1. Chapter 16 – Chemical Analysis
Review of curves of growth
The linear part:
The width is set by the thermal width
Eqw is proportional to abundance
The “flat” part:
The central depth approaches its maximum value
Line strength grows asymptotically towards a constant value
The “damping” part:
Line width and strength depends on the damping constant
The line opacity in the wings is significant compared to kn
Line strength depends (approximately) on the square root of the abundance
How does line strength depend on excitation potential, ionization potential, atmospheric parameters (temperature and gravity), microturbulence
Differential Analysis
Fine Analysis
Spectrum Synthesis

2. Determining Abundances
Classical curve of growth analysis
Fine analysis or detailed analysis
computes a curve of growth for each individual line using a model atmosphere
Differential analysis
Derive abundances from one star only relative to another star
Usually differential to the Sun
gf values not needed – use solar equivalent widths and a solar model to derive gf values
Spectrum synthesis
Uses model atmosphere, line data to compute the spectrum

3. Jargon [m/H] = log N(m)/N(H)star – log N(m)/N(H)Sun
[Fe/H] = -1.0 is the same as 1/10 solar
[Fe/H] = -2.0 is the same as 1/100 solar
[m/Fe] = log N(m)/N(Fe)star – log N(m)/N(Fe)Sun
[Ca/Fe] = +0.3 means twice the number of Ca atoms per Fe atom

4. Solar Abundances from Grevesse and Sauval

5. Basic Methodology for “Solar-Type” Stars
Determine initial stellar parameters
Composition
Effective temperature
Surface gravity
Microturbulence
Derive an abundance from each line measured using fine analysis
Determine the dependence of the derived abundances on
Excitation potential – adjust temperature
Line strength – adjust microturbulence
Ionization state – adjust surface gravity

6. Using stellar Fe I lines to determine model atmosphere parameters
derived abundance should not depend on line strength, excitation potential, or wavelength.
If the model and atomic data are correct, all lines should give the same abundance

7. Adjusting for Excitation Potential
For weak lines on the linear part of the COG, curves of growth can be shifted along the abcissa until they line up, using the difference in excitation potential
If the temperature is right, all the curves will coincide
Dlog A = log (gf/g’f) + log l/l’ – log kn/kl – qex(c – c’)

8. Using a good model
The temperature distribution of the model - the T(t) relation, can make a difference in the shape of the COG
The differences depend on excitation potential because the depth of formation depends on excitation potential

9. The COG for Fe II lines depends on gravity
Fe II lines can be used to determine the gravity
The iron abundance from Fe II lines must also match the iron abundance from Fe I lines

10. Strong lines
Strong lines are sensitive to gravity and to microturbulence
The microturbulence in the Sun is typically 0.5 km s-1 at the center of the disk, and 1.0 km s-1 for the full disk
For giants, the microturbulence is typically 2-3 km s-1

11. Compute the line profile to match the observed spectrum
Spectrum Synthesis
Compute the line profile to match the observed spectrum
Vary the abundance to get a good fit.
Jacobson et al. determination of the sodium abundance in an open cluster giant
Model profiles are shown for 3 different oxygen abundances

12. Spectrum Synthesis II (Jacobson)
[O I]
Oxygen abundance determinations
Matching the line profile for 3 different values of the oxygen abundance, with D[O/H] = 0.5 dex
Note CN lines also present near the [O I] line. The strength of CN also depends on the oxygen abundance
When O is low, CN is stronger… Why?

13. Interesting Problems in Stellar Abundances
Precision Abundances
Solar iron abundance
Effects of 3D hydro
Solar analogs
Stellar Populations
SFH of the Galactic thin/thick disk
Population diagnostics
Migrating stars
Merger remnants
Dwarf spheroidals
Galactic Bulge
Nucleosynthesis
Abundance anomalies in GC
Extremely metal poor stars
Peculiar red giant stars
Metallicity and Planets
Evidence for mixing and diffusion

14. Planets and Metallicity
Fisher & Valenti 2005
Planets and Metallicity
What does this tell us about planet formation?
What about 2nd order effects (O/Fe, Mg/Fe, Ca/Fe)???

15. Iron in the Solar Neighborhood
Why Iron?
Fe is abundant
Fe is easy
Fe is made in
supernovae
[Fe/H] is not a good indicator of the age of the disk

16. Ultra Metal-Poor Stars
Science Magazine
Ultra Metal-Poor Stars
Ultra metal-poor stars are rare in the halo
Most metal poor star known is ~ [Fe/H] = -6
Surveys use Ca II K line

17. Alpha-process Elements:
Excesses at low metallicity
a/Fe ratio originally set by SN II production
Later, SN Ia produce a different Ca/Fe ratio
Edvardsson et al.
Pilachowski et al.
McWilliam et al.

18. How to Make Heavy Metals: neutron-capture processes
Main s-process
Low mass stars
Double shell burning
Makes SrYZr, Ba,
etc.
r-process
High neutron flux
Type II Supernovae (massive stars)
No time for b-decay
Eu, Gd, Dy, some Sr, Y, Zr, Ba, La…
s-process
Low neutron flux
B-decay before next n-capture
No Eu, Gd, Dy
Weak s-process
Massive stars
He-core and shell
Burning
Lower neutron flux
makes SrYZr only

19. n-capture Synthesis Paths
138
139 La p
s,r
130
132
134
135
136
137
138 Ba p p s
s,r s
s,r
s,r
133 Cs
s,r
128
129
130
131
132
134
136 Xe s
s,r s
s,r
s,r r r
s-process path
r-process path

20. r- and s-Process Elements

21. Heavy Metal Abundances
Note:
Scatter
Deficiencies at low metallicity
Excesses at intermediate metallicity

22. r-Process vs. s-Process
Transition from
r-process only
to r+s process
at loge(Ba)=+0.5
Corresponds to
[Fe/H] ~ -2.5
S-process
nucleosynthesis
begins to contribute
to galactic chemical
enrichment
At lower metallicities
only r-process
contributes

23. n-capture Abundances in BD+17o3248
Scaled solar-system r-process curve: Sneden 2002

24. Solar-System s-process Abundances DON’T Fit
Sneden (2002), Burris et al. (2000)

25. BD +17 3248 Is Typical of Very Metal Poor Stars
Sneden et al. (2000); Westin et al. (2000); Cowan et al. (2002)

26. Abundance Dispersions in Globular Clusters
Christian!!

27. Star Formation History in DSps
CMD for the Carina dwarf spheroidal galaxy from Smecker-Hane
Note at least two epochs of star formation
Abundance differences?

28. SFH in Omega Centauri
Pancino et al. 2000
Lee et al 1999, Nature 402, 55
The globular cluster Omega Cen also shows interesting structure in its CMD indicating multiple epochs of star formation
Epochs of star formation reflected in metallicity distribution function