Ay 121: Radiative Processes

Instructor: S. R. Kulkarni, 1030-1200 (Tuesday & Thursday)

In this course, I will follow closely the classic textbook "Radiative Processes in Astrophysics" by Rybicki & Lightman. Many observers focus on Data analysis (informatics). This is a powerful tool but is not the basis of the field. In my view, success in astronomy rests upon having a sound foundation in physics and mathematics. As an observer I find myself to refresh undergraduate physics now and then. The classic book on E&M by Purcell has now been vastly revised (Purcell & Morin). I am frequently reaching to it to brush up on undergrad physics.
High Energy Astrophysic by M. Longair (volume 2). Available electronically  | 

Grading: Please remember that the goals in graduate school are different from those in colleges. Here, you aim for understanding, period. Homeworks will be posted every Friday and due midnight the next Friday. A good teacher can catalyze understanding and an excellent teacher can provide unique insights. I have observed that much of learning is peer-to-peer (which is why it is profitable to attend selective colleges). Bearing these observations in mind try to first work out the homework on your own. If you meet a dead end then discuss with a classmate(s). However, what you turn in must be your own work. You can skip one home work during the term.
The final exam will be an oral exam with questions given to the class 2 weeks in advance. You will be asked five questions (at random) from this set. The exam will last up to an 1 hour. Homeworks will be given 3/4 weight with the remaining 1/4 for the final exam. During mid-terms (the week is TBD) we will have a short (30 minute) oral exam in lieu of a homework. It is meant to make students familiar with the framework of oral exams.

My goal is to follow the book closely. However, I will be adding some additional material (and note as SRK notes). In some cases, I will provide the notes by the way of a link to a pdf file.

There are really some very good courses on YouTube now. I will use this spot to list interesting courses.
There is a separate class on fluids. We will be making use of some aspects of fluid mechanics. I found the Introductory talks on Fluid Mechanics by Professor Cimbala, PSU, to be very helpful.

  1. October 1
    Introductory talk stressed the importance of remembering basic constants, the value of "pre-computing", and the benefits of making order of magnitude estimates. Flux density, Photo-electric effect is at the base of detection, Mandel's semi-classical formulation, wave-noise and photon noise (SRK). Jansky and Rayleigh units. Motivating Intensity.

  2. October 3
    Preparatory work: Please review semi-classical derivation of Planck's formula; phase space in quantum mechanics. Bose-Einstein statistics
    Formal definition of intensity. Moments of intensity (energy density, flux density, pressure) (Chapter 1.3). Planck's (semi-classical) derivation of blackbody intensity. Photons follow Bose-Einstein statistics (Chapter 1.5). QM derivation of Planck formula. Photon occupation index (cf. Chapter 4.9). Invariance of I_nu/nu^3 and some consequences (SRK)
    "Why nu f_nu?"  |  Homework 1

  3. October 8
    Preparatory work: Please review Einstein A and B coefficients
    Absorption coefficient, emissivity, basic radiative transfer equation, source function, mean free path (Chapter 1). Kirchoff's law. (Chapter 1). Two-level atom in radiation field: Einstein A and B coefficients. Generalized Kirchoff's law (Chapter 1.6). Two-level atom with collisional excitation and collisional de-excitation. Introduction to permitted (large A_21), semi-forbidden and forbidden (very small A_21) lines.
    SRK Notes (cf. Sections 17.1, 17.2 of Draine's ISM book).

  4. October 10
    Poynting Vector (Chapter 2.1) and Electro-magnetic waves in vacuum (Chapter 2.2). Fourier Transfor (SRK). Introducing the power spectrum (Chapter 2.3).
    Vector Algebra & Vector Calculus Identities  |  Homework 2

  5. October 15
    Preparatory work: Please reread your old textbooks and become familiar with vector potential for magnetic field. Review Poisson's equation and Green's function.
    Radiation from moving charges. Electromagnetic potentials (Chapter 2.5). Linenard-Wiechart potential (Chapter 3.1). Velocity & Acceleration fields (Chatper 3.2).
    Gauge selection  |  Poisson's Equation  |  History of Gauge Choices.

  6. October 17
    Larmor Formula & Dipole approximation (Chapter 3.3) Thompson scattering (Chapter 3.4)
    Homework 3

  7. October 22
    Basic Fluid Mechanics.
    Material Derivative (Cimbala)  |  Fluid Mechics-Intro

  8. October 24
    Maxwell-Boltzman equations. EM waves in plasma, dispersion relation and group velocity (Chapter 8.1). Polarization and Stokes parameters (Chapter 2.4)
    SI constants  |  Waves in Plasma  |  Secret handshakes

    Master List of Questions for the Midterm Exam. (Exams: October 24, 25).

  9. October 29
    Polarization due to Thompson scattering (3.4)
    Thermal (non-relativistic) Bremsstrahlung (5.1)

  10. October 31
    Thermal bremsstrahlung (5.2, 5.3).
    Radio & FIR sky

  11. November 5
    Preparatory work: Please review QM of hydrogen & helium
    Atomic Spectroscopy: Hydrogen. Alkalis. Helium. (Chapter 9)
    Relativistic Effects  |  Alkali Spectra  |  Helium
    Homework 4

  12. November 7
    Multi-electron atoms (Aufbau). LS and JJ coupling (Chapter 9).
    Aufbau Principle  |  LS & JJ Coupling
    Useful material: Unix Term Program  |  Definitive guide for labeling levels  |  Examples of Ground terms

  13. November 12 (Phinney)
    Preparatory work: Read up on basics of special relativity (time dilation, length contraction, Doppler effect, addition of velocity, aberration); see, for instance, Chapter 4.1.
    First introduction to electric and magnetic fields in moving frames (4.5). Fields of uniformly moving charge (4.6).

  14. November 14 (Phinney)
    Advanced Special Relativity (Chapter 4.7 and 4.8).

  15. November 19
    Cosmic Synchrotron Emission Presentation; Synchroton (Chapter 6.1,6.2); beaming fraction.

  16. November 21
    Synchrotron (6.3, skimming 6.4, 6.5, 6.6,i 6.7, skimming 6.8)

  17. November 26
    Compton Scattering (Chapter 7)

  18. December 3
    Interaction of radiation with atoms (Chapter 10)

  19. December 5
    Molecular Spetroscopy (Chapter 11)