aims of g alactic c hemical e volution studies
DESCRIPTION
AIMS OF G ALACTIC C HEMICAL E VOLUTION 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 system - PowerPoint PPT PresentationTRANSCRIPT
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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
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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
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Woosley and Weaver 1995, Overproduction factors of elements in massive stars
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ABUNDANCES AT SOLAR SYSTEM FORMATION(Massive stars: Woosley+Weaver 1995; Intermediate mass stars: van den Hoek+Gronewegen 1997;
SNIa: Iwamoto et al. 2000)
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AGES OF GLOBULAR CLUSTERS
AGES OFHALO STARS
Marquez and Schuster 1994
Salaris and Weiss 2002
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Norris and Ryan 1991
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INFALL
OUTFLOW
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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
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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!)
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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
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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
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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…
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FRACTIONAL CONTRIBUTIONTO NITROGEN-14 PRODUCTION
FRACTIONAL CONTRIBUTIONTO CARBON-12 PRODUCTION
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PRIMARY NITROGEN…WITH RESPECT TO WHAT ???
WW95 + VdHG97MM02 No RotMM02 + Rot
PSEUDO-SECONDARY BEHAVIOURWITH RESPECT TO OXYGEN
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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
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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
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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
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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
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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
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