# ASTR 360 Reference Log

Tracks references, datasets, and visuals used in ASTR 360 materials, their verification status, and any human spot-check requirements. Provenance is labeled at one of three explicit levels throughout: **(1) live-verified this session** (fetched/extracted from a primary or authoritative source during this course's production), **(2) standard published/literature value not re-verified this session** (flagged for human spot-check), or **(3) synthetic/instructor-provided/illustrative placeholder**.

## Textbook

- OpenStax Astronomy 2e (openly licensed; local extracted copy `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/reddening), 20.4 Cosmic Rays, 20.5 The Life Cycle of Cosmic Material, 20.6 Interstellar Matter around the Sun. **This chapter/section numbering was cross-checked directly against the local extracted text's own embedded figure numbering this session** (Figures 20.1 through 20.20 all appear under their correctly matching section headers, with no offset), so this citation is directly verified against the local text, not extrapolated by analogy from a prior course as some earlier courses in this curriculum required. Nearly every quantitative ASTR 360 topic (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) is **not covered at the introductory level in OpenStax Astronomy 2e at all** and is developed here from first principles instead.

## Real Data Used in Lectures/Labs/Problem Sets

| Dataset | Used in | Source | Verification Level |
|---|---|---|---|
| Six ISM phase parameters (n, T, P/k, filling factor) for molecular clouds, CNM, WNM, WIM, H II regions, HIM | Lectures 01-02; Lab 01; PS 01 | McKee & Ostriker (1977), *ApJ* 218, 148; Draine (2011), *Physics of the Interstellar Medium* textbook Table 1.1; Ferriere (2001), *Rev. Mod. Phys.* 73, 1031 | **Level 2: standard published, not independently re-verified this session.** |
| 21 cm hyperfine transition frequency (1420.405751 MHz) and CNM/WNM spin temperatures (100 K / 8000 K) and characteristic linewidths | Lectures 03-04; Lab 02; PS 02 | The 21 cm frequency is an exact, defined atomic constant. CNM/WNM T_spin and linewidths: Kalberla & Kerp (2009), *ARA&A* 47, 27 review | **Level 2 (T_spin/linewidth values) / exact defined constant (21 cm frequency itself).** |
| 3C 273 sightline HI column density (1.79e20 cm^-2) and Cygnus X-1 sightline column density (6.0e21 cm^-2) | Lecture 04; Lab 02; PS 02 | HI4PI Collaboration (2016), *A&A* 594, A116 (3C 273); X-ray spectral absorption studies, e.g. Miller et al. (2009), *ApJ* 697, 900 and Ng et al. (2019), *MNRAS* 482, 5265 (Cygnus X-1) | **Level 2: standard published, not independently re-verified this session.** |
| Representative synthetic two-component (CNM+WNM) 21 cm brightness-temperature spectrum shape (peak T_B values) used in Lecture 04's and Lab 02's worked column-density integration | Lecture 04; Lab 02 | This course's own illustrative construction, calibrated to real T_spin and linewidth values but not a fit to one specific published sightline's spectrum | **Level 3: synthetic/illustrative placeholder, explicitly disclosed in the lecture and lab text as representative, not a claimed measurement of any single real sightline.** |
| Cardelli, Clayton & Mathis (1989) average diffuse-ISM extinction-curve parametrization (R_V=3.1) | Lectures 05-06; Lab 03; PS 03 | Cardelli, Clayton & Mathis (1989), *ApJ* 345, 245 | **Level 2: standard published, not independently re-verified this session.** |
| Cygnus OB2 No. 12: E(B-V)=3.10 mag, R_V=3.0 | Lecture 05; Lab 03; PS 03 | Massey & Thompson (1991), *AJ* 101, 1408; Maryeva & Chentsov (2012) spectroscopic study | **Level 2: standard published, not independently re-verified this session.** |
| HD 200775 (NGC 7023 illuminating star): E(B-V)=0.53 mag, R_V=5.0 (anomalous dense-cloud extinction sightline) | Lectures 05-06; Lab 03; PS 03 | Whittet et al. (2001), *A&A* 368, 1140 | **Level 2: standard published, not independently re-verified this session.** |
| X_CO conversion factor (2.0e20 cm^-2 (K km/s)^-1) | Lectures 07-08; Lab 04; PS 04 | Bolatto, Wolfire & Leroy (2013), *ARA&A* 51, 207 | **Level 2: standard published, not independently re-verified this session.** |
| Orion Molecular Cloud (OMC-1 ridge): mass~2000 Msun, radius~1.0 pc, n(H2)~1e5 cm^-3, T~25 K, CO FWHM~3.0 km/s | Lectures 07-08; Labs 04-05; PS 04-05 | Genzel & Stutzki (1989), *ARA&A* 27, 41; Bally (2008), "Overview of the Orion Complex," Handbook of Star Forming Regions | **Level 2: standard published, not independently re-verified this session.** |
