Paola MarigoDepartment of Physics and Astronomy G. GalileiUniversity of Padova, Italy

MASS LOSS IN EVOLUTIONARY MODELS OF

LOW AND INTERMEDIATEMASS 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, 10-8 Mʘ/yr . Where: on the Red Giant Branch and Early AGBMain 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 10-4 Mʘ/yr (super-winds) .

MASS LOSS FROM LOW- AND INTERMEDIATE- MASS

STARS (0.8 M/M 6-8)

MASS LOSS ON THE RGBWHICH 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 mechanism𝑑𝑀𝑑𝑡

𝐺𝑀𝑅 ∝𝐿⇒ 𝑑𝑀

𝑑𝑡 =𝜂 𝐿𝑅𝑀

adjustable parameter 0.350.45

A MODIFIED REIMERS' LAWBASED 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 onmagnetohydrodynamic turbolence in the convectivesubsurface zones.GK dwarfs: winds driven by gas pressure from hot coronaeRed giants: winds driven by Alfvén wave pressure

FA*= Alfvén wave energyf*= filling factor

Schröder & Cuntz (2005) assume dM/dt FA*

Hot coronae

Cold Alfvén waves

WHAT ARE THE HINTS FOR MASS LOSS ON THE RGB?

Classical inference (Renzini & Fusi Pecci 1988) Typical globular cluster turnoff

mass is 0.85 M.Masses of RR Lyrae stars (on the Horizontal Branch, following He coreignition at the tip of the First Giant Branch) are 0.65 M (from pulsationtheory).Hence, ~0.20 M is lost between the main-sequence and the Horizontal Branch.

~0.20 M is the mass that should be lost to account for the morphology

of the extended blue Horizontal Branches in the HR diagrams of GGCs.

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 relationsLebzelter Wood (2005) concludedthat observations of Tuc variables arerecovered invoking mass loss operatingon the RGB (Reimers Law) and AGB.

A total amount of . M ejected massis required.

DO CURRENT RGB PRESCRIPTIONS OVERESTIMATE MASS LOSS

Meszaros et al. 2009

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 TEFF

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 dataSolarlike oscillation spectra:

frequency spacing frequency of maximum power

ASTEROSEISMOLOGY: INTEGRATED RGB MASS LOSS

NGC 6791: a metalrich old open cluster with FeH and age Gyr

Red Giant Branch stars Red Clump stars

Miglio et al. 2012, MNRAS, 419, 2077

PREDICTED METALLICITY DEPENDENCEON THE RGB

Kalirai J S , Richer H B Phil. Trans. R. Soc. A 2010;368:755-782

age Gyrall nomalized to at FeH

Big spread at increasing Z!

Asteroseismologic estimateat age Gyr

DUST OR NOT DUST ON THE RGBA WORD FROM THEORY

In between the observational debate of Origlia et al. 2010 vs Boyer et al. 2010(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 outflowoccurs close to the star where temperatures are too high for dust formation.

THE TP-AGB PHASE

Dusty circumstellar envelope

atmosphere

convective envelope

energy sources andnucleosynthesis

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 observationsin the wind outflow (Vassiliadis & Wood 1993)

Derived by fitting dust envelope models to thecombined 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 estimatesof Mdot, plotted against pulsation period] Bowen (1988) and Bowen & Willson (1991) [computed mass loss rates with simplistic energy loss mechanisms and grainopacities] 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 LMCand 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=2.0Mʘ Z I=0.008

Vassiliadis & Wood 1993

Vassiliadis & Wood 1993SW at P=800 days

Bloecker 1995

Wachter et al. 2008

Marigo et al. 2012

AGB MASS LOSS AND WIND PROPERTIES

Vassiliadis & Wood 1993 Vassiliadis & Wood 1993 with SW at P=800 days

Models: Nanni et al. 2012, in prep. Mi=2M Mi=3M Mi=4M

CHEMICAL YIELDS

Stancliffe Jeffery 2007, MNRAS, 375, 1280

Mi.

Yields relative difference:C other light elements Fe group elements up to a factor of 2

MASS LOSS AND HOT BOTTOM BURNING

IN A (M I=5 M Z=0.008) MODELVassiliadis & Wood 1993 Bowen & Willson 1991 + Wachter et al. 2008

Marigo et al. in prep.

NUCLEOSYNTHESIS AND MOLECULAR CHEMISTRY

Vassiliadis & Wood 1993 Bowen & Willson 1991 + Wachter et al. 2008

Marigo et al. in prep.

AGB MASS LOSS: CALIBRATING OBSERVABLES

AGB mass loss can be constrained combining accurate evolutionarymodels 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

test

test

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. 2008 (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. 2008 (C/O>1)

Van Loon et al. 2005 (C/O<1) Wachter et al. 2008 (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. 2008 (C/O>1)

Van Loon et al. 2005 (C/O<1) Wachter et al. 2008 (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. 2008 (C/O>1)

Van Loon et al. 2005 (C/O<1) Wachter et al. 2008 (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. 1997 (C/O>1)

Marigo et al. 2012

A NEW CALIBRATION APPROACH: ANGSTTHE 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] -1.2and 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 detectedCounts of AGB stars brigther than the RGB tipTypically NAGB 60 - 400 per galaxyNAGB/NRGB 0.023 – 0.050

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 starstoo many too bright

CURING THE DISCREPANCY:MORE EFFICIENT MASS LOSS ON THE

AGBAT LOW Z AND OLD AGES

Schroeder & Cuntz 2005+ Bedjin (1998) like dust-driven mass loss

Shorter TP-AGB lifetimes

Fainter luminosiites

Lower final masses (WDs)

White Dwarf mass measurements inM4 (Kalirai et al. 2009, ApJ, 705, 408)

before after

SNAP-11719(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 AGBstars from near IR

SFH from optical CMDs

Complete census of AGBstars 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)

MSbCHeB

rCHeB

AGB

RGB

RGB + AGB stars responsible for 21% + 17% of the integrated fluxemitted by galaxies in the near IR

Present TP-AGB models showan 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 EPSmodels of galaxies and massdetermination of high-z objects(Bruzual 2009).

Melbourne et al. 2012, ApJ, 748, 47

THE INITIALFINAL MASS RELATION:DEPENDENCE ON MASS-LOSS

EFFICIENCY

THE INITIALFINAL MASS RELATION:THE 3° DREDGE-UP PLAYS A ROLE!

Mc = Mf-Mc,1tp a lower limit to the effectivenuclear 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 INITIALFINAL MASS RELATION:DEPENDENCE ON METALLICITY

Marigo Girardi 2007 Karakas 2010

Non monotonic trend with Z Monotonic 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.