Description
Covers gas and dust in galaxies, atomic and molecular clouds, emission and absorption lines, H II regions, star formation, shocks, cosmic rays, magnetic fields, and multiwavelength ISM diagnostics (the official catalog description). Every physical tool developed in this course — the 21 cm hyperfine radiative-transfer solution and HI column-density formula, the Cardelli extinction-curve parametrization, the CO-to-H2 mass conversion and the virial theorem, the Jeans instability criterion and free-fall collapse time, the Stromgren-sphere ionization-balance derivation and nebular emission-line diagnostics, the Rankine-Hugoniot shock-jump conditions, and the cosmic-ray power-law spectrum — is derived from first principles and then applied to real, standard published interstellar-medium data: the 3C 273 and Cygnus X-1 HI/X-ray sightlines, the heavily reddened star Cygnus OB2 No. 12 and the anomalous-extinction sightline HD 200775, the real Orion and Taurus Molecular Clouds, the classic Bok globule Barnard 68, the Orion and Rosette Nebulae, the Cassiopeia A and Tycho supernova remnants, and the Crab Nebula; see reference-log.md for full data provenance.
Learning Outcomes
- Derive the ideal-gas pressure-balance condition among the interstellar medium's phases and the thermal-instability criterion that sorts the neutral ISM into discrete stable phases.
- Derive the 21 cm hyperfine radiative-transfer solution and the resulting HI column-density formula, and apply both to real published HI sightline data.
- Derive the relationships among optical depth, extinction, color excess, and R_V, and apply the Cardelli, Clayton & Mathis (1989) extinction-curve parametrization to real reddened stars.
- Derive the CO-to-H2 mass conversion and the virial-mass estimator, and apply both to real molecular clouds to assess gravitational boundedness.
- Derive the Jeans instability criterion and the free-fall collapse time, and apply both to real dense cores to evaluate gravitational stability and the star-formation efficiency problem.
- Derive the Stromgren-sphere ionization-balance radius and connect it to real nebular emission-line diagnostics (electron density, electron temperature, the Balmer decrement) for a real H II region.
- Derive the Rankine-Hugoniot shock-jump conditions and the cosmic-ray power-law spectrum, and synthesize shocks, cosmic rays, and magnetic fields into one multiwavelength picture of a real supernova remnant.
Textbook and Materials
Primary reading: OpenStax Astronomy 2e (free, openly licensed; local extracted reference copy under references/openstax-astronomy-2e-extracted.txt). The interstellar medium is covered in Chapter 20 ("Between the Stars: Gas and Dust in Space"): 20.1 The Interstellar Medium, 20.2 Interstellar Gas (the 21 cm line and H II regions), 20.3 Cosmic Dust (extinction and reddening), 20.4 Cosmic Rays, 20.5 The Life Cycle of Cosmic Material, and 20.6 Interstellar Matter around the Sun. This citation was cross-checked directly against Chapter 20's own embedded figure numbering (Figures 20.1–20.20 all appear under their matching section headers with no offset), rather than extrapolated by analogy from another course as in some prior curriculum courses. Because ASTR 360 is an upper-division elective, nearly every quantitative topic here (the 21 cm radiative-transfer/column-density derivation, the Jeans instability and free-fall time, the Stromgren-sphere derivation, the Rankine-Hugoniot shock-jump conditions, and the cosmic-ray power-law spectrum) goes well beyond OpenStax Astronomy 2e's introductory, descriptive treatment; each lecture's slides and notes state explicitly where this course extends beyond the assigned introductory reading.
