApJ, 698, 1033 Fraction of the element Si condensed into forsterite grains on the tip of the RGB, with maximum possible growth coefficient. Condensation factor very low for all initial masses and metallicities, except perhaps for stars of    and    Unfavorable conditions of RGB winds: transition to a highly supersonic outflow occurs close to the star where temperatures are too high for dust formation.

THE TP-AGB PHASE Dusty circumstellar envelope atmosphere convective envelope energy sources and nucleosynthesis

PULSATION: A KEY INGREDIENT A very rapid rise in Mdot with P to “superwind” values. Then a very slow increase. No information on any mass dependence; large variation at a given P. Based on CO microwave observations in the wind outflow ( Vassiliadis & Wood 1993) Derived by fitting dust envelope models to the combined Spitzer 5-35 micron spectra and simultaneous JHLK photometry (Groenewegen et al. 2007).

THE ONSET OF THE SUPER WIND: A CRITICAL ISSUE The luminosity of termination of AGB evolution (complete envelope ejection) is determined by the period (luminosity) at which Mdot rises rapidly to "superwind" values. Observations: The dust-enshrouded AGB stars are all large amplitude pulsators. Theory: The transition to a superwind is dictated by large amplitude pulsation + dust + radiation pressure (large L)

MASS-LOSS RECIPES  Vassiliadis & Wood (1993) [empirical, CO microwave estimates of Mdot, plotted against pulsation period]  Bowen (1988) and Bowen & Willson (1991) [computed mass loss rates with simplistic energy loss mechanisms and grain opacities]  Blöcker (1995) [formula based on Bowen (1988)]  Groenewegen (1998) [C star mass loss rates in solar vicinity]  Wachter et al (2002; 2008) [C star pulsation/mass loss models]  Groenewegen et al (2007) [C star mass loss rates in the LMC and SMC from Spitzer observations]  Van Loon et al. (2005) [O-rich dust-enshrouded AGB and RSG stars in the LMC]  Mattsson et al. (2010) [C star pulsation/mass loss models] O-rich models lacking [see Jeong et al. (2003), and S. Hoefner this workshop] empirical theoretical

AGB MASS LOSS: IMPACT ON EVOLUTIONARY MODELS TP-AGB evolutionary features are dramatically affected by the adopted mass-loss recipe: Lifetimes Determines the number of thermal pulses Luminosities AGB tip, HBB over-luminosity of massive AGB stars Final masses Limits the growth of the core mass Nucleosynthesis Limits the number and the efficiency of dredge-up episodes; affects the HBB nucleosynthesis

COMPARING DIFFERENT MASS-LOSS FORMALISMS: M I =2.0M ʘ Z I =0.008 Vassiliadis & Wood 1993 SW at P=800 days Bloecker 1995 Wachter et al Marigo et al. 2012

AGB MASS LOSS AND WIND PROPERTIES Vassiliadis & Wood 1993Vassiliadis & Wood 1993 with SW at P=800 days Models: Nanni et al. 2012, in prep.  M i =2M   M i =3M   M i =4M 

CHEMICAL YIELDS Stancliffe  Jeffery 2007, MNRAS, 375, 1280 M i .     Yields relative difference:  C   other light elements   Fe group elements up to a factor of 2

MASS LOSS AND HOT BOTTOM BURNING IN MASSIVE AGB STARS Mi    Ventura  DAntona 2005

MASS LOSS AND HOT BOTTOM BURNING IN A (M I =5 M  Z=0.008) MODEL Vassiliadis & Wood 1993 Bowen & Willson Wachter et al Marigo et al. in prep.

NUCLEOSYNTHESIS AND MOLECULAR CHEMISTRY Vassiliadis & Wood 1993 Bowen & Willson Wachter et al Marigo et al. in prep.

AGB MASS LOSS: CALIBRATING OBSERVABLES AGB mass loss can be constrained combining accurate evolutionary models with population synthesis simulations Lifetimes number counts of AGB stars in star clusters and galaxy fields Luminosities luminosity, color, and period distributions Central star’s mass (WD) initial-final mass relation and WD mass distribution Nucleosynthesis M-C transition L in clusters, (3° dredge-up and HBB) C/O values, Li-rich AGB stars PN abundances test

STANDARD CALIBRATORS: AGB STARS IN MAGELLANIC CLOUDS’ CLUSTERS  Vassiliadis & Wood 1993 Marigo et al. 2012

STANDARD CALIBRATORS: AGB STARS IN MAGELLANIC CLOUDS’ CLUSTERS  Vassiliadis & Wood 1993  Bloecker 1995 Marigo et al. 2012

STANDARD CALIBRATORS: AGB STARS IN MAGELLANIC CLOUDS’ CLUSTERS  Vassiliadis & Wood 1993  Bloecker 1995  Bowen & Willson 1991 (C/O<1)  Wachter et al (C/O>1) Marigo et al. 2012

