Analysis and Interpretation of Astronomical Spectra Analysis and Interpretation of Astronomical Spectra Theoretical Background and Practical Applications for Amateur Astronomers Richard Walker Version 9.2 12/2013 Analysis and Interpretation of Astronomical Spectra Table of Contents Introduction Photons – Messengers from the Universe 2.1 2.2 2.3 2.4 2.5 Photons – Carriers of Information The Duality of Waves and Particles The Quantisation of the Electromagnetic Radiation Properties of the Photons Photons – Carriers of Energy The Continuum 10 3.1 3.2 3.3 Black Body Radiation and the Course of the Continuum Level 10 Plank's Radiation- and Wien's Displacement Law 10 The Pseudo Continuum 11 Spectroscopic Wavelength Domains 13 4.1 4.2 4.3 The Usable Spectral Range for Amateurs 13 The Selection of the Spectral Range 13 Terminology of the Spectroscopic Wavelength Domains 14 Typology of the Spectra 15 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 Continuous Spectrum 15 Absorption Spectrum 15 Emission Spectrum 15 Absorption Band Spectrum 16 Band Spectrum with Inversely Running Intensity Gradient 16 Mixed Emission- and Absorption Spectrum 17 Composite Spectrum 17 Reflectance Spectrum 18 Cometary Spectrum 18 Form and Intensity of the Spectral Lines 19 6.1 6.2 6.3 6.4 6.5 The Form of the Spectral Line 19 The Information Content of the Line Shape 19 Blends 19 The Saturation of an Absorption Line in the Spectral Diagram 19 The Oversaturated Emission Line in the Spectral Diagram 20 The Measurement of the Spectral Lines .21 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 7.10 7.11 Methods and Reference Values of the Intensity Measurement 21 Metrological Differences between Absorption and Emission Lines 21 The Peak Intensity P 22 Full Width at Half Maximum Height 22 , Equivalent Width 23 Normalised Equivalent Width 24 FWZI Full Width at Zero Intensity 24 Influence of the Spectrograph Resolution on the FWHM- and EW Values 24 Practical Consequences for the FWHM and EW Measurements 26 The Measurement of the Wavelength 26 Additional Measurement Options 26 Analysis and Interpretation of Astronomical Spectra Calibration, Normalisation and Radiometric Correction 27 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 8.9 8.10 8.11 8.12 8.13 8.14 8.15 The Calibration of the Wavelength 27 The Selective Attenuation of the Continuum Intensity 27 Relationship Between Original-Continuum and Pseudo-Continuum 28 Attenuation of Absorption Lines 28 Attenuation of the Emission Lines 29 Summary of the consequences: 30 The Importance of the Pseudo-Continuum 30 Proportional Radiometric Corrections of the Pseudo-Continuum 30 Rectification of the Continuum Intensity 31 Relative Radiometric Flux Calibration by a Synthetic Continuum 32 Relative Radiometric Profile Correction by Recorded Standard Stars 35 Absolute Flux Calibration 37 Intensity Comparison between Different Spectral Lines 37 Reconstruction of the Original Emission-Line Intensities 37 Summary – Which Method Fits to Which Task 38 Visible Effects of Quantum Mechanics .39 9.1 9.2 9.3 Textbook Example Hydrogen Atom and Balmer Series 39 The Balmer Series 40 Spectral Lines of Other Atoms 41 10 Wavelength and Energy .42 10.1 10.2 10.3 10.4 Planck’s Energy Equation 42 Units for Energy and Wavelength 42 The Photon Energy of the Balmer Series 43 Balmer- Paschen- and Bracket Continuum 44 11 Ionisation Stage and Degree of Ionisation 45 11.1 11.2 11.3 The Lyman Limit of Hydrogen 45 Ionisation Stage versus Degree of Ionisation 45 Astrophysical Form of Notation for the Ionisation Stage 45 12 Forbidden Lines or –Transitions 46 13 The Spectral Classes 47 13.1 13.2 13.3 13.4 13.5 13.6 13.7 13.8 13.9 13.10 13.11 13.12 13.13 Preliminary Remarks 47 The Fraunhofer Lines 47 Further Development Steps 48 The Harvard System 49 “Early” and “Late” Spectral Types 50 The MK (Morgan Keenan) or Yerkes System 50 Further Adaptations up to the Present 50 The Rough Estimation of the Spectral Class 52 Diagrams for Estimation of the Spectral Class 53 Additional Criteria for Estimation of the Spectral Class 54 Appearance of Elements, Ions and Molecules in the Spectra 55 Effect of the Luminosity Class on the Line Width 56 Spectral Class and B-V Colour-Index 56 14 The Hertzsprung - Russell Diagram (HRD) 57 14.1 14.2 Introduction to the Basic Version 57 The Absolute Magnitude and Photospheric Temperature of the Star 58 Analysis and Interpretation of Astronomical Spectra 14.3 14.4 14.5 14.6 The Evolution of the Sun in the HRD 59 The Evolution of Massive Stars 60 The Relation between Stellar Mass and Life Expectancy 60 Age Estimation of Star Clusters 61 15 The Measurement of the Radial Velocity 62 15.1 15.2 15.3 15.4 15.5 15.6 15.7 15.8 15.9 15.10 15.11 15.12 15.13 The Radial Velocity 62 The Classical Doppler Effect 62 The z-Value - A Fundamental Measure of Modern Cosmology 63 The Relativistic Doppler Effect for Electromagnetic Waves 64 The Measurement of the Doppler Shift 64 Radial Velocities of Nearby Stars 65 Relative Shift within a Spectrum caused by the Doppler Effect 65 Radial Velocities of Galaxies 65 The Apparent Dilemma at 66 Radial Velocity- and Cosmological Spacetime Expansion at Messier-Galaxies 66 The Redshift of the Quasar 3C273 68 The Gravitational Redshift 69 Short Excursus on "Hubble time" tH 69 16 The Measurement of the Rotation Velocity 70 16.1 16.2 16.3 16.4 16.5 16.6 16.7 Terms and Definitions 70 The Rotation Velocity of the Large Planets 70 The Rotation Velocity of the Sun 71 The Rotation Velocity of Galaxies 71 Calculation of the Value with the Velocity Difference 71 The Rotation Velocity of the Stars 73 The Rotation Velocity of the Circumstellar Disks around Be Stars 75 17 The Measurement of the Expansion Velocity .79 17.1 17.2 17.3 17.4 P Cygni Profiles 79 Inverse P Cygni Profiles 79 Broadening of the Emission Lines 80 Splitting of the Emission Lines 80 18 The Measurement of the Stellar Photosphere Temperature 81 18.1 18.2 18.3 18.4 18.5 Introduction 81 Temperature Estimation of the Spectral Class 81 Temperature Estimation Applying Wien’s Displacement Law 82 Temperature Determination Based on Individual Lines 85 The “Balmer-Thermometer“ 85 19 Spectroscopic Binary Stars 87 19.1 19.2 19.3 19.4 Terms and Definitions 87 Effects of the Binary Orbit on the Spectrum 88 The Perspectivic Influence from the Spatial Orientation of the Orbit 90 The Estimation of some Orbital Parameters 91 20 Balmer–Decrement .93 20.1 20.2 20.3 20.4 Introduction 93 Qualitative Analysis 93 Quantitative Analysis 94 Quantitative Definition of the Balmer-Decrement 95 Analysis and Interpretation of Astronomical Spectra 20.5 Experiments with the Balmer-Decrement 95 21 Spectroscopic