Univ. Belgrade
Prof. L.Č. Popović
Line Shape in Astrophysics
(S3, elective, 6 ECTS)
Learning Outcomes:Spectral lines are emitted from different celestial sources, from interstellar matter to the distant quasars. The line intensity and their shapes can be used as a tool to investigate the physical conditions in the regions, which are emitting the lines. The course is mostly organized as practical work with the observed lines from different celestial object. This provides that students will effectively learn to use the line shape and intensity to explore physical properties of line emitting sources (which can be from nebulae-stars to quasars). The main outcomes are: 1. Learn about different type of lines which can be observed in astrophysics (absorption vs. emission lines, lines from high ionized atomic states, etc.); 2. To use line shapes and intensities to determine physics and kinematics of emitting regions.; 3. Learn about specific spectral line shapes (line shapes from the accretion disc, P-Cyg profile, line-profile from inflow-outflow and rotation).
Knowledge and Understanding:
The course has two parts: 1. Lectures given on classical way with the aim to give the basic knowledge about the line forming mechanism in different objects; 2. Practical exercises (work on the observational spectroscopic data). The lecturing and practical exercising are well coordinated and scheduled, starting first from thematic lecture that is following by the corresponding exercise. After students finish the exercise, they should send written report to the professor, with description of the work, and obtained results, with a small discussion of obtained results. The experience of the past years has been quite positive, showing that this way of work with students gives good results in understanding the subject. The formal verification of the learning outcomes are carried out at the end of the course with an oral examination (and taking into account the reports from practical exercises).
Applying Knowledge and Understanding:This course gives a very useful practical and theoretical base for using the spectral lines for diagnostic of the physical properties in different celestial objects. This is very important in the work with spectral observational data, e.g. after the course, students should be able to immediately recognize the source of the line emission (nebulae, stars, quasars, etc.). Additionally, using some spectral analysis students should be able to find some physical properties of observed objects.
PrerequisitesBasics of Atomic Physics.
ProgramProgram of the course covers the following themes: 1. Transitions in atom-ions (free-free, bound-free, bound-bound) – line emission; 2. Line parameters: intensity, width and shift; different line profiles, Lorentzian, Gaussian and Voight line profiles – Exercise: Plot different line profiles and discuss the difference btw profiles, find connection between the profile line width and Full Width at Half Maximum); 3. Lorentz profile: Natural and Collisional Broadening (Stark, Van der Waals and Resonant broadening) – Exercise: Calculate natural broadening for H_alpha and H_beta line from Balmer series. 4. Gaussian profile: Kinematics of emitting gas – Exercise: From stellar spectra (stars different classes) find the parameters of Balmer lines. Fit the lines with Gaussian and Lorentzian profiles. 5. Influence of rotation and systemic motion on the line profiles – Exercise: Explore line profiles of P-Cyg profiles taken from star and quasar spectra; 6. Polarization in lines. Polarized line profiles (from stars to quasars). 7. A set of practical works (exercises) ‘Lines as tools for physical properties determination’; a) Determination the outflow velocities from P-Cyg profile; b) modeling the accretion disc line profile of Fe Kalpha observed in active galaxies; c) Determination supermassive black hole masses of active galaxies from H_beta line.
Description of how the course is conductedClassroom lectures, numerical and practical exercises
Description of the didactic methodsLectures are in the form of presentations, but also there are some small problems to solve during the lecture time and during numerical exercises. Exercises: students are asked to be prepared to search for data and for corresponding literature before starting with work on well defined problem.
Description of the evaluation methodsQuestions during the numerical exercises, and during lecture, also during presentations of the project, students are asked to demonstrate an understanding of the subject.
Adopted TextbooksNotes of lectures ‘Line shapes in astrophysics’
Recommended readingsSeveral specialized papers which are devoted to the special exercise The course is specific in the part that a student has to read given instructions (and papers) before doing an exercise.