Ay 121: Radiative Processes
Instructor: S. R. Kulkarni, 10301200 (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 peertopeer (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 midterms (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.
 October 1
Introductory talk stressed the importance of remembering basic
constants, the value of "precomputing", and the benefits of making
order of magnitude estimates. Flux density, Photoelectric effect
is at the base of detection, Mandel's semiclassical formulation,
wavenoise and photon noise (SRK). Jansky and Rayleigh units.
Motivating Intensity.
 October 3
Preparatory work: Please review semiclassical derivation of Planck's
formula; phase space in quantum mechanics. BoseEinstein
statistics
Formal definition of intensity. Moments of intensity (energy density, flux
density, pressure) (Chapter 1.3). Planck's (semiclassical) derivation of
blackbody intensity. Photons follow BoseEinstein 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
 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). Twolevel atom in radiation field:
Einstein A and B coefficients. Generalized Kirchoff's
law (Chapter 1.6). Twolevel atom with collisional excitation and
collisional deexcitation.
Introduction to
permitted (large A_21), semiforbidden and forbidden (very small A_21) lines.
SRK Notes (cf. Sections 17.1, 17.2
of Draine's ISM book).
 October 10
Poynting Vector (Chapter 2.1) and Electromagnetic waves in vacuum
(Chapter 2.2). Fourier Transfor (SRK). Introducing the power spectrum
(Chapter 2.3).
Vector Algebra & Vector
Calculus Identities 
Homework 2
 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).
LinenardWiechart potential (Chapter 3.1). Velocity & Acceleration
fields (Chatper 3.2).
Gauge selection
 Poisson's Equation
 History of Gauge
Choices.
 October 17
Larmor Formula & Dipole approximation (Chapter 3.3)
Thompson scattering (Chapter 3.4)
Homework 3
 October 22
Basic Fluid Mechanics.
Material Derivative (Cimbala)
 Fluid MechicsIntro
 October 24
MaxwellBoltzman 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).
 October 29
Polarization due to Thompson scattering (3.4)
Thermal (nonrelativistic) Bremsstrahlung (5.1)
 October 31
Thermal bremsstrahlung (5.2, 5.3).
Radio & FIR sky
 November 5
Preparatory work: Please review QM of hydrogen & helium
Atomic Spectroscopy:
Hydrogen. Alkalis. Helium.
(Chapter 9)
Spinorbit coupling
 Alkali Spectra
 Helium
Homework 4
 November 7
Multielectron atoms (Aufbau). LS and JJ coupling.
Aufbau Principle 
LS, JJ Coupling
Useful material:
Unix Term Program

Definitive guide for
labeling levels

Examples of Ground terms
 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).
 November 14 (Phinney)
Advanced Special Relativity (Chapter 4.7 and 4.8).
 November 19
Synchroton (Chapter 6)
 November 21
Synchrotron; Compton Scattering (Chapter 7)
 November 26
Compton Scattering (Chapter 7)
 December 3
Interaction of radiation with atoms (Chapter 10)
 December 5
Molecular Spetroscopy (Chapter 11)