Determination of Interstellar Extinction 96 21.1 21.2 21.3 21.4 Spectroscopic Definition of the Interstellar Extinction 96 Extinction Correction with the Measured Balmer-Decrement 96 Balmer-Decrement and Color Excess 97 Balmer-Decrement and Extinction Correction in the Amateur Sector 97 22 Plasma Diagnostics for Emission Nebulae 98 22.1 22.2 22.3 22.4 22.5 22.6 22.7 22.8 22.9 22.10 22.11 22.12 22.13 22.14 22.15 22.16 Preliminary Remarks 98 Overview of the Phenomenon “Emission Nebulae” 98 Common Spectral Characteristics of Emission Nebulae 98 Ionisation Processes in H II Emission Nebulae 98 Recombination Process 99 Line Emission by Electron Transition 99 Line Emission by Collision Excitation 100 Line Emission by Permitted Transitions (Direct absorption) 100 Line Emission by Forbidden Transitions 100 Scheme of the Photon Conversion Process in Emission Nebulae 102 Practical Aspects of Plasma Diagnostics 103 Determination of the Excitation Class 104 The Excitation Class as an Indicator for Plasma Diagnostics 104 Estimation of Te and Ne with the O III and N II Method 105 Estimation of the Electron Density from the S II and O II Ratio 106 Distinguishing Characteristics in the Spectra of Emission Nebulae 106 23 Analysis of the Chemical Composition 108 23.1 23.2 23.3 23.4 Astrophysical Definition of Element Abundance 108 Astrophysical Definition of Metal Abundance Z (Metallicity) 108 Quantitative Determination of the Chemical Composition 108 Relative Abundance-Comparison at Stars of Similar Spectral Class 109 24 Spectroscopic Parallax 110 24.1 24.2 24.3 24.4 24.5 24.6 Spectroscopic Possibilities of Distance Measurement 110 Term and Principle of Spectroscopic Parallax 110 Spectral Class and Absolute Magnitude 110 Distance Modulus 112 Calculation of the Distance with the Distance Modulus 112 Examples for Main Sequence Stars (with Literature Values) 112 25 Identification of Spectral Lines 113 25.1 25.2 25.3 Task and Requirements 113 Practical Problems and Solving Strategies 113 Tools for the Identification of Spectral Lines 114 26 Literature and Internet 115 Analysis and Interpretation of Astronomical Spectra Change log of the Document Versions Version 8.0: Sect 5.9: New: “Cometary Spectra“ Sect 6.4: Supplement Sect 10.4: New: “Balmer- Paschen- and Bracket Continuum” Sect 18: New: “The Measurement of the Stellar Photosphere Temperature“ Sect 23: New: “Chemical Composition Analysis“ Sect 24: New: “Spectroscopic Parallax” Versions 8.5 and 8.6: Sect 8: General revision “Calibration and Normalisation of Spectra” in consideration of recent test results on "correction curves” Version 8.7: Sect 15.7: Review and corrections in the table of Messier galaxies and appropriate adjustments in the text Version 9.0: Sect 8: General revision: Consideration of the different attenuation-behavior of absorptionversus emission lines, in relation to the continuum-intensity Sect 13: New Subtitles, 13.10, 13.11 and 13.13 with new table: Spectral Class and B-V Colour-Index Sect 15: General revision: Derivation of the classical and relativistic, spectroscopic Doppler formula Several corrections and supplements, particularly in sect 15.8 Radial Velocities of Galaxies New: sect 15.12: Gravitational Redshift Sect 16.3: Supplement of the Sun's rotation with spectral profile and measurement results by SQUES Echelle Spectrograph Sect 17.1: Supplement of literature reference Sect 18: Content of former sect 18.6, now integrated in 18.4 Sect 20, 21, 22: Various modifications and additions due to the general revision of sect Literature and Internet: New entries Analysis and Interpretation of Astronomical Spectra Introduction Technological advances like CCD cameras, but also affordable spectrographs on the market, actually cause a significant upturn of spectroscopy within the community of amateur astronomers Further freeware programs and detailed instructions are available to enable the processing, calibrating and normalising of the spectra Several publications explain the function and even the self-construction of spectrographs and further many papers can be found on specific monitoring projects The numerous possibilities however for analysis and interpretation of the spectral profiles, still suffer from a considerable deficit of suitable literature This publication is intended as an introduction to practical applications and the appropriate astrophysical backgrounds Further the Spectroscopic Atlas for Amateur Astronomers [33] is available, which covers all relevant spectral classes by commenting most of the lines, visible in medium resolved spectral profiles It is primarily intended to be used as a tool for the line identification Each spectral class, relevant for amateurs, is presented with their main characteristics and typical features Further, Practical Aspects of Astro-Spectroscopy – Instructions and Information for Amateur Astronomers [30], is downloadable It provides detailed instructions for operational aspects and data reduction of spectral profiles with the Vspec and IRIS software Spectroscopy is the real key to astrophysics Without them, our current picture of the universe would be unthinkable The photons, which have been several million years “on the road” to our CCD cameras, provide an amazing wealth of information about the origin object This may be fascinating, even without the ambition to strive for academic laurels Further there is no need for a degree in physics with, specialisation in mathematics, for a rewarding deal with this matter Required is some basic knowledge in physics, the ability to calculate simple formulas with given numbers on a technical calculator and finally a healthy dose of enthusiasm Even the necessary chemical knowledge remains very limited In the hot stellar atmospheres and excited nebulae the individual elements can hardly undergo any chemical compounds Only in the outermost layers of relatively "cool" stars, some very simple molecules can survive More complex chemical compounds are found only in really cold dust clouds of the interstellar space and in planetary atmospheres – a typical domain of radio astronomy Moreover in stellar astronomy, all elements, except hydrogen and helium, are simplistically called as "metals" The share of hydrogen and helium of the visible matter in the universe is still about 99% The most "metals", have been formed long time after the Big Bang within the first generation of massive stars, which distributed it at the end of their live in to the surrounding space by Supernova explosions or repelled by Planetary Nebulae Much more complex, however, is the quantum-mechanically induced behavior of the excited atoms in stellar atmospheres These