uks001.jpgC1 Astrophysics : Trinity Term 2016. 


Atomic Processes and the Interstellar Medium


Patrick Roche


This part of the course describes how quantitative information on physical conditions in diffuse matter and element abundances is obtained through analysis of spectroscopic observations


The synopsis for the lectures is:

„Astronomical spectroscopy, lines in different spectral regions, atomic physics and selection rules, forbidden and allowed transitions

„The two level atom, A, B and C coefficients and their useful regimes, thermal populations,  IR fine structure lines, critical density, mass estimates

„Recombination and ionization processes, the Stromgren sphere, ionization balance,  effective temperature estimates.

„The 3 level atom: diagnostics of electron temperature  and electron density.

„Absorption lines, equivalent width and the curve of growth. Column densities and abundances

„The interstellar medium.  Atomic and ionic absorption lines, abundance of gas, molecules and dust.  Hyperfine transitions: 21cm line of H, Galactic structure

„Interstellar extinction, dust components, thermal emission, equilibrium and stochastic processes

„The sun.  Ionization and sources of opacity, radiative transfer, the Gray atmosphere, limb darkening, absorption line formation


There will be two classes covering this material, and handouts are available here


There are many text books that cover this material, but good recent sources are:

Physics & Chemistry of the Interstellar Medium,  by Sun Kwok  (University Science Books, Sausalito, California) ISBN-10: I-891389-46-7

Note that the second half of the book goes into much more detail than can be covered in the 8 lectures provided in C1.


Physics of the Interstellar and Intergalactic Medium, by Bruce Draine. (Princeton University Press) ISBN-10: 0691122148