Chemical evolution in the MW Observational evidence. Birgitta Nordström Niels Bohr Institute. Outline. First (oldest) stars in MW halo Long-lived stars in MW disk Age determination. Motivation for study.
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Niels Bohr Institute
”The formation and evolution of galaxies is one of the great outstanding problems in astrophysics.”
(Freeman & Bland-Hawthorn, 2002)
We think we know the grand scheme of the story,
but how well do we understand the real physics ?
Progress reported in Copenhagen, June 2008 (Proceedings in 09).
How do we know if/that the MW evolves?
(hydrogen, helium, deuterium, lithium)
Halo+bulge formation (thick disk?)
Thin Disk formation
Elements “pollute” ISM
Interstellar Medium (ISM)
IMF + SFR
Stellar mass loss
Stellar death - (m)
SN type II(core collapse)
(M > 8 M)
Fe and r-process elements up to U
Low- and Interm.-mass Stars
(0.8 < M < 8 M )
Planetary Nebulae, ..
He, C, N, heavy
Binary st. (WD)
SN type Ia(thermonuclear explosion)
Sun = 1
”Standard Big Bang”:
there was formed
and 150 7Li
Average density /0
(Baryon to photon ratio)
WMAP + SBBNS
New Li produced by cosmic radiation
and in stars
at the same time …
Li is destroyed
Videre opad i det
Generel tendens: færre tunge kerner
r-proces toppe (lukkede kerneskaller)
s-proces toppe (lukkede kerneskaller)
”Katteøjet” planetariske tåger ”Håndvægten”
”Crab nebula”: Supernova 1054 – 950 years after
Optical (ESO VLT) X-rays (Chandra)
Models by Nomoto et al.
Elemental abundances predicted for various progenitor mass and explosion energies.
Cayrel et al. (2001)
from star of [Fe/H] ~ -3
? Is that the age of the MW or what is the origin of the star (and similar)?
4He + 4He 8Be
8Be + 4He 12C + g
12C burning (<1000 years)
12C + 4He 16O
12C + 12C 20Ne + 4He + g
16O burning (<1 year)
16O + 16O 28Si + 4He + g
12C + 16O 24Mg + 4He + g
25M 20M 13M
incomplete explosive Si burning
‘swallow’ more of the core (Fe, Co, Ni), when the star collapses to a black hole or a neutron star.
complete explosive Si burning
- slowly in those elements produced by SNIa and low- and intermediate mass stars (Fe, C, N)
Detailed analysis of
189 nearby longlived
stars relative to the Sun
(Edvardsson et al.,1993)
([X/H] = log(X/H) –log(X/H)sun)
SN II enrichment
SN Ia + SNII +PN +..
Halo + thick disk
Spherical dense clusters
of about 106 stars
Searle and Zinn (1978):
GC have different metallicities independent of distance from Galactic Centre.
Important for Galaxy formation
Messier 10 - a globular
cluster in the Galaxy
The Milky Way has about 150 of these clusters
High-mass stars evolved onto the giant branch
Low-mass stars still on the main sequence
relative to the sun.
abundances, down to [Fe/H] < -5
Study the disk as that is where most of the baryons are.
Complete, magnitude limited sample of FG dwarfs
Teff from uvby photometry
Integrate probability for all points in diagram
= ’Well-defined’ age
Need to adjust Teff scale @ low [Fe/H] !
±1 conf. level
Ages not well-defined outside favourable parts of the HR diagram!
Takeda et al. 2007 – GCS new
Volume complete sample(solid),
corrected (dashed), Casuso & Beckman 2004 (dotted)
The ‘G dwarf problem’ is real:
When analysed from a complete, unbiased sample of stars with complete kinematical data and binary detection as well as metal abundances, the deficit of metal-poor dwarfs is TWICE as large.
Explanation: Early preenrichment,infall of gas, . . . .
Assumptions in classical chemical evolution models:
Reddened F giants (over-corrected?)
Full magnitude-limited sample : 7,566 stars with ’well-defined’ ages
Nordström et al. 2004
462 single FGK dwarfs
189 F dwarfs
(no) GK dwarfs
(also found for open clusters)
Volume-limited sample (d < 40 pc)
Edvardsson et al. (1993)
Challenge for model builders!
Nordström et al. local sampleShaver 1983; Fitch&Silkey 1991;
Vilchez & Esteban 1996
New models by Schönrich Binney (2008)
age < 25%
7,237 single stars with ”well-defined” ages and all data
Freeman : Velocity dispersion of nearby F
stars saturates after 2 Gyr (data from E93)
saturation seen for ages > 2 Gyr !
(galaxy mergers traceable)
age < 25%
Hard to distinguish between initial conditions & evolution
biased samples & oversimplified assumptions
”Dynamical streams” identified by Famaey et al. (2005), large sample of K & M giants
How to distinguish these dynamical features from the substructure due to past mergers?
Chemical tagging = elemental abundances
Our local sampleShaver 1983; Fitch&Silkey 1991;
Vilchez & Esteban 1996
Long-lived stars near the sun
Zn: Trace element in Universe
25M 20M 13M
Zn does not bind to dust grains and is therefore a measure of the
metal content in interstellar gas. But the relative production of Zn
is largest in the earliest and/or most massive stars.
- Spectroscopy (elemental abundances)
- Radial velocities, parallaxes, etc.