AIMS OF GALACTIC CHEMICAL EVOLUTION STUDIES

To check / constrain our understanding of stellar nucleosynthesis(i.e. stellar yields), either statistically (mean, dispersion) or in

individual objects

To establish a chronology of events in a given systeme.g. when metallicity reached a given value, or when some

stellar source (SNIa, AGB etc.) became important contributorto the abundance of a given isotope / element

To infer how a system was formed (Star Formation Rate, large scale gas mouvements)

e.g. slow infall of gas in case of solar neighborhood

THE SOLAR NEIGHBORHOOD

SLOW INFALL ( = 7 Gyr) to fix G-dwarf problem, SNIa to account for [Fe/O] evolution

PREDICTIONS: D evolution, evolution of abundances (depends on yields)

AGE-METALLICITY METALLICITYDISTRIBUTION

Woosley and Weaver 1995, Overproduction factors of elements in massive stars

ABUNDANCES AT SOLAR SYSTEM FORMATION(Massive stars: Woosley+Weaver 1995; Intermediate mass stars: van den Hoek+Gronewegen 1997;

SNIa: Iwamoto et al. 2000)

AGES OF GLOBULAR CLUSTERS

AGES OFHALO STARS

Marquez and Schuster 1994

Salaris and Weiss 2002

Norris and Ryan 1991

INFALL

OUTFLOW

AGE – METALLICITY IN THE GALACTIC HALO

Note: Instantaneous mixing approximation probably invalid at early times

Stars of mass M > 2 Mʘ (Lifetime < 1 Gyr)enriched the Galaxy during the halo phase

NOTE: PRIMARIES VS SECONDARIES

1) CHEMICAL EVOLUTION (yield: IMF integrated or individual stars)

PRIMARY: yield yP independent of Z

SECONDARY: yield yS proportional to Z

2) STELLAR NUCLEOSYNTHESIS (yield from individual stars)

PRIMARY: from H, He and their products (C,O)(yield not necessarily Z independent!)

SECONDARY: from some metal at stellar formation(yield not necessarily proportional to Z!)

NITROGENPRODUCTION

MASSIVE STARS (107 years): SecondaryNon Rotating: INTERMEDIATE MASS (108 years): Primary

LOW MASS STARS (109 years): Secondary

Rotating: MASSIVE STARS (107 years): Secondary Stars INTERMEDIATE AND LOW MASS (108 years): Primary

STELLAR CNO YIELDS

C and N abundancesalways follow Fe

PRIMARIES ?

But: 2/3 of Fe in diskcome late from SNIa

⇩2/3 of C and N in disk

come from a late source

(not operating in halo) Low mass stars ?

Secondary N (but C?) Z-dependent yields

from massive stars?

No sign of secondary Nin early halo:

Which primary source?

EVOLUTION OF CNO IN SOLAR NEIGHBORHOOD

Stellar rotation has similar effect on

yields of nitrogen(mostly from

Intermediate mass stars)as Hot Bottom Burning

Difficult to explain earliest primary Nitrogen(Massive star yields insufficient

-even with rotation…)However: timescales at low [Fe/H] uncertain!

Secondary N production at late times matchesFe production from SNIa

[N/Fe] 0Not exactly the case for C…

FRACTIONAL CONTRIBUTIONTO NITROGEN-14 PRODUCTION

FRACTIONAL CONTRIBUTIONTO CARBON-12 PRODUCTION

PRIMARY NITROGEN…WITH RESPECT TO WHAT ???

WW95 + VdHG97MM02 No RotMM02 + Rot

PSEUDO-SECONDARY BEHAVIOURWITH RESPECT TO OXYGEN

Inside-Out formation and radially varying SFR efficiency required to reproduce

observed SFR, gas and colour profiles (Scalelengths: RB4 kpc, RK2.6 kpc)(Boissier and Prantzos 1999)

THE MILKY WAY DISK

METALLICITY PROFILE OF MILKY WAY DISK

Present day gradient : dlog(O/H)/dR ∼ - 0.07 dex/kpc

Models predict (e.g. Hou et al. 2000) that abundance gradientswere steeper in the past

METALLICITY PROFILE OF MILKY WAY DISK

Recent observations (Maciel et al 2002) of planetary nebulae

of various ages support that prediction:

The disk was formed inside-out

“Observed” evolution of O gradient:

d[dlog(O/H)/dR]/dt ∼ 0.004 dex/kpc/Gyr

In broad agreement with theory

ABUNDANCE GRADIENTS OF CNO IN MILKY WAY DISK

O: dlog(O/H) / dR = - 0.07 dex/kpc

But: Deharveng et al. (2001): -0.04 dex/kpc

N: dlog(N/H) / dR = - 0.08 dex/kpc

C: dlog(C/H) / dR = - 0.07 dex/kpc

C and O not sensitiveto different sets of yields

(primaries)

For N, stellar yieldsup to Z=3 Z⊙

(not available at present)are required in order

to model the inner disk

ABUNDANCE GRADIENTS OF CNO IN MILKY WAY DISK