effects are directly responsible for the formation and shape of the spectral lines Anyway for the practical work of the "average amateur" some basic knowledge is sufficient Richard Walker, CH 8911-Rifferswil © richiwalker@bluewin.ch Analysis and Interpretation of Astronomical Spectra Photons – Messengers from the Universe 2.1 Photons – Carriers of Information Photons are generated in stars, carrying valuable information over immense periods of time and unimaginable distances, and finally end in the pixel field of our CCD cameras By their “destruction” they deposit the valuable information, contributing electrons to the selective saturation of individual pixels – in fact trivial, but somehow still fascinating By switching a spectrograph between the telescope and camera the photons will provide a wealth of information which surpasses by far the simple photographic image of the object It is therefore worthwhile to make some considerations about this absolutely most important link in the chain of transmission It was on the threshold of the 20th Century, when it caused tremendous "headaches" to the entire community of former top physicists This intellectual "show of strength" finally culminated in the development of quantum mechanics The list of participants reads substantially like the Who's Who of physics at the beginning of the 20th century: Werner Heisenberg, Albert Einstein, Erwin Schrödinger, Max Born, Wolfgang Pauli, Niels Bohr, just to name a few Quantum mechanics became, besides the theory of relativity, the second revolutionary theory of the 20th Century For the rough understanding about the formation of the photons and finally of the spectra, the necessary knowledge is reduced to some key points of this theory 2.2 The Duality of Waves and Particles Electromagnetic radiation has both wave and particle nature This principle applies to the entire spectrum Starting with the long radio waves, it remains valid on the domains of infrared radiation, visible light, up to the extremely short-wave ultraviolet, X-rays and gamma rays Source: Wikipedia For our present technical applications, both properties are indispensable For the entire telecommunications, radio, TV, mobile telephony, as well as the radar and the microwave grill it's the wave character The CCD photography, light meter of cameras, gas discharge lamps (eg energy saving light bulbs and street lighting), and last but not least, the spectroscopy would not work without the particle nature 2.3 The Quantisation of the Electromagnetic Radiation It was one of the pioneering discoveries of quantum mechanics that electromagnetic radiation is not emitted continuously but rather quantised (or quasi "clocked") Simplified ex- Analysis and Interpretation of Astronomical Spectra plained a minimum "dose" of electromagnetic radiation is generated, called “photon”, which belongs to the Bosons within the "zoo" of elementary particles 2.4 Properties of the Photons – Without external influence photons have an infinitely long life – Their production and “destruction” takes place in a variety of physical processes Relevant for the spectroscopy are electron transitions between different atomic orbital (details see later) – A photon always moves with light speed According to the Special Theory of Relativity (STR) it can therefore possess no rest mass 2.5 Photons – Carriers of Energy Each photon has a specific frequency (or wavelength), which determines its energy – the higher the frequency, the higher the energy of the photon (details see sect 10.1) Analysis and Interpretation of Astronomical Spectra 10 The Continuum 3.1 Black Body Radiation and the Course of the Continuum Level The red curve, hereafter referred to as continuum level corresponds to the course of the radiation intensity or flux density, plotted over the wavelength, increasing from left to right As a fit to the blue continuum it is cleaned by any existing absorption or emission lines (blue curve) The entire area between the horizontal wavelength axis and the continuum level is called continuum [5] Continuum Level Ic Continuum Most important physical basis for the origin and course of the continuum is the so-called black body radiation The blackbody is a theoretical working model which, in that perfection, doesn’t exist in nature For most amateurs it is sufficient to know, that: – The blackbody is an ideal absorber which absorbs broadband electromagnetic radiation, regardless of the wavelength, completely and uniformly – The ideal black body represents a thermal radiation source, which emits a broad-band electromagnetic radiation, according to the Planck's radiation law, with an exclusively temperature-dependent intensity profile – Stars in most cases may simplified be considered as black-body radiators 3.2 Plank's Radiation- and Wien's Displacement Law This theory has practical relevance for us because the intensity profile of the spectrum provides information about the temperature of the radiator! The radiation distribution of different stars shows bell-shaped curves, whose peak intensity shifts to shorter wavelength, respectively higher frequency with increasing temperature (Planck Radiation law) Intensity T=12‘000 K λmax=2415 Å T=6000 K λmax=4830 Å T=3000 K λmax=9660 Å 5000 10‘000 Wavelength [Å] 15‘000 20‘000 Analysis and Interpretation of Astronomical Spectra 107 Planetary nebulae usually pass through all 12 excitation classes, following the evolution of the central star In this regard the SNR are also a highly complex special case By very young SNR, eg the Crab Nebula (M1), dominate higher excitation classes whose levels are not homogeneously distributed within the nebula, according to the complex filament structure [231] The diagnostic line He II at λ 4686 is therefore a striking feature in some spectra of M1, see [33], Table 85 Analysis and Interpretation of Astronomical Spectra 108 23 Analysis of the Chemical Composition 23.1 Astrophysical Definition of Element Abundance In astrophysics, the abundance of an element is expressed as decadic logarithm of the amount of particles per unit volume , to that of the hydrogen , whose abundance is defined according to convention to [57], [11] The mass ratios not matter here By transforming logarithmically we directly obtain the relationship : 23.2 Astrophysical Definition of Metal Abundance Z (Metallicity) Of great importance is the ratio of iron to hydrogen This is also computed with the relative number of atoms per unit volume and not with their individual masses The metallicity in a stellar atmosphere, also called , is expressed as the decadic logarithm in relation to the sun: values, smaller than found in the atmosphere