Download Determining Abundances

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
• Spectrum synthesis
– Uses model atmosphere, line data to
compute the spectrum
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
Solar Abundances from
Grevesse and Sauval
CNO
Log e (H=12)
8
Fe
5
Sr, Y, Zr
Sc
2
Ba
Li, Be, B
Eu
-1
10
20
30
40
50
Atomic Number
60
70
80
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
Projects!
• Derive the composition of Arcturus from
high resolution infrared spectra. Compare
results to optical determinations.
– Adopt the published model atmosphere
parameters
– Use the Hinkle et al. atlas to measure
equivalent widths
– Derive gf values from the solar spectrum
Project II
• Derive the composition of one (or two
or three) giants in the globular
cluster M3 from high resolution IR
Keck/NIRSPEC spectra
– Differential analysis relative to
Arcturus
– Use published model atmosphere
parameters
Project III
• Derive model atmosphere parameters
from measured equivalent widths for
the G8 III giant Epsilon Virginis
• Use laboratory gf’s
Project IV
• Derive spectroscopic atmospheric
parameters for the Sun from
measured equivalent widths and
published laboratory gf values
• Determine the solar iron abundance
from Fe I and Fe II lines
Project V
• Determine atmospheric parameters
for a metal-poor giant or subgiant
from measured equivalent widths and
laboratory gf-values