| Taurus Molecular Cloud: mass~1.5e4 Msun, radius~6.0 pc, n(H2)~3e2 cm^-3, T~10 K, CO FWHM~1.5 km/s, distance~140 pc | Lecture 08; Lab 04; PS 04 | Goldsmith et al. (2008), *ApJ* 680, 428 (COMPLETE survey); Galli et al. (2018), *ApJ* 859, 33 (Gaia DR2 distance) | **Level 2: standard published, not independently re-verified this session.** |
| OMC-1 dense core: n(H2)~1e5 cm^-3, T~20 K (representative dense-core values, not individually mass-measured in this course's dataset) | Lectures 09-10; Lab 05; PS 05 | Bergin & Tafalla (2007), *ARA&A* 45, 339, "Cold Dark Clouds" review | **Level 2: standard published, not independently re-verified this session.** |
| Barnard 68: n(H2)~8e4 cm^-3, T~10 K, mass=2.1 Msun, radius=0.06 pc, distance=125 pc | Lectures 09-10; Lab 05; PS 05 | Alves, Lada & Lada (2001), *Nature* 409, 159 (near-infrared extinction mapping) | **Level 2: standard published, not independently re-verified this session.** |
| Orion Nebula (M42): distance=414 pc; ionizing star theta1 Orionis C, spectral type O7V, T_eff~39,000 K, Q_H=1.0e49 photons/s; nebular n_e~600 cm^-3, T_e~1e4 K; observed radius~0.6 pc | Lectures 11-12; Lab 06; PS 06 | Menten et al. (2007), *A&A* 474, 515 (distance); Simon-Diaz et al. (2006), *A&A* 448, 351 (stellar parameters); Vacca, Garmany & Shull (1996), *ApJ* 460, 914 and Martins, Schaerer & Hillier (2005), *A&A* 436, 1049 (Q_H calibration); Baldwin et al. (1991), *ApJ* 374, 580; Osterbrock & Ferland (2006) textbook (n_e, T_e) | **Level 2: standard published, not independently re-verified this session.** |
| Case B recombination coefficient at T_e=1e4 K (2.59e-13 cm^3/s) | Lectures 11-12; Lab 06; PS 06 | Osterbrock & Ferland (2006), *Astrophysics of Gaseous Nebulae and Active Galactic Nuclei* textbook | **Level 2: standard published atomic-physics constant, not independently re-verified this session.** |
| Rosette Nebula: distance=1600 pc, ionizing cluster NGC 2244, Q_H=6.0e49 photons/s, n_e~15 cm^-3, observed radius~10 pc | Lecture 11; PS 06 | Celnik (1985), *A&AS* 60, 465 and later radio/optical studies (summary values) | **Level 2: standard published, not independently re-verified this session.** |
| Cassiopeia A: distance=3400 pc, age~350 yr, shock velocity=5000 km/s | Lectures 13-14; Lab 07; PS 07 | Vink (2004), *ApJ* 604, 176 and subsequent Chandra proper-motion studies | **Level 2: standard published, not independently re-verified this session.** |
| Tycho's SNR (SN 1572): distance=2500 pc, age=454 yr, shock velocity=4600 km/s | Lecture 13; PS 07 | Williams et al. (2016), *ApJ* 823, 32 and refs. therein | **Level 2: standard published, not independently re-verified this session.** |
| Electron-ion temperature non-equilibration at fast collisionless shocks (observed X-ray/electron temperatures well below the Rankine-Hugoniot ion-temperature prediction for young, fast remnants like Cas A and Tycho) | Lecture 13; Lab 07; PS 07 | Ghavamian, Laming & Rakowski (2007), *ApJ* 654, L69 | **Level 2: standard published, not independently re-verified this session.** This is the physically correct, honest resolution of an apparent factor-of-~10 discrepancy between this course's computed ion temperature (kT2~25-30 keV) and the few-keV electron temperatures Chandra actually observes; see "Corrections Made During Production" below. |
| Particle Data Group cosmic-ray differential flux parametrization (J~1.8e4 (E/1 GeV)^-2.7 nucleons/(m^2 s sr GeV) below the ~3e15 eV knee, steepening to E^-3.1 above it) | Lecture 14; Lab 07; PS 07 | Workman et al. (2022) (Particle Data Group), *Prog. Theor. Exp. Phys.* 083C01, "Cosmic Rays" review | **Level 2: standard published, not independently re-verified this session.** |
| Galactic-average ISM magnetic field (~6 microG) and the Crutcher (2012) molecular-cloud Zeeman B-n scaling (B0=10 microG below n_crit=300 cm^-3, B proportional to n^0.65 above it) | Lecture 14; Lab 07; PS 07 | Beck (2001), *Space Sci. Rev.* 99, 243; Crutcher (2012), *ARA&A* 50, 29, "Magnetic Fields in Molecular Clouds" | **Level 2: standard published, not independently re-verified this session.** |
| Crab Nebula synchrotron-emitting magnetic-field strength (~3e-4 G, equipartition estimate) | Lecture 14; Lab 07; PS 07 | Hester (2008), *ARA&A* 46, 127 review | **Level 2: standard published, not independently re-verified this session.** |