of the Sun, are considered to be metal poor and carry a negative sign (–).The existing range reaches from approximately +0.5 to –5.4 (SuW 7/2010) Fe is used here as a representative of the metals because it appears quite frequently in the spectral profile and is relatively easy to analyse 23.3 Quantitative Determination of the Chemical Composition The identified spectral lines (sect 25) of the examined object inform directly: – which elements and molecules are present – which isotopes of an element are present (restricted to some cases and to high resolution profiles) – which stages of ionisation are generated In this context the quantitative determination of the abundance can be outlined only roughly It is very complex and can’t be obtained directly from the spectrum It requires additional information, which can partly be obtained only with simulations of the stellar photosphere [11] The intensity of a spectral line is an indicator, which provides information on the frequency of a particular element However this value is influenced, inter alia, by the effective temperature , the pressure, the gravitational acceleration, as well as the macro-turbulence and the rotational speed of the stellar photosphere Furthermore also affects the degree of ionisation of the elements, which must be calculated with the socalled Saha Equation [11] These complications are impressively demonstrated in the solar spectrum Over 90% of the solar photosphere consists of hydrogen atoms with the defined abundance of Nevertheless, as a result of the too low temperature of 5800 K, the intensity of the H Balmer series remains quite modest The dominating main features of the solar spectrum, however, are the two Fraunhofer H and K lines of ionised calcium Ca II, although its abundance is just [Anders & Grevesse 1989] According to {65}, this corresponds to a ratio of From Quantum-mechanical reasons, at the solar photospheric Analysis and Interpretation of Astronomical Spectra 109 temperature of 5800 K, Ca II is an extremely effective absorber The optimum conditions for the hydrogen lines, however, are reached not until nearly 10,000 K (see sect 9.2) In the professional area the element abundance is also determined by the iterative comparison of the spectrum with simulated synthetic profiles of different chemical composition [11] 23.4 Relative Abundance-Comparison at Stars of Similar Spectral Class Equivalent width EW [Å] A simplified special case is formed by stars with similar spectral- and luminosity class and comparable rotational velocities Thus the physical parameters of the photospheres are very similar Here the equivalent widths EW of certain lines can simply be compared and thus the relative abundance differences at least qualitatively be seen In the Spectroscopic Atlas [33] this is demonstrated at the classical example of the two main-sequence stars Sirius A1Vm and Vega A0V The basic principle is the so called Curve of Growth It shows that within its unsaturated and somewhat linearly running part, the equivalent width EW of a certain spectral line of an element, behaves roughly proportional to its number of atoms within a plasma mixture Saturated line Curve of Growth Linear region Linie profile deepening Number of atoms Analysis and Interpretation of Astronomical Spectra 110 24 Spectroscopic Parallax 24.1 Spectroscopic Possibilities of Distance Measurement Distances can spectroscopically be determined either with the spectroscopic parallax or in the extragalactic range, with help of the Doppler-related redshift, combined with the Hubble’s Law (sect 15.8) These methods are supplemented by radar and laser reflectance measurements (solar system), the trigonometric parallax (closer solar neighborhood) and the photometric parallax (Milky Way and extragalactic area) The latter is based on the brightness, compared with precisely known, so-called "standard candles" as Cepheids and supernovae of type Ia 24.2 Term and Principle of Spectroscopic Parallax The spectroscopic parallax allows the rough distance-estimation to a star, based solely on the spectroscopically determined spectral class and photometrically measured, apparent brightness Therefore the term "parallax" is here a misnomer However, it is correct for the trigonometric parallax This corresponds to the apparent shift of the observed celestial body relative to the sky background, caused by the Earth's orbit around the sun The principle of spectroscopic parallax works similar to the photometric parallax The absolute magnitude of an object is generally defined for the distance of 10 parsecs [pc] or 32.6 light years [ly] This value is first compared with the actually measured, apparent brightness, enabling the calculation of the distance Applying the spectroscopic parallax, the absolute brightness of a star is determined by its spectral class 24.3 Spectral Class and Absolute Magnitude The following table shows the values of the absolute magnitudes for the main sequence stars (V) from a lecture at the University of Northern Iowa http://www.uni.edu/ Their deviation, in comparison with known literature values, remains, for our purpose, within acceptable limits For instance, the table value for the spectral class G2V does 5.0M, compared to the literature value for the sun of 4.83M For the giants (III) and supergiants (I), I have collected some literature values of known stars from different sources in order to give an impression of the magnitude and the enormous spread At these luminosity classes no usable conjunction with the spectral classes can be recognised Further supergiants of early spectral classes are often spectroscopic binaries These facts also drastically demonstrate the limitations of this method Therefore the determination of the distance, applying the spectroscopic parallax is, at least for amateurs, restricted to main-sequence stars To find In the annex to Gray/Corballi [4] is a calibration table of the absolute magnitudes for all spectraland luminosity classes of the MK System Spectral Class Main Sequence (V) O5 –4.5 O6 –4.0 O7 –3.9 O8 –3.8 O9 B0 Giants (III) Supergiants (I) Meissa, λ Ori –4.3 –3.6 Iota Ori –5.3 –3.3 Alnilam, ε Ori –6.7 B1 –2.3 Alfirk, β Cep –3.5 B2 –1.9 Bellatrix, γ Ori –2.8 ζ Ori, Alnitak –5.3 Analysis and Interpretation of Astronomical Spectra B3 –1.1 B5 –0.4 B6 B7 111 δ Per –3.0 Aludra, η Cma –7.5 0.3 Alcione, η Tau –2.5 B8 0.7 Atlas, 27 Tau –2.0 Rigel, β Ori –6.7 B9 1.1 A0 1.5 A1 1.7 A2 1.8 Deneb, α Cyg –8.7 A3 2.0 A4 2.1 A5 2.2 A7 2.4 γ Boo, F0 3.0 Adhafera, ζ Leo F2 3.3 Caph, β Cas F3 3.5 F5 3.7 Mirfak, α Per –4.5 F6 4.0 F7 4.3 F8 4.4 Wezen, δ CMa –6.9 G0 4.7 Sadalsuud, β Aqr –3.3 G1 4.9 G2 5.0 