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

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