Interstellar Medium 2012 Q4

Lecturer: Floris van der Tak

Assistant: Yunhee Choi


The interstellar medium (ISM) is the place where material from old stars gets recycled into new generations of stars. The ISM thus plays a central role in the evolution of galaxies and of matter in the Universe. This course teaches the concepts necessary to understand the ISM: the physics of rarefied gases under various conditions. These concepts have applications in all branches of astrophysics.


After following the course, the student will be able to:

  1. describe the diagnostics of rarefied gases: explain what types of gas emit radiation at which wavelengths, and how the spectral lines of atoms and molecules may be used to determine the conditions of a gas;

  2. describe the heating and cooling of rarefied gases: tell the main mechanisms which influence the gas temperature and explain when which mechanisms play a role;

  3. describe the dynamics of interstellar gases: explain which processes cause motions in the gas, and when which process plays a role;

  4. describe the conditions for star formation: explain which conditions in the interstellar medium are necessary and sufficient for the formation of new stars.

These goals will be achieved at two levels: a theoretical level where the student can express insight, and a practical level where this insight is applied in calculations.

Book (required)

Physics of the Interstellar and Intergalactic Medium, Bruce T. Draine, Princeton Series in Astrophysics, ISBN 9780691122137 (hardcover) or 9780691122144 (paperback).


Astrophysics B / Radiative Processes in Astrophysics: the book by Rybicki & Lightman.

Students must register for the course at least two weeks before the first lecture, i.e., by week 15. The book by Draine may take a week or more to be delivered, so it also should be ordered by week 15. Registration should be done by e-mailing Floris van der Tak, with a cc to Gineke Alberts; see below for contact info. The homework for the first lecture is to read the first chapter from Draine's book.


The course consists of 2x2 hours of lectures and 1x2 hours of practical work per week, over a period of 8 weeks. Before each lecture, the students read the relevant chapter of the book. In the lectures, the course material is introduced and illustrated with examples. At the end of each lecture, the homework assignments for the following practical work session are handed out. The students prepare answers to each question in the form of a short (~1 page per subquestion) digital slide show (using PowerPoint, Keynote, OpenOffice, or a similar program) and send a PDF version by e-mail to the assistant by Thursday 12:00 noon. In the practical sessions, a randomly selected student presents his/her solution to the question, and the group discusses this solution. The quality of these presentations and participation in these discussions together form 1/4 of the grade for the course.


After the last week of lectures, there is a written exam in two parts. The first part consists of questions into knowledge and insight of the course material, which must be answered without the book. The second part consists of application-type questions which may be answered using the book. The final grade for the course is a weighted average of the grades for the exam (75%) and for the homework assignments (25%).


The basic schedule is given on the Ocasys page but see the table below for exceptions. The chapters in column 3 are the homework for that lecture. You can skip the sections marked by (*) in the book.



Book chapter


I. Overview of the ISM

1, 12, 40

Part 1: Regions of ionized gas


II. Pure hydrogen nebulae

3, 4, 10, 11


Problem Set 1


III. Nebulae with heavier elements

6, 14 (incl. 14.3), 15 (incl. 15.8)


IV. Heating & cooling of H+ regions

2, 27


V. Diagnostics of H+ regions

17, 18, 28


VI. Non-stellar H+ regions

13, 16, 20 (incl. 20.2 & 20.3)


Problem Set 2

Part 2: Regions of neutral gas


VII. Observational probes of neutral gas

8, 9, 29


Problem Set 3

11:00-13:00, room 257


Problem Set 4

11:00-13:00, room 257


VIII. Thermal balance of neutral gas



IX. Interstellar shock waves

35, 36 (incl. 36.6)


Problem Set 5


X. The multi-phase ISM

34, 39

Part 3: Regions of molecular gas


XI. Molecular spectra

5, 7, 19, 31


Problem Set 6


XII. Interstellar dust

21, 22, 23, 24, 25

06-06-2012 (257)

XIII. Diffuse molecular clouds & PDRs

32, 33


Problem Set 7


XIV. Dense molecular clouds & star formation

41, 42


XV. The extragalactic ISM


Problem Set 8


Exam = deadline assignments

09:30-12:00; room 161


Floris van der Tak:

telephone (050) 363 8753

e-mail f.f.s.van.der.tak AT

office: 5419.0294 (Kapteynborg, second floor)

Yunhee Choi:

telephone (050) 363 4276

e-mail y.choi AT

office 5419.0254 (Kapteynborg, second floor)

Gineke Alberts (Education Secretary):

telephone (050) 363 4073

e-mail m.g.alberts AT

office 5419.0178 (Kapteynborg, first floor)