Sadalmelik, α Aqr –3.9 G5 5.2 Antares, α Sco –5.3 Betelgeuse, α Ori –5.3 Ras Algethi, α Her –2.3 G7 α Oph, 1.2 1.0 –1.0 1.2 Kornephoros, β Her –0.5 G8 5.6 Vindemiatrix, ε Vir K0 6.0 Dubhe, α Uma K1 6.2 K2 6.4 K3 6.7 K4 7.1 K5 7.4 Aldebaran, α Tau K7 8.1 Alsciaukat, α Lyn –1.1 M0 8.7 M1 9.4 Scheat, β Peg –1.5 M2 10.1 M3 10.7 M4 11.2 M5 12.3 M6 13.4 M7 13.9 M8 14.4 Cebalrai, β Oph 0.4 –1.1 0.8 –0.7 Analysis and Interpretation of Astronomical Spectra 112 24.4 Distance Modulus The distance modulus is defined by the difference between the apparent- [m] and absolute magnitude [M], expressed in the generally used, logarithmic system of the photometric brightness levels [mag] In contrast to the Apparent Distance Modulus , the so called True Distance Modulus applies to the simplified calculation, assuming no Interstellar Extinction, [12] 24.5 Calculation of the Distance with the Distance Modulus Assuming no Interstellar Extinction, the relationship between the distance True Distance Modulus can be expressed as: If the interstellar extinction is considered, ( must still be added: average interstellar extinction By logarithmic transforming and the can be expressed explicitly: According to [12] in worst case, ie within the galactic plane, results If dark clouds are located on the line of sight, may rise up to to Further it becomes recognisable, that the extinction starts normally to be noticable not until about 100 pc Anyway [58] proposes the rule of thumb to take for the solar neighborhood The problem here is that depends also on the desired distance {69} 24.6 Examples for Main Sequence Stars (with Literature Values) Sirius, α Cma A1Vm m=–1.46 M=1.43 r = 2.64 pc = 8.6 Lj Denebola, β Leo A3V m= 2.14 M=1.93 r = 11.0 pc = 36 Lj 61 Cyg A, K5 m= 5.21 M= 7.5 r = 3.5 pc = 11 Lj Analysis and Interpretation of Astronomical Spectra 113 25 Identification of Spectral Lines 25.1 Task and Requirements With the line identification, to an absorption- or emission line with the wavelength , the responsible element or ion is assigned Considered purely theoretical this would have to be relatively simple, as shown by the adjoining excerpt of the "lineident" table, provided by the Vspec software In practice, however, inter alia the following should be noted: – The spectrum must show a high S/N ratio, further be calibrated very precisely and adjusted by possible Doppler shifts Only that way we can exactly determine the wavelength of each line – The higher the resolution of the spectrum, the more accurate can be determined and the fewer lines are merging into so-called “Blends” 25.2 Practical Problems and Solving Strategies However the table shows, that in certain sections of the spectrum, the distances between the individual positions are obviously very close This happens from quantum mechanical reasons for several of the metal lines, generating corresponding ambiguities, especially in stellar spectra of the medium and later spectral classes Commonly concerned are also noble gases, as well as the so-called rare earth compounds – eg praseodymium, lanthanum, yttrium etc Such we find in the spectra of gas-discharge lamps, acting here as dopants, alloy components and fluorescent agents Here, in most of the cases, helps the process of elimination Most important is the knowledge of the involved process temperature For stellar spectra it is supplied by the according spectral class With this parameter the graphic at the end of sect 13.11, provides on one hand possible proposals, but excludes a priori also certain elements or corresponding ionisation stages As there already discussed, eg for normal photospheric solar spectra, Helium He I can be excluded At certain stages of stellar evolution, detailed knowledge of the involved processes are necessary Since e.g stars, in the final Wolf Rayet stage, first of all repel their entire outer hydrogen shell, this element can therefore subsequently hardly be detected in such spectra Critical is here the mostly very significant He II emission at 6560.1 Å, which is often misinterpreted by amateurs as Hα line at 6562.82 Å, see [33] tables and Relatively easy is the line identification for calibration lamps with known gas filling Thus Vspec allows the superimposing of the corresponding emission lines, with their relative intensities, directly into the calibrated lamp spectrum (see below) For such "laboratory spectra" in Vspec [411] the "element" database has proven (Tools/Elements/element) For stellar profiles, however, the "lineident" database is to prefer (Tools/Elements/lineident) In cases of unknown gas filling, on a trial basis, the emission lines of the individual noble gases He, Ne, Ar, Kr and Xe can be superimposed to the calibrated Lamp spectrum In most cases already the pattern of these inserted lines instantly shows, if the corresponding element is present or not This was also the most successful tactic for the line identification in [32] [33] [34] [35] However some of the noble gas emissions can be located very close to each other such as Ar 6114.92 Å and Xe 6115.08 Å, see [33] Table 102 Analysis and Interpretation of Astronomical Spectra 114 25.3 Tools for the Identification of Spectral Lines For stellar spectra, a spectral atlas is probably the safest way to identify spectral lines (see bibliography) For rare stellar types, object related publications are often very helpful The software solutions based on model spectra are primarily used in the professional astronomy and are hardly suitable for most amateurs For a detailed analysis of individual elements and their ions also online databases are available, such as from the U.S American NIST (National Institute of Standards and Technology) [103] The following screenshot shows the calibrated Vspec DADOS spectrum [401] of the Wolf Rayet star WR 136, with the superimposed He II emission lines from the "lineident" database For a commented spectrum refer to [33], Table This Vspec screenshot shows a high-resolution Echelle SQUES spectrum [400] around the Hα line from δ Scorpii It is superimposed with the atmospheric water vapor absorptions (H2O), displayed in red by the "lineident" database function For a commented spectrum refer to [33], Table 95A Analysis and Interpretation of Astronomical Spectra 115 26 Literature and Internet Literature: [1] Klaus Peter Schröder, – Feuriger Weltuntergang, Juli 2008, Sterne und Weltraum – Vom Roten Riesen zum Weissen Zwerg, Januar 2009 Interstellarum Sonderheft: Planetarische Nebel [2] Klaus Werner, Thomas Rauch, Die Wiedergeburt der Roten Riesen, Februar 2007, Sterne und Weltraum [3] James Kaler, Stars and their Spectra [4] Richard O Gray, Christopher Corbally, Stellar Spectral Classification, Princeton Series in Astrophysics [5] Keith Robinson, Spectroscopy, The Key to the stars [6] Stephen Tonkin, Practical Amateur Spectroscopy [7] Fritz Kurt Kneubühl, Repetitorium der Physik, Teubner Studienbücher Physik, Kap Relativistischer Doppler-Effekt der elektromagnetischen Wellen [8] J.