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Analysis and Interpretation of Astronomical Spectra 5
20.5 Experiments with the Balmer-Decrement ................................................................................... 95
21 Spectroscopic Determination of Interstellar Extinction....................................96
21.1 Spectroscopic Definition of the Interstellar Extinction .............................................................. 96
21.2 Extinction Correction with the Measured Balmer-Decrement .................................................. 96
21.3 Balmer-Decrement and Color Excess .......................................................................................... 97
21.4 Balmer-Decrement and Extinction Correction in the Amateur Sector ...................................... 97
22 Plasma Diagnostics for Emission Nebulae .........................................................98
22.1 Preliminary Remarks ..................................................................................................................... 98
22.2 Overview of the Phenomenon “Emission Nebulae”.................................................................... 98
22.3 Common Spectral Characteristics of Emission Nebulae............................................................ 98
22.4 Ionisation Processes in H II Emission Nebulae ........................................................................... 98
22.5 Recombination Process ................................................................................................................ 99
22.6 Line Emission by Electron Transition ........................................................................................... 99
22.7 Line Emission by Collision Excitation.........................................................................................100
22.8 Line Emission by Permitted Transitions (Direct absorption)....................................................100
22.9 Line Emission by Forbidden Transitions ....................................................................................100
22.10 Scheme of the Photon Conversion Process in Emission Nebulae...........................................102
22.11 Practical Aspects of Plasma Diagnostics ..................................................................................103
22.12 Determination of the Excitation Class ....................................................................................104
22.13 The Excitation Class as an Indicator for Plasma Diagnostics ..................................................104
22.14 Estimation of Te and Ne with the O III and N II Method...........................................................105
22.15 Estimation of the Electron Density from the S II and O II Ratio ...............................................106
22.16 Distinguishing Characteristics in the Spectra of Emission Nebulae .......................................106
23 Analysis of the Chemical Composition ............................................................ 108
23.1 Astrophysical Definition of Element Abundance ......................................................................108
23.2 Astrophysical Definition of Metal Abundance Z (Metallicity) ..................................................108
23.3 Quantitative Determination of the Chemical Composition ......................................................108
23.4 Relative Abundance-Comparison at Stars of Similar Spectral Class ......................................109
24 Spectroscopic Parallax ...................................................................................... 110
24.1 Spectroscopic Possibilities of Distance Measurement ............................................................110
24.2 Term and Principle of Spectroscopic Parallax ..........................................................................110
24.3 Spectral Class and Absolute Magnitude ...................................................................................110
24.4 Distance Modulus........................................................................................................................112
24.5 Calculation of the Distance with the Distance Modulus..........................................................112
24.6 Examples for Main Sequence Stars (with Literature Values) ..................................................112
25 Identification of Spectral Lines......................................................................... 113
25.1 Task and Requirements ..............................................................................................................113
25.2 Practical Problems and Solving Strategies ...............................................................................113
25.3 Tools for the Identification of Spectral Lines ............................................................................114
26 Literature and Internet....................................................................................... 115
