67100 - Radiation Processes and Mhd

Learning outcomes

At the end of the lectures each student will possess a comprehensive knowledge of the astrophysical processes generating photons at various locations in the Universe (stars, star forming regions and interstellar medium, galaxies, intergalactic medium, hot plasma, etc.) in a range of physical conditions (temperature, density, pressure, etc.). In particular every student will be able to interpret the emitted spectrum of any celestial body, and then infer the processes responsible for the generation of the observed photons, and derive the main astrophysical quantities such as, density, temperature, magnetic field, energy content, pressure, etc.
Students will be also familiar with general concepts concerning astrophysical fluids and plasmas (with magnetic fields). *IT IS VERY IMPORTANT that the student already has passed the exam FISICA GENERALE II, for a fitful study of this course.

Course contents

Summary of principles of hydrostatics. Fundamentals of hydrodynamics: equations of conservation of mass, of Euler or Navier-Stokes, conservation of energy in a fluid. Sound waves; shock waves - Fundamentals of Magneto-Hydro-Dynamics (MHD): magnetic forces, fields frozen in the matter; Alfven waves. Origin of magnetic fields in astrophysics. Radiative transfer in astrophysics- Continuum emission processes. Black body and the Plank's function. Properties. Stars as Black Bodies. Color Index and the H-R Diagram. Thermal and relativistic bremsstrahlung, cyclotron and synchrotron radiation. Photon-electron scattering, Thomson, Compton and Inverse Compton. Sunyaev-Zeldovich effect. Wave propagation in a plasma: dispersion measure; Faraday rotation. Particle acceleration in astrophysics (Fermi mechanism): stochastic and systematic acceleration - Cosmic rays: general properties, composition and origin - The InterStellar Medium; the role of the dust. Statistical laws and thermodynamic equilibrium; detailed statistical equilibrium, Einstein's coefficients for radiations and collisions; population of energy levels in the ISM. Emission and absorbption in atoms and molecules (HI, CO, CN). Determination of the temperature and density from line spectra. =
A number of simple astrophysical problems will be discussed and solved, to prepare the students for the test of admission to the oral exam and to the partial tests as well.

Readings/Bibliography

 - M.S. Longair: "High energy Astrophysics" - Cambridge University Press (English)

 -  Rybicki & Lightman "Radiative processes in astrophysics"  - Wiley (English)

 - C. Clarke & Carswell "Principles of  Astrophysical Fluid Dynamics", Cambridge University Press (English)

During lectures the various sections of the aforementioned textbooks will be indicated as relevant for the optimum study. Additional textbooks will be mentioned as alternative reference.

Teaching methods

Lectures, in which it will be discussed how information on fundamental physics and gas thermodynamics are derived from simple astronomical measurements. A number of astrophysical examples will be discussed, in the light of the role of the basic astrophysical processes in producing the radiation observed. Some simple application (exercise) will show how to take advantage of the concepts faced during lectures. Physical parameters of astrophysical bodies will be derived starting from observational data.

 

Assessment methods

A 90-min written test composed by 3 questions (1 in an open form made of statements to comment on) allows the admission to the oral exam. During the written test it is possible to use lecture notes and books. The test possible outcomes are: admitted, partial admission, not admitted. The final grade will be defined after the oral exam. This latter is made of three main questions (~15' each) in which the candidate is supposed to describe the main subjects seen during the lectures.

Starting from AY 2022/23,  3 short tests (approx around 20.10, 20.11 and 15.12) are organised. If passed, the candidate is directly admitted to the oral exam.

Teaching tools

Slide projector (from a notebook - copy of the slides is available to students on the website); also a blackboard will be used, also for solving problems like the ones in the final test.

Links to further information

http://www.ira.inaf.it/~ddallaca/P-RAD.html

Office hours

See the website of Daniele Dallacasa