-P Rozelot, C Neiner et al EDP Sciences: EAS Publication Series, Astronomical Spectrography for Amateurs, Volume 47, 2011 [10] G.A Gurzadyan, 1997,The Physics and Dynamics of Planetary Nebulae, [11] David F Gray, 2005, The Observation and Analysis of Stellar Photospheres, [12] A Unsöld, B Baschek, Der neue Kosmos [13] Erik Wischnewski, 2013, Astronomie in Theorie und Praxis, Auflage [14] Ken M Harrison, 2011, Astronomical Spectroscopy for Amateurs Articles by the Author and Reviews to the Spectroscopic Atlas: [20] Richard Walker, Die Fingerabdrücke der Sterne – Ein Spektralatlas für Amateurastronomen, June/July 2012, Interstellarum No 82 [21] Urs Flückiger, Kostenfreier Spektralatlas, April 2011, Sterne und Weltraum [22] Thomas Eversberg, Spektralatlas für Astroamateure von Richard Walker, VDS Journal für Astronomie, III/2011 [23] Richard Walker, Das Spektrum des Quasars 3C273, Orion 5/13 Internet Links: Author: The following publications on the topic can be downloaded at this link: http://www.ursusmajor.ch/astrospektroskopie/richard-walkers-page/index.html [30] Practical Aspects of Astro-Spectroscopy – Instructions and Information for Amateur Astronomers [31] Kalibrierung von Spektren mit der Xenon Stroboskoplampe (German language only) [32] Atomic Emission Spectroscopy with Spark- or Arc Excitation, Experiments with the DADOS Spectrograph and Simple Makeshift Tools [33] Spectroscopic Atlas for Amateur Astronomers (Download in German and English) [34] Kalibrierung von Spektren mit dem Glimmstarter ST 111 von OSRAM (German language only) [35] Quasar 3C273, Optical Spectrum and Determination of the Redshift Analysis and Interpretation of Astronomical Spectra 116 [36] Glow Starter RELCO SC480 – Atlas of Emission Lines – Recorded by the Spectrographs SQUES Echelle and DADOS Lectures/Practica: [50] Vorlesung Astrophysik, Max Planck Institut München: www.mpa-garching.mpg.de/lectures/TASTRO [51] Vorlesung Astrophysik, Astrophysikalisches Institut Potsdam http://www.aip.de/People/MSteinmetz/classes/WiSe05/PPT/ [52] F Royer: Rotation des étoiles de type A, Lecture Ecole d’Astronomie de CNRS http://adsabs.harvard.edu/abs/1996udh conf 159R [53] Gene Smith, University of California, San Diego, Astronomy Tutorial, Stellar Spectra http://cass.ucsd.edu/public/tutorial/Stars.html [54] Kiepenheuerinstitut für Sonnenphysik, Uni Freiburg: Grobe Klassifikation von Sternspektren http://www.kis.uni-freiburg.de/fileadmin/user_upload/kis/lehre/praktika/sternspektren.pdf [55] Michael Richmond: Luminosity Class and HR Diagram http://spiff.rit.edu/classes/phys440/lectures/lumclass/lumclass.html [56] Alexander Fromm, Martin Hörner, Astrophysikalisches Praktikum, Uni Freiburg i.B http://www.physik.uni-freiburg.de/~fromm/uni/Protokollschauinsland.pdf [57] University Heidelberg, Vorlesung Kapitel 3: Kosmische und Solare Elementhäufigkeit http://www.ita.uni-heidelberg.de/~gail/plvorl/Vorlesung-4.pdf [57a ] University Heidelberg, Anhang A: Elementhäufigkeiten http://www.ita.uni-heidelberg.de/~gail/astrochem/appA.pdf [58] Uni Karlsruhe: Spektroskopische Entfernungsbestimmung von Sternen oder Sternhaufen http://www.lehrer.uni-karlsruhe.de/~za3832/Astronomie/Spektroskopische%20Entfernungsbestimmung.pdf Spektroscopic atlases and commented spectra: [80] An atlas of stellar spectra, with an outline of spectral classification, Morgan, Keenan, Kellman (1943): http://nedwww.ipac.caltech.edu/level5/ASS_Atlas/frames.html [81]Digital Spectral Classification Atlas, R.O Gray: http://nedwww.ipac.caltech.edu/level5/Gray/frames.html [82] Moderate-resolution spectral standards from lambda 5600 to lambda 9000, Allen, L E & Strom, K M: http://adsabs.harvard.edu/full/1995AJ 109.1379A [83] An atlas of low-resolution near-infrared spectra of normal stars Torres Dodgen, Ana V., Bruce Weaver: http://adsabs.harvard.edu/abs/1993PASP 105 693T [84] Christian Buil: Vega Spectrum Atlas, a fully commented spectrum http://astrosurf.com/buil/us/vatlas/vatlas.htm [85] Paolo Valisa, Osservatorio Astronomico Schiaparelli, Varese http://www.astrogeo.va.it/astronom/spettri/spettrien.htm [86] High resolution solar spectrum Bass2000 http://bass2000.obspm.fr/download/solar_spect.pdf [87] NSO Digital Library NSO, Solar Spectral Atlases ftp://vso.nso.edu/pub/atlas/visatl/ [88] Caltech: Spectral atlases (also) for extragalaktic Objects http://nedwww.ipac.caltech.edu/level5/catalogs.html [89] UCM: Librerias de espectros estelares http://www.ucm.es/info/Astrof/invest/actividad/spectra.html Analysis and Interpretation of Astronomical Spectra 117 [90] various spectra of lamps: http://ioannis.virtualcomposer2000.com/spectroscope/index.html Databases [100] CDS Strassbourg: SIMBAD Astonomical Database http://simbad.u-strasbg.fr/simbad/ [101] NASA Extragalactic Database (NED) http://nedwww.ipac.caltech.edu/ [102] The SAO/NASA Astrophysics Data System, http://adsabs.harvard.edu/index.html [103] NIST Atomic Spectra Database: http://physics.nist.gov/PhysRefData/ASD/lines_form.html [104] MILES Spectral Library, containing ~1000 spectra of reference stars http://miles.iac.es/pages/stellar-libraries/miles-library.php [105] Flux Calibration Issues, A J Pickles, Caltech, 2007 http://adsabs.harvard.edu/abs/2007IAUS 241 82P [106] A Stellar Spectral Flux Library, 1150-25000 Å A J Pickles http://adsabs.harvard.edu/abs/1998PASP 110 863P http://www.stsci.edu/hst/HST_overview/documents/synphot/AppA_Catalogs5.html [107] A Library of Stellar Spectra, G.H Jacobi et al http://cdsarc.u-strasbg.fr/viz-bin/Cat?III/92 Publications to the Stellar Rotation Velocity: [120] Y Takeda et al.: Rotational feature of Vega and its impact on abundance determinations, 2007 Observat of Japan http://www.ta3.sk/caosp/Eedition/FullTexts/vol38no2/pp157-162.pdf [121] Nicholas A Moskovitz et al.: Characterizing the rotational evolution of low mass stars: Implications for the Li-rich K-giants, University of Hawaii at Manoa, http://eo.nso.edu/ires/IRES08/Nick_tech.pdf [122] F Fekel: Rotational Velocities of B, A, and Early‐F Narrow‐lined Stars (2003) NASA Astrophysics Data System or http://www.jstor.org/stable/10.1086/376393 [123] F Fekel: Rotational Velocities of Late Type Stars (1997) NASA Astrophysics Data System or http://articles.adsabs.harvard.edu/full/1997PASP 109 514F [124] F Royer: Determination of v sin i with Fourier transform techniques (2005) http://sait.oat.ts.astro.it/MSAIS/8/PDF/124.pdf [125] J.L Tassoul: Stellar Rotation, 2000, Cambridge Astrophysics Series 36, book preview: http://books.google.ch/books?q=tassoul [126] R.L Kurucz et al.: The Rotational Velocity and Barium Abundance of Sirius, The Astronomical Journal, Nov 1977 http://adsabs.harvard.edu/full/1977ApJ 217 771K [127] Reinhard W Hanuschik: Stellar V sin i and Optical Emission Line Widths in Be Stars, 1989 Astronomisches Institut Universität Bochum http://articles.adsabs.harvard.edu/full/1989Ap%26SS.161 61H [128] Christian Buil: Characterization of the Line Profile http://www.astrosurf.com/~buil/us/spe2/hresol7.htm Publications and Presentations to Be Stars [140] A Miroshnichenko: Spectra of the Brightest Be stars and Objects Description, University of North Carolina, www.astrospectroscopy.de/Heidelbergtagung/Miroshnichenko2.ppt [141] A Miroshnichenko: Summary of Experiences from Observations of the Be-binary δ Sco, University of North Carolina, www.astrospectroscopy.de/Heidelbergtagung/Miroshnichenko1.ppt [142] A Miroshnichenko et al.: Properties of the δ Scorpii Circumstellar Disk from Continuum Modeling, University of North Carolina, http://libres.uncg.edu/ir/uncg/f/A_Miroshnichenko_Properties_2006.pdf Analysis and Interpretation of Astronomical Spectra 118 [143] Reinhard W Hanuschik: High resolution emissionline spectroscopy of Be Stars, I Evidence for a two-component structure of the Hα emitting enveloppe, Astronomisches Institut Universität Bochum http://articles.adsabs.harvard.edu/full/1986A%26A 166 185H [144] S Stefl et al :V/R Variations of Binary Be Stars , ESO 2007 http://www.arc.hokkai-s-u.ac.jp/~okazaki/Meetings/sapporo/361-0274.pdf [145] R Soria: The Optical Counterpart of the X-ray Transient RX J0117.6-7330, Siding Spring Observatory Coonabarabran, Australia http://articles.adsabs.harvard.edu/full/1999PASA 16 147S [146] E Pollmann: Spektroskopische Beobachtungen der Hα- und der HeI 6678-Emission am Doppelsternsystem δ Scorpii, http://www.bav-astro.de/rb/rb2009-3/151.pdf [147] D K Ojha & S C Joshi: On the Shell Star Pleione (BU Tauri), 1991, Uttar Pradesh State Observatory, Manora Peak, http://www.ias.ac.in/jarch/jaa/12/213-223.pdf Publications to Novae [160] Donn Starkey, Photometry, Spectroscopy, and Classification of Nova V475 Scuti, JAAVSO Volume 34, 2005 http://articles.adsabs.harvard.edu/full/2005JAVSO 34 36S Publications/Practica to Spectroscopic Binaries [170] Juergen Weiprecht, Beobachtungsmethoden und Klassifikation von Doppelsternen, 2002, Praktikum Uni Jena http://www.astro.uni-jena.de/Teaching/Praktikum/pra2002/node155.html und http://www.astro.uni-jena.de/Teaching/Praktikum/pra2002/node156.html [171] Praktikum Uni Nürnberg-Erlangen, Die Masse eines Neutronensterns, http://pulsar.sternwarte.uni-erlangen.de/wilms/teach/intro/haus7_solution.pdf [172] Leifi, Uni München, Spektroskopische Doppelsterne, visuelle Doppelsterne: http://leifi.physik.uni-muenchen.de/web_ph12/materialseiten/m12_astronomie.htm [173] Southwest Research Institute Boulder, Eclipsing Binary Star Parameters, http://binaries.boulder.swri.edu/atlas/ [174] Diablo Valley College, Analyzing Binary Star Data, http://voyager.dvc.edu/faculty/kcastle/Analyzing%20Binary%20Star%20Dat4.htm#Introduction [175] Kiepenheuer Institut für Sonnenphysik: Einführung in die Astronomie und Astrophysik Kap 2.4 Zustandsdiagramme, http://www3.kis.uni-freiburg.de/~ovdluhe/Vorlesungen/E2_2/einf_2_Pt2.html [176] Dept Physics & Astronomy University of Tennessee, Spectroscopic Binaries http://csep10.phys.utk.edu/astr162/lect/binaries/spectroscopic.html [177] D.M Peterson et al The Spectroscopic Orbit of β scorpii A, 1979, Astronomical Society of the Pacific, http://adsabs.harvard.edu/abs/1979PASP 91 87P [178] Uni Freiburg: Einführung in die Astronomie und Astrophysik, 2.5 Zustandsdiagramme http://www3.kis.uni-freiburg.de/~ovdluhe/Lehre/Einfuehrung/Einf_2_3-5.pdf [179] Uni Heidelberg: Vorlesung Lektion 8: Doppelsterne und Binäre Pulsare, http://www.lsw.uni-heidelberg.de/users/mcamenzi/API_Lect8.pdf [180] Vorlesung TLS Tautenburg: Einiges über junge Sterne, http://www.tls-tautenburg.de/research/eike/vorles/entstehung_sterneEG04.pdf [181] Vorlesung University of Pennsylvania: Introduction to Least Squares Fit (with Excel) http://dept.physics.upenn.edu/~uglabs/Least-squares-fitting-with-Excel.pdf [182] Wikiversity: Least squares/Calculation using Excel: http://en.wikiversity.org/wiki/Least_squares/Calculation_using_Excel Analysis and Interpretation of Astronomical Spectra 119 Publications to Temperature of Stellar Photospheres [190] Measuring Starspot Temperature from Line Depth Ratios, Part I, S Catalano et al http://www.aanda.org/index.php?option=com_article&access=standard&Itemid=129&url=/articles/aa/abs/20 02/42/aa2543/aa2543.html [190b] Measuring Starspot Temperature from Line Depth Ratios, Part II, http://www.aanda.org/index.php?option=com_article&access=standard&Itemid=129&url=/articles/aa/ref/200 5/11/aa1373/aa1373.html [191] Effective Temperature vs Line-Depth Ratio for ELODIE Spectra, Gravity and Rotational Velocity Effects, K Biazzo et al http://web.ct.astro.it/preprints/preprint/biazzo2.pdf Publications to the Balmer-Decrement and IS Extinction [200] Calculations of level populations for the low levels of hydrogenic ions in gaseous nebulae, 1971, M Brocklehurst, http://adsabs.harvard.edu/full/1971MNRAS.153 471B [201] 3D Spektrophotometrie Extragalaktischer Emissionslinien Objekte, AIP 2001, Dissertation Jürgen Schmoll http://www.aip.de/groups/publications/schmoll.pdf [202] The Balmer Decrement in some Be Stars, 1953, G and M Burbidge http://articles.adsabs.harvard.edu/full/1953ApJ 118 252B [203] Paschen and Balmer Series in Spectra of Chi Ophiuchi and P Cygni, 1955 G and M Burbidge http://articles.adsabs.harvard.edu/full/1955ApJ 122 89B [204] Effects of Self-Absorption and Internal Dust on Hydrogene Line Intensities in Gaseous Nebulae, 1969, P Cox, W Mathews http://adsabs.harvard.edu/full/1969ApJ 155 859C [205] Comparison of Two Methods for Determining the Interstellar Extinction of Planetary Nebulae, 1992, G Stasinska et al http://articles.adsabs.harvard.edu/full/1992A%26A 266 486S [206] The Effect of Space Reddening on The Balmer Decrement in Planetary Naebulae, 1936, Louis Berman, http://adsabs.harvard.edu/full/1936MNRAS 96 890B [207] The Extinction Law in The Orion Nebula, R Costero, M Peimbert [208] A multiwavelength study of the Seyfert galaxy MCG-6-30, C S Reynolds et al http://adsabs.harvard.edu/abs/1997MNRAS.291 403R [209] A three-dimensional Galactic extinction model, F Arenou, M Grenon, A Gomez http://articles.adsabs.harvard.edu/full/1992A%26A 258 104A [210] The Balmer decrement of SDSS