metallicity dependence of winds from red supergiants and asymptotic giant branch stars

Metallicity Dependence of Winds from

Red SuperGiants and

Asymptotic Giant Branch Stars

Jacco van LoonKeele

University

Jacco van LoonKeele

University

Dust wind structure

Radiative equilibrium + continuity equation:

Spectral Energy Distribution

Spectral Energy Distribution

• Integral luminosity

Spectral Energy Distribution

• Integral luminosity• Shape optical depth

Spectral Energy Distribution

• Integral luminosity• Shape optical depth

… but measuring mass-loss rate requires:

• Dust-to-gas ratio

Spectral Energy Distribution

• Integral luminosity• Shape optical depth

… but measuring mass-loss rate requires:

• Dust-to-gas ratio• Wind speed

Dust wind structure

Momentum equation:

Gail & Sedlmayr (1986)

Dust wind structure

Large Magellanic Cloud

Parkes radio observatory

Wind speed from OH masers

Wood et al. (1992)

Marshall et al. (2004)

Wind speed

Wind speed

For oxygen-rich stars

LMC versus the Milky Way

Van Loon (2000)

Mass-loss rate

Mass-loss rate

For oxygen-rich stars

van Loon et al. (1999) + new MSX sample

Superwind mass-loss ratesConversion of radiative momentum:

Superwind mass-loss ratesConversion of radiative momentum:

Multiple scattering:

Gail & Sedlmayr (1986)

Superwind mass-loss rates

Multiple scattering limit predicts:

Superwind mass-loss rates

Multiple scattering limit predicts:

LMC versus galactic bulge

Alard et al. (2001)

Temperature and evolution

Alard et al. (2001)

Galactic bulge observations:

Temperature and evolution

Alard et al. (2001)

Galactic bulge observations:

Hydrodynamic models (carbon stars):

Arndt, Fleischer & Sedlmayr (1997)

Wachter et al. (2002)

Superwind stars in the LMC

luminosity, metallicity (20-25% solar), mass

Cluster superwind carbon star LI-LMC 1813:

Van Loon et al. (2003)

Superwind stars in the LMC

luminosity, metallicity (20-25% solar), mass

Cluster superwind carbon star LI-LMC 1813:

Van Loon et al. (2003)

Wachter et al. (2002)

Compare with solar metallicity model:

Superwind stars in the LMC

Van Loon et al. (2005)

Superwind stars in the LMC

For oxygen-rich stars

LMC prediction applied to Milky Way

Van Loon et al. (2005)

Small Magellanic Cloud

Small Magellanic Cloud

47 Tucanae

SMC versus the LMC

Mass-loss rate

For oxygen-rich and carbon stars

LMC + corrected SMC from Groenewegen et al. (2000)

Z-independent mass-loss rate?

Z-independent mass-loss rate?

(above ~0.1 solar metallicity)

Z-independent mass-loss rate?

(above ~0.1 solar metallicity)

WHY ?

Pulsation in LMC superwind stars

Whitelock et al. (2003)

Pulsational energy

Absolute maximum = 0.5

Pulsation during the superwind

Similar limit for Milky Way, LMC, SMC

Pulsation during the superwind

Similar limit for Milky Way, LMC, SMC

Pulsation during the superwind

Similar limit for Milky Way, LMC, SMC

Hence similar (maximum) mass-loss rates?

Molecule formation

Van Loon et al. (1998)

Molecule formation

• LMC: AGB up to M10; RSG up to M7

Molecule formation

• LMC: AGB up to M10; RSG up to M7

• SMC: AGB up to M8; RSG up to M5Groenewegen & Blommaert (1998)

ESO-VLT

Magellanic carbon stars

Magellanic carbon stars

Van Loon, Zijlstra & Groenewegen (1999)Matsuura et al. (2002, 2005)

Magellanic carbon stars

Large(r?) molecular abundances at low Z

Magellanic carbon stars

Large(r?) molecular abundances at low Z

Especially C2 and C2H2 (not CN and HCN)

Magellanic carbon stars

Large(r?) molecular abundances at low Z

Especially C2 and C2H2 (not CN and HCN)

Due to lower O (and N) abundances

Metal-poor carbon star winds

What if in metal-poor carbon stars...

Metal-poor carbon star winds

What if in metal-poor carbon stars...

… the dust-to-gas ratio were higher...

Metal-poor carbon star winds

What if in metal-poor carbon stars...

… the dust-to-gas ratio were higher...

… their winds would be faster...

Metal-poor carbon star winds

What if in metal-poor carbon stars...

… the dust-to-gas ratio were higher...

… their winds would be faster...

… but their mass-loss rates the same (?)

Spitzer Space Telescope

Molecules in magellanic winds

Spitzer GO programme 3505 (Peter Wood)

CO in magellanic winds

• measure dust-to-CO ratio

• measure carbon star wind speed

Conclusions (to be continued)

above ~0.1 solar metallicity:

Conclusions (to be continued)

• mass-loss rates independent of Z

above ~0.1 solar metallicity:

Conclusions (to be continued)

• mass-loss rates independent of Z• metal-poor O-rich stars are less dusty

above ~0.1 solar metallicity:

Conclusions (to be continued)

• mass-loss rates independent of Z• metal-poor O-rich stars are less dusty• slower winds of metal-poor O-rich

stars

above ~0.1 solar metallicity:

Conclusions (to be continued)

• mass-loss rates independent of Z• metal-poor O-rich stars are less dusty• slower winds of metal-poor O-rich

stars• … smaller momentum injection rate

above ~0.1 solar metallicity:

Conclusions (to be continued)

• mass-loss rates independent of Z• metal-poor O-rich stars are less dusty• slower winds of metal-poor O-rich stars• … smaller momentum injection rate• are metal-poor carbon stars less dusty?

above ~0.1 solar metallicity:

Conclusions (to be continued)

• mass-loss rates independent of Z• metal-poor O-rich stars are less dusty• slower winds of metal-poor O-rich stars• … smaller momentum injection rate• are metal-poor carbon stars less dusty?• wind speed of metal-poor carbon stars: ?

above ~0.1 solar metallicity:

Conclusions (to be continued)

• mass-loss rates independent of Z• metal-poor O-rich stars are less dusty• slower winds of metal-poor O-rich stars• … smaller momentum injection rate• are metal-poor carbon stars less dusty?• wind speed of metal-poor carbon stars: ?

above ~0.1 solar metallicity:

Below ~0.1 solar metallicity: ?