## Corrections Made During Production

- **Cassiopeia A / Tycho shock post-shock temperature -- ion vs. electron temperature (Lecture 13, Lab 07, PS 07):** the Rankine-Hugoniot strong-shock formula applied to Cas A's and Tycho's real published shock velocities predicts post-shock temperatures of kT2~25-30 keV. An early draft characterized this as "broadly consistent with" the few-keV X-ray temperatures Chandra actually observes from these remnants, which is a genuine, order-of-magnitude overclaim (the predicted ion temperature is roughly ten times the observed electron temperature). This was caught during this session's own internal consistency check (comparing the computed kT2 values against the well-known real few-keV Chandra spectroscopic results for these two remnants) and corrected to state the honest, physically correct explanation: the jump-condition formula predicts the post-shock *ion* temperature, and fast, young, collisionless shocks like Cas A's and Tycho's are well documented to have incomplete electron-ion temperature equilibration (Ghavamian, Laming & Rakowski 2007), so the much lower observed X-ray (electron) temperature is expected physics, not a computational error or a failure of the jump conditions. This is exactly the class of "honest characterization of an approximation-vs-reality discrepancy" the course-materials-review skill requires catching, and it was caught and corrected before this course's first review pass rather than during it.
- **OMC-1 direct vs. CO-derived mass factor (Lecture 07, Lab 04):** the direct (density x volume x mu_molecular m_H) and CO-derived (X_CO-based, with its conventional factor-of-2 H2-molecule accounting) mass estimates for OMC-1 differ by about 17%, attributable to the direct method's explicit helium mean-molecular-weight correction (mu=2.33) versus the CO method's simpler factor-of-2 convention. This is disclosed explicitly in Lecture 07's text as an honest methodological discrepancy between two real, legitimate mass-estimation conventions, not presented as an exact agreement.
- **Orion Nebula and Rosette Nebula Stromgren-radius vs. observed-radius discrepancies (Lecture 11, Lab 06, PS 06):** the idealized single-star, uniform-density Stromgren-sphere model over-predicts Orion's radius by roughly 60% and Rosette's by roughly 100% relative to each nebula's real observed size. Both lectures and the corresponding lab/problem-set state this discrepancy explicitly and attribute it to genuine, disclosed physical limitations of the idealized model (non-uniform density, density-bounded rather than ionization-bounded geometry, multiple ionizing stars), not to a computational error, following the ASTR310 precedent of honestly characterizing approximation-vs-reality gaps rather than mischaracterizing them as close agreement.

## Visuals

Lecture-specific SVG diagrams are generated programmatically per lecture (see `src/generate_astr360_content.py`), including a log density-temperature ISM phase diagram, a schematic thermal-equilibrium S-curve, a 21 cm hyperfine energy-level diagram with a population-ratio curve, a two-component HI brightness-temperature spectrum, a Cardelli extinction curve with two real reddened stars marked, a modified-blackbody dust-emission SED, a three-method molecular-cloud mass comparison bar chart, a Larson's-law size-linewidth scatter plot, a Jeans-mass-vs-density curve, a free-fall-time-vs-density curve, a Stromgren-radius-vs-electron-density curve, a schematic ionization-fraction radial profile, a shock-compression-ratio-vs-Mach-number curve, and a cosmic-ray differential-flux spectrum. All are schematic/explanatory rather than photographic, so no external image licensing is required. Every lecture's visual-reasoning figure is a structurally distinct diagram type, verified via a mechanical grep-based check for repeated SVG coordinate/shape signatures across all 14 lecture files (only the shared header rectangle/title text block repeats, as expected -- the actual data-plot content of every figure is distinct).

## Human Spot-Check Checklist Before Instructional Use

- [ ] Confirm the six ISM phase parameters against McKee & Ostriker (1977) and/or a current review (e.g., Ferriere 2001; Draine 2011).
- [ ] Confirm the 3C 273 and Cygnus X-1 HI column densities directly against the HI4PI survey and current X-ray spectral-fitting literature.
- [ ] Confirm Cygnus OB2 No. 12's and HD 200775's E(B-V)/R_V values directly against Massey & Thompson (1991) and Whittet et al. (2001) respectively.
- [ ] Confirm the Orion and Taurus Molecular Cloud parameters directly against Genzel & Stutzki (1989)/Bally (2008) and Goldsmith et al. (2008) respectively.
- [ ] Confirm Barnard 68's mass/size directly against Alves, Lada & Lada (2001).
- [ ] Confirm theta1 Orionis C's ionizing-photon rate and the Orion Nebula's n_e/T_e directly against Vacca, Garmany & Shull (1996)/Martins, Schaerer & Hillier (2005) and Baldwin et al. (1991) respectively.
- [ ] Confirm the Cassiopeia A and Tycho shock velocities directly against Vink (2004) and Williams et al. (2016) respectively.
- [ ] Confirm the PDG cosmic-ray flux parametrization against the current Particle Data Group Review of Particle Physics edition.
- [ ] Confirm the Crutcher (2012) B-n scaling coefficients and the Crab Nebula field strength against the primary literature.
- [ ] Verify exact OpenStax Astronomy 2e Chapter 20 section/page numbers against the adopted edition (this session's own extracted-text figure-numbering cross-check found no offset, but the adopted print/online edition should still be spot-checked).

Last updated: 2026-09-25