galaxies, Brent Groves, Jarle Brinchmann, Carl Jakob Walcher http://arxiv.org/abs/1109.2597 Publications/Practica to Emission Nebula [220] Emission Lines Identified in Planetary Nebulae, Y.P Varshni, et al., 2006 Univ Ottawa http://laserstars.org/ http://laserstars.org/data/nebula/identification.html [221] Gallery of Planetary Nebula Spectra, Williams College http://www.williams.edu/astronomy/research/PN/nebulae/ http://www.williams.edu/astronomy/research/PN/nebulae/legend.php [222] Planetarische Nebel, Frank Gieseking, 6-teilige Artikelserie, SUW 1983 [223] Balmer Line Ratios in Planetary Nebulae, Osterbrock et al., Univ Wisconsin 1963 http://adsabs.harvard.edu/full/1963ApJ 138 62O [224] Complex ionized structure in the theta-2 Orionis region, J R Walsh, Univ Manchester, 1981 http://articles.adsabs.harvard.edu/full/1982MNRAS.201 561W [225] An Evaluation of the Excitation Parameter for the Central Stars of Planetary Nebulae, W A Reid et al, Univ Sydney 2010 http://arxiv.org/PS_cache/arxiv/pdf/0911/0911.3689v2.pdf Analysis and Interpretation of Astronomical Spectra 120 [226] Excitation Class of Nebulae – an Evolution Criterion? G A Gurzadyan, A.G Egikyan, Byurakan Astrophysical Observatory 1990 http://articles.adsabs.harvard.edu/full/1991Ap%26SS.181 73G [227] The Planetary Nebulae, J Kaler, http://stars.astro.illinois.edu/sow/pn.html [228] A High-Resolution Catalogue of Cometary Emission Lines, M.E Brown et al http://www.gps.caltech.edu/~mbrown/comet/echelle.html [229] Optical Spectra of Supernova Remnants, Danziger, Dennefeld, Santiago de Chile 1975, http://articles.adsabs.harvard.edu/full/1976PASP 88 44D [230] Optical and Radio Studies of SNR in the Local Group Galaxy M33, Danziger et al 1980, ESO http://www.eso.org/sci/publications/messenger/archive/no.21-sep80/messenger-no21-7-11.pdf [231] Emission-line spectra of condensations in the Crab Nebula, Davidson 1979 http://adsabs.harvard.edu/abs/1979ApJ 228 179D [237] Übungen zur Vorlesung Stellare Astronomie und Astrophysik, Konstruktion eines einfachen Modellprogramms für einen Gasnebel, H.P Gail, W.M Tscharnuter, Univ Heidelberg, http://www.ita.uni-heidelberg.de/~gail/aastern/uebSS06-hii.pdf [238] Astronomisches Praktikum, Versuchsanleitungen, Spektroskopische Diagnostik einer Emissionsliniengalaxie, Univ, Hamburg http://www.hs.uni-hamburg.de/usr/local/hssoft/prakt/doku/Anleitungen/Praktikum.pdf [239] Astrophysics graduate course 25530-01 Lecture and 7, Uni Basel http://phys-merger.physik.unibas.ch/~cherchneff/Site_2/Teaching_at_UniBasel.html Publications to White Dwarfs [250] A Gravitational Redshift Determination of the Mean Mass of White Dwarfs DA Stars, Ross E Falcon et al 2009, http://arxiv.org/pdf/1002.2009v1.pdf Publications to Calibration and Normalisation of Spectral Profiles [300] A Method of Correcting Near-Infrared Spectra for Telluric Absorption, William D Vacca et al http://arxiv.org/abs/astro-ph/0211255 [301] Common Methods of Stellar Spectral Analysis and their Support in VO, Petr Skoda http://arxiv.org/abs/1112.2787 [302] SISD Training Lectures in Spectroscopy - Anatomy of a Spectrum, Jeff Valenti, STSCI www.stsci.edu http://www.stsci.edu/hst/training/events/Spectroscopy/Spec02Nov09.pdf [303] SN Factory Spectrophotometry Requirements Document, Greg Aldering http://snfactory.lbl.gov/snf/ps/flux_calib.ps [304] ESO RA Ordered List of Spectrophotometric Standards http://www.eso.org/sci/observing/tools/standards/spectra/stanlis.html [305] Precision Determination of Atmospheric Extinction at Optical and Near Infrared Wavelengths, David L Burke et al http://iopscience.iop.org/0004-637X/720/1/811 [312] Absolute Flux Calibrated Spectrum of Vega, L Colina, R Bohlin, F Castelli www.stsci.edu [313] Measurement of Echelle Spectrometer Spectral Response in UV, J Rakovský et al www.mff.cuni.cz [314] Towards More Precise Survey Photometry for PanSTARRS and LSST: Measuring Directly the Optical Transmission Spectrum of the Atmosphere, W Stubbs et al http://arxiv.org/pdf/0708.1364.pdf [315] Addressing the Photometric Calibration Challenge: Explicit Determination of the Instrumental Response and Atmospheric Response Functions, and Tying it All Together, W Stubbs, J L Tonry http://arxiv.org/abs/1206.6695 Analysis and Interpretation of Astronomical Spectra 121 [316] Toward 1% Photometry: End-to-end Calibration of Astronomical Telescopes and Detectors, W Stubbs, J L Tonry http://arxiv.org/pdf/astro-ph/0604285v1.pdf Spectrographs and Cameras: [400] SQUES Echelle Spektrograf, Eagleowloptics Switzerland [401] DADOS Spektrograph, Baader Planetarium: http://www.baader-planetarium.de/dados/download/dados_manual_english.pdf [402] Shelyak Instruments: http://www.shelyak.com/ [403] SBIG Spectrograph DSS-7 http://ftp.sbig.com/dss7/dss7.htm Spectroscopic Software: [410] IRIS and ISIS, Webpage of Christian Buil http://www.astrosurf.com/buil/ [411] Vspec: Webpage of Valerie Désnoux http://astrosurf.com/vdesnoux/ [412] RSpec: Webpage of Tom Field http://www.rspec-astro.com/ [413] SpectroTools: Freeware program by Peter Schlatter for the extraction of the H2O Lines http://www.peterschlatter.ch/SpectroTools/ [414] MIDAS, ESO http://www.eso.org/sci/software/esomidas/ [415] IRAF, NOAO, http://iraf.noao.edu Miscellaneous [420] Intrinsic Colors of Stars in the Near Inrared, Jorge R Ducati et al 2001, http://iopscience.iop.org/0004-637X/558/1/309/fulltext/ [421] The Intrinsic Colours of Stars and Two-Colour Reddening Lines, M Fitzgerald, 1970 http://articles.adsabs.harvard.edu/full/1970A%26A 234F General Astro-Info, Forums and Homepages: [430] Verein Astroinfo, Service für astronomische Informationen www.astronomie.info [431] Lexikon Astronomie Wissen, Andreas Müller, TU München http://www.wissenschaft-online.de/astrowissen/ [440] SAG: http://www.astronomie.info/forum/spektroskopie.php [441] VdS: http://spektroskopie.fg-vds.de/ [480] Regulus Astronomy Education, John Blackwell http://regulusastro.com/blog/?page_id=2 [481] Robin Leadbeater's observatory http://www.threehillsobservatory.co.uk/ [482] Dr Erik Wischnewski, http://www.astronomie-buch.de/ ... Interpretation of Astronomical Spectra Photons – Messengers from the Universe 2.1 Photons – Carriers of Information Photons are generated in stars, carrying valuable information over immense periods... “destruction” takes place in a variety of physical processes Relevant for the spectroscopy are electron transitions between different atomic orbital (details see later) – A photon always moves with... accepted 7.5 , Equivalent Width The EW-value or Equivalent Width is always based on the continuum level relative measure for the area of a spectral line and is a Definition The -value must therefore