Book contents
- Frontmatter
- Contents
- Preface to the first edition
- Preface to the second edition
- Preface to the third edition
- 1 Background
- 2 Fourier transforms
- 3 Spectroscopic tools
- 4 Light detectors
- 5 Radiation terms and definitions
- 6 The black body and its radiation
- 7 Radiative and convective energy transport
- 8 The continuous absorption coefficient
- 9 The model photosphere
- 10 The measurement of stellar continua
- 11 The line absorption coefficient
- 12 The measurement of spectral lines
- 13 The behavior of spectral lines
- 14 The measurement of stellar radii and temperatures
- 15 The measurement of photospheric pressure
- 16 Chemical analysis
- 17 Velocity fields in stellar photospheres
- 18 Stellar rotation
- Appendix A A table of useful constants
- Appendix B Physical parameters of stars
- Appendix C A fast Fourier transform Fortran program
- Appendix D Atomic data
- Appendix E The strongest lines in the solar spectrum
- Appendix F Computation of random errors
- Index
- References
16 - Chemical analysis
Published online by Cambridge University Press: 05 March 2015
- Frontmatter
- Contents
- Preface to the first edition
- Preface to the second edition
- Preface to the third edition
- 1 Background
- 2 Fourier transforms
- 3 Spectroscopic tools
- 4 Light detectors
- 5 Radiation terms and definitions
- 6 The black body and its radiation
- 7 Radiative and convective energy transport
- 8 The continuous absorption coefficient
- 9 The model photosphere
- 10 The measurement of stellar continua
- 11 The line absorption coefficient
- 12 The measurement of spectral lines
- 13 The behavior of spectral lines
- 14 The measurement of stellar radii and temperatures
- 15 The measurement of photospheric pressure
- 16 Chemical analysis
- 17 Velocity fields in stellar photospheres
- 18 Stellar rotation
- Appendix A A table of useful constants
- Appendix B Physical parameters of stars
- Appendix C A fast Fourier transform Fortran program
- Appendix D Atomic data
- Appendix E The strongest lines in the solar spectrum
- Appendix F Computation of random errors
- Index
- References
Summary
When we look at stellar spectra, we soon recognize the presence of many chemicals. The lines of hydrogen dominate the photospheric spectra of hot stars, but with declining temperature, thousands of lines from other species grow stronger while the lines of hydrogen weaken. One of the tasks of the stellarphotosphere analyst is to disentangle the effects of temperature, pressure, turbulence, and so on from the effects of chemical composition. In broad strokes, the results of chemical analyses tell us that hydrogen is overwhelmingly the most abundant element, comprising ≈90% of the atoms in a normal stellar photosphere, and helium comes next with ≈10%. The remaining elements, often referred to as “metals,” comprise a sprinkling – like salt in a bowl of broth – adding savor and interest. Most of the spectral lines are caused by these low-abundance elements.
Besides our natural curiosity to know what stars are made of, we are motivated to perform chemical composition studies on other fronts. To be more specific, almost any study in stellar atmospheres presupposes some chemical composition. Chemical evidence tells us about the nuclear reactions taking place in stars, internal mixing of material, penetration depths of convection zones, diffusion and gravitational settling, or accretion of material from interstellar space. Lithium and carbon isotope abundances are signatures of the evolutionary stage of a star. The evolution of our galaxy is traceable in part through the differences in chemical composition among stars, since we expect stars formed at different times and in different places to retain information concerning the composition of the material from which they formed.
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- Information
- The Observation and Analysis of Stellar Photospheres , pp. 384 - 422Publisher: Cambridge University PressPrint publication year: 2005