STANDARD CALIBRATORS: AGB STARS IN MAGELLANIC CLOUDS’ CLUSTERS  Vassiliadis & Wood 1993  Bloecker 1995  Bowen & Willson 1991 (C/O<1)  Wachter et al (C/O>1)  Van Loon et al (C/O<1)  Wachter et al (C/O>1) Marigo et al. 2012

STANDARD CALIBRATORS: AGB STARS IN MAGELLANIC CLOUDS’ CLUSTERS  Vassiliadis & Wood 1993  Bloecker 1995  Bowen & Willson 1991 (C/O<1)  Wachter et al (C/O>1)  Van Loon et al (C/O<1)  Wachter et al (C/O>1)  Kamath et al 2011 (C/O>1) VW93 + SW delayed at P=800 days Marigo et al. 2012

STANDARD CALIBRATORS: AGB STARS IN MAGELLANIC CLOUDS’ CLUSTERS  Vassiliadis & Wood 1993  Bloecker 1995  Bowen & Willson 1991 (C/O<1)  Wachter et al (C/O>1)  Van Loon et al (C/O<1)  Wachter et al (C/O>1)  Kamath et al 2011 (C/O>1) VW93 + SW delayed at P=800 days  Vassiliadis & Wood 1993 (C/O<1)  Arndt et al (C/O>1) Marigo et al. 2012

A NEW CALIBRATION APPROACH: ANGST THE ACS NEARBY GALAXY SURVEY TREASURY (DALCANTON ET AL. 2009; GIRARDI ET AL. 2010) High accuracy optical multiband photometry of 62 galaxies outside the Local Groups (within 4 Mpc). 12 selected galaxies: metal poor [Fe/H]  -1.2 and dominated by old stars, with ages > 3 Gyr (0.8 M ⊙  Mi  1.4 M ⊙ ). Derivation of SFH from CMD fitting based on Marigo et al. (2008) isochrones.

AGB STARS IN THE ANGST GALAXIES RGB and AGB stars detected Counts of AGB stars brigther than the RGB tip Typically N AGB  per galaxy N AGB /N RGB  – Simulations of galaxies: TRILEGAL (Girardi et al.2005) multi band mock catalogues of resolved stellar populations, for given distance, SFR, AMR

OBSERVATIONS VS MODELS Predicted AGB stars too many too bright

CURING THE DISCREPANCY: MORE EFFICIENT MASS LOSS ON THE AGB AT LOW Z AND OLD AGES Schroeder & Cuntz Bedjin (1998) like dust- driven mass loss Shorter TP-AGB lifetimes Fainter luminosiites Lower final masses (WDs) White Dwarf mass measurements in M4 (Kalirai et al. 2009, ApJ, 705, 408)

before after

SNAP (Dalcanton et al. 2011, ApJS, 198, 6) snapshot survey of 62 galaxies (26 observed) with the near IR filters WFC3/IR F110W+F160W SFH from optical CMDs Complete census of AGB stars from near IR

SFH from optical CMDs Complete census of AGB stars from near IR SNAP-11719:snapshot survey of 62 galaxies (26 observed) with the near IR filters WFC3/IR F110W+F160W (Dalcanton et al. 2011, ApJS, 198, 6) MS bCHeB rCHeB AGB RGB

RGB + AGB stars responsible for 21% + 17% of the integrated flux emitted by galaxies in the near IR Present TP-AGB models show an average excess:  50% in the predicted lifetimes,  factor of 2 in the emitted flux ODD! Models are calibrated on direct counts of AGB stars in MC clusters. Possible relevant impact in EPS models of galaxies and mass determination of high-z objects (Bruzual 2009). Melbourne et al. 2012, ApJ, 748, 47

THE INITIAL  FINAL MASS RELATION: DEPENDENCE ON MASS-LOSS EFFICIENCY

THE INITIAL  FINAL MASS RELATION: THE 3° DREDGE-UP PLAYS A ROLE!  Mc = M f- M c,1tp a lower limit to the effective nuclear fuel burnt (hence lifetime) during the TP-AGB. Present models of intermediate mass AGB stars predict a very efficient 3° dredge-up (  ), with practically no growth of Mc (Karakas et al. 2010, Stancliffe et al. 2009).

THE INITIAL  FINAL MASS RELATION: DEPENDENCE ON METALLICITY Marigo  Girardi 2007 Karakas 2010 Non monotonic trend with ZMonotonic trend with Z

CONCLUDING REMARKS  RGB mass loss  The classical methodology (Reimers law + HB morphology in GGCs) is currently debated due to  Alternative, more physically sound, mass-loss prescriptions  new scenario of GGCs: multiple stellar populations and He content  new observational/theoretical techniques (asteroseismology, pulsation models, infrared data)  From theory: tiny, if not any, amount of dust on the RGB at subsolar Z  AGB mass loss  Onset of the superwind, a critical point still uncertain (M, Z, C/O, L, Teff, P)  Evolutionary properties heavily affected by the adopted mass-loss law  Initial-final mass relation: mass loss and third dredge-up both concur to shape it.  Calibration needed! Population synthesis of AGB stars in clusters and in fields of galaxies, covering a large range of ages and metallicities. Ongoing work.