ASTRONOMY 216 OUTLINE -- WIM CARL HEILES -------------------------- WIM --------------------------------- reading: Haffner et al review. heilesreview-final-preprint.pdf for scattering: the SINS book, in particular heiles/stinebring review, section 4. astroph ***** 1. Historical info: low-freq sky from tasmania pulsar dispersion WHAM - H alpha emission interstellar scattering of radio waves 2. H alpha gives EMs and also the total power requirement for WIM ionization directly. by elimination, it must be UV photons from stars. power requirement in inner Galaxy is 60X higher than near the Sun. 3. Pulsar dispersion. Basic results. The Dispersion Measure DM 4. filling factors and electron densities from DM and EM, both perp and parallel to Galactic plane. 5. T determinaation from forbidden lines. WIM hotter than standard HII regions, and T increases as n_e decreases. Suggests a new heating mechanism. Dust? Cosmic rays? 6. Combine the in-plane pulsar DMs, the in-plane Halpha EMs, the 'perp' Dms and EMs, and the assumption of an exponential z distribution for WIM density to derive the scale height, mean electron density, clump filling factor, the true electron density. 7. The Taylor/Cordes and Cordes/Lazio models of WIM in the Galaxy. 10. Interstellar DIFFRACTIVE scattering and scintillation. Electron fluctuations. AU size scales. Arcs and Arclets. Intra-Day and Intra/Hour variables. 11. The Scattering Measure SM. 12. Exterme Scattering Events (ESEs) and refractive scattering. 13. WIM (DIG) in External Galaxies