Assessment
| Component | Weight |
|---|---|
| Problem sets (7) | 30% |
| Labs (7) | 30% |
| Midterm exam (Lectures 1–7) | 15% |
| Final exam (cumulative, emphasis Lectures 8–14) | 20% |
| Participation and reading checks | 5% |
Lecture, Lab, and Problem-Set Cadence
The course runs 14 lectures, 7 labs, and 7 problem sets — a matched 1:1 biweekly cadence in which each lab and its paired problem set both follow the same two-lecture block, following the ASTR 230/ASTR 310/ASTR 320/ASTR 340/ASTR 350 matched-cadence precedent for a standard-format 3-credit, 14-lecture course. This choice was confirmed against the actual lecture content, not assumed from file counts alone: the course is organized into seven thematic units of exactly two lectures each (ISM Phases and Energetics; the Atomic ISM and the 21 cm Line; Dust; the Molecular ISM; Star Formation; H II Regions and Ionization; Shocks, Cosmic Rays, and Magnetic Fields), and each unit's two lectures develop exactly one self-contained physical toolkit that its paired lab and problem set then apply to real data — a natural, unambiguous two-lecture-per-lab grid, following ASTR 350's precedent of choosing the matched cadence specifically because the course's thematic units are each exactly two lectures long. This is documented explicitly here, rather than left implicit, because the ISM's very wide range of sub-topics (atomic gas, dust, molecular clouds, star formation, ionized gas, shocks and cosmic rays) could in principle have been paced unevenly (as in ASTR 320's variable 2-3 lecture units); this course's seven sub-topics divide naturally into balanced two-lecture pairs, so the matched cadence was chosen deliberately rather than by default.
| Lab/PS Unit | Lectures | Lab | Problem Set | Topic | Thematic Unit |
|---|---|---|---|---|---|
| 1 | 1–2 | Lab 01 | PS 01 | ISM phase pressure balance and thermal equilibrium | Unit 1: ISM Phases and Energetics |
| 2 | 3–4 | Lab 02 | PS 02 | The 21 cm line, spin temperature, and HI column density | Unit 2: The Atomic ISM and the 21 cm Line |
| 3 | 5–6 | Lab 03 | PS 03 | Interstellar extinction, reddening, and dust emission | Unit 3: Dust |
| 4 | 7–8 | Lab 04 | PS 04 | Molecular cloud mass estimators (CO, virial) | Unit 4: The Molecular ISM |
| 5 | 9–10 | Lab 05 | PS 05 | Jeans instability and collapse timescales | Unit 5: Star Formation |
| 6 | 11–12 | Lab 06 | PS 06 | The Stromgren sphere and H II region diagnostics | Unit 6: H II Regions and Ionization |
| 7 | 13–14 | Lab 07 | PS 07 | Capstone: shocks, cosmic rays, and magnetic fields | Unit 7: Shocks, Cosmic Rays, and Magnetic Fields |
Revision Policy
High standards apply to all graded work. Problem sets and labs may be revised and resubmitted once for improved credit within one week of return, provided the resubmission includes a short change note identifying what was corrected and why (see each problem set's assessment instructions for full criteria).
Prerequisites Check
ASTR 310 (Stellar Astrophysics) and PHYS 271 (a calculus-based mechanics/electromagnetism sequence course) are required as prerequisites because this course's quantitative toolkit builds directly on tools developed in both: the radiative-transfer and Boltzmann/statistical-equilibrium reasoning used for the 21 cm line and nebular diagnostics (ASTR 310 Lectures 02–04's Planck-function, radiative-transfer, and Boltzmann/Saha derivations, directly reused here for the hyperfine population ratio and forbidden-line diagnostics), the virial theorem (ASTR 310 Lecture 06, reused here for molecular-cloud virial mass), and the general first-principles linear-perturbation-analysis habit and fluid/electromagnetic background (PHYS 271) needed to follow the Jeans-instability derivation, the Rankine-Hugoniot shock-jump conditions, and synchrotron radiation. Students who completed ASTR 310 will recognize the virial theorem and Boltzmann-factor reasoning as the same tools applied here to interstellar gas rather than stellar interiors; students arriving via PHYS 271 will recognize the linear stability analysis (Jeans instability) and the conservation-law derivation (shock jump conditions) as directly analogous to standard mechanics/fluids techniques applied here to astrophysical gas.