Ast 622: The Interstellar Medium
Spring 2012 TuTh 2:30-4pm
Jonathan Williams, Institute for Astronomy

 

The Interstellar Medium (ISM) is the gas and dust between the stars. Stars form from it, their winds and supernova enrich and replenish it. Temperatures in the ISM range from the very hot, >10⁶K, to the very cold, <10K. Observed densities span an even wider dynamic range, from <10^-3 to >10⁶ particles per cubic centimeter. Even the highest densities, however, are more rarefied than the best vacuums currently attainable on Earth and thus the ISM allows us to explore physical processes in unique environments. This course will cover observations and theories of a wide range of ISM environments from pervasive diffuse, ionized gas to dense, star forming cores in molecular clouds.

Several new books have appeared on this topic in recent years and I will use material from

• "The Physics of the Interstellar and Intergalactic Medium'' by Bruce Draine -- the official course book
• "The Physics and Chemistry of the Interstellar Medium'' by Xander Tielens
• "Physics and Chemistry of the Interstellar Medium'' by Sun Kwok
• "The Interstellar Medium'' by James Lequeux

However, I will strive to keep this course in touch with current research rather than a dry recitation of old results. The goal is for you to see applications of the physics through both classic and recent papers. Therefore, I will assign reading material from the Draine book for background and derivations, my own handouts where necessary, and papers. My aim is that you have the material available to learn at your own pace so that we can use the class time to review the reading, discuss, and solve problems.

There will be short problems sets most weeks. The final exam will be oral, both because I think this is the best way to figure out how well a student understands the material and also to prepare you for the qualifying exam. Each student will write a short course paper on a specific ISM-related topic of their choosing and present it in a pecha-kucha format (20 slides, each 20 seconds long). The breakdown of the grading is as follows: problem sets (40%, one can be skipped without penalty), course paper and presentation (20%), and final (40%).

 

Class calendar

 

Syllabus

1. Some fundamentals
   • Statistical mechanics
   • The non-equilibrium ISM
   • Radiative transfer
   • Fluid dynamics
   
   
2. Dust
   • Reddening and extinction
   • Mie theory
   • Grain size and composition
   • Gas-to-dust ratio
   
   
3. Ionized regions
   • Stromgren sphere
   • Bremsstrahlung radiation
   • HeII regions
   • The 2-level system
   • The 3-level system
   
   
4. Atomic regions
   • The 21cm line
   • Equivalent width
   
   
5. Heating and cooling
   • Heating and cooling mechanisms
   • The 2-phase ISM
   • The 3-phase ISM
   
   
6. Molecules
   • Vibrational and rotational states
   • Masers
   • Molecular hydrogen
   • Carbon monoxide
   • Molecular clouds
   • Astrochemistry
   • Photon dominated regions
   
   
7. Dynamics
   • Expanding HII regions
   • Expanding supernova remnants
   • The Bonnor-Ebert sphere
   
   
8. The circumstellar medium
   • Disk formation
   • Disk evolution
   
   

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Ast622 The Interstellar Medium (Jonathan Williams, IfA)