Transcript MASSIVE STARS

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 system
e.g. when metallicity reached a given value, or when some
stellar source (SNIa, AGB etc.) became important contributor
to 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
AGE-METALLICITY
METALLICITY
DISTRIBUTION
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)
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
Salaris and Weiss 2002
AGES OF
HALO STARS
Marquez and Schuster 1994
Norris and Ryan 1991
OUTFLOW
INFALL
AGE – METALLICITY IN THE GALACTIC HALO
Stars of mass M > 2 Mʘ (Lifetime < 1 Gyr)
enriched the Galaxy during the halo phase
Note: Instantaneous mixing approximation probably invalid at early times
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!)
STELLAR CNO YIELDS
NITROGEN
PRODUCTION
Non Rotating:
MASSIVE STARS (107 years):
Secondary
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
EVOLUTION OF CNO IN SOLAR NEIGHBORHOOD
C and N abundances
always follow Fe
PRIMARIES ?
But: 2/3 of Fe in disk
come 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 N
in early halo:
Which primary source?
Secondary N production
at late times matches
Fe production from SNIa
[N/Fe]  0
Not exactly the case for C…
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!
FRACTIONAL CONTRIBUTION
TO NITROGEN-14 PRODUCTION
FRACTIONAL CONTRIBUTION
TO CARBON-12 PRODUCTION
PRIMARY NITROGEN…
WITH RESPECT TO WHAT ???
WW95 + VdHG97
MM02 No Rot
MM02 + Rot
PSEUDO-SECONDARY BEHAVIOUR
WITH RESPECT TO OXYGEN
THE MILKY WAY DISK
Inside-Out formation and radially varying SFR efficiency required to reproduce
observed SFR, gas and colour profiles (Scalelengths: RB4 kpc, RK2.6 kpc)
(Boissier and Prantzos 1999)
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 gradients
were 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
ABUNDANCE GRADIENTS OF CNO IN MILKY WAY DISK
C and O not sensitive
to different sets of yields
(primaries)
For N, stellar yields
up to Z=3 Z⊙
(not available at present)
are required in order
to model the inner disk