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5-Evidence of abundances from spectral lines (Voigt profile and curve of…
5-Evidence of abundances from spectral lines
Doppler and natural comparison
figures
as N increases strong damping wings dominate absorption line (for natural)
(for doppler) basic gaussian shape is kept
Voigt profile and curve of growth
Consider smooth continuum spectrum passing through uniform gaseous column that absorbs light at preferential wavelengths
At moderate optical depths only doppler is significant
line said to be optically thin
higher optical depths
gaussian profile 'bottoms out'
optically thick
slower variation
very high optical depths
lorentzian damping becomes dominant
combination of profiles results in voigt
Curve of Growth
line width increase with column density
Extracting chemical abundances
Using the curve of growth along with boltzmann and saha can hive total number of atoms of element lying above the photosphere
Boltzmann
different excitation levels
Saha
different ionisation states
Maths:
Solar and local galactic abundances
photometric absorption line give much information
Emission lines from solar chromosphere, prominences and corona
radioactive decays taken into account
meteorite composition in good agreement with solar ab lines espec. CC
Local abundance curve typical for nearby stars and ISM
Abundance variations
Outside solar system
factors
point in stars evolution
mixing of surface layers
Chemically peculiar (CP) stars
caused gravitational settling or radiative levitation from magnetic fields
Population effects
pop 1-young, circular orbits close to plane of galax, low v, metal rich
pop 2 - old, in galactic halo, elongated/inclined orbits, high velocities, metal poor