Ast 622: The Interstellar Medium

Fall 2009 MWF 1-2pm

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, $\gt 10^6$ K, to the very cold, $\lt 10$ K. Observed densities span an even wider dynamic range, from $\lt 10^{-3}$ to $\gt 10^6$ particles per cubic centimeter. Even the highest densities, however, are far 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, molecular clouds. We will end with an overview of the circumstellar medium: protostellar cores and protoplanetary disks.

The class will closely follow a relatively new book, ``The Physics and Chemistry of the Interstellar Medium'' by Xander Tielens (Cambridge University Press). I will augment the material with additional notes and illustrative journal articles, linked below. After the first month, once you have built up a foundation of the underlying physical principiles, we will spend one lecture a week in a round-table journal club style.

Graduate education is not about book learning. As you carry out your PhD research you need to know, and know how to apply, physical concepts. In both collaborations and conferences, you will often need to discuss your data and analysis verbally. This is the main reason for the oral nature of the qualifying exam that you will take at the start of your third year. There will be a small number of written problem sets but you will mainly be graded on an oral midterm and final. You will also be required to lead one of the journal club sessions and discuss a recent paper that highlights some of the concepts we have learned at the end of the semester. This applies to those who are auditing the class - there is no free lunch! The breakdown of the grading is as follows: problem sets (30%), journal club (15%), midterm (20%), final (35%).

The lectures and handouts will be posted online here. Note that these are subject to change right up to the time of the lecture and that they these are mainly placeholders for discussion and elaboration on the board so are poor subtitutes for being in class.

Provisional class schedule Introduction Gas Cooling Characteristic energies of electronic, vibrational, and rotational transitions Gas Heating Chemical Processes Interstellar Dust Measuring the dust mass from long wavelength observations Polycyclic Aromatic Hydrocarbons HII regions How ionized are HII regions? The three level system The lifetime problem for UC HII regions The Phases of the ISM The two-phase atomic ISM The hot ionized medium Photodissociation Regions Molecular Clouds The CO-to-H$_2$ conversion factor Deriving column densities from line integrated intensities Dynamics Waves Shocks

DISCUSSION PAPERS 9/30/09 Super Star Clusters (Turner et al. 2000, 2003) Free-free emission / Infrared recombination lines 10/16/09 The Warm-Hot Ionized Medium (WHIM) PT News / Science Perspective 10/30/09 Chemistry in low-mass protostellar and protoplanetary regions (van Dishoeck 2006) online / PDF