Opacity electron scattering

L or M can then be eliminated from Eqs. (5.35) and (5.37), giving R, and hence Teff, as functions of M or L respectively. The general equations become rather messy at this point, so only two selected sets of numerical results will be given, both assuming energy generation by the CNO cycle with v = 17, Case (a) for Kramers opacity and Case (b) for electron scattering (Table 5.1). 

Given that the absorption cross-section of 07+ at the photo-ionization threshold is 10-19 cm2 and that the oxygen abundance is 10-2 by mass, find the bound-free opacity (cm2 gm-1) due to oxygen at that frequency, and compare it to the electron scattering opacity. 

The decline from the peak is relatively rapid, since the opacity of the core is determined by electron scattering. As the heavy elements recombine, this declines precipitately and the diffusion timescale rapidly becomes shorter than the dynamical timescale (see, for example, Shaeffer, Cassd and Cahen). In the radioactive tail, the luminosity can be set equal to the rate of energy generation in radioactivity (Weaver, Axelrod and Woosley, 1980) ... 

The relatively weak dependence on the ratio Ktat/ i abs suggests that the modification to our calculated results will not be great except at very early times. The effective temperature calculated for Model 10H, for example, is, without modification, within 15% of the values inferred from the spectrum (Suntzeff, private communication) on days 1.14 (13,600 K), 1.51 (12,700 K), and 1.85 (11,690 K). Figure 5 illustrates the effect for K<0 0.3, and 0.1. The latter corresponds to a color temperature one third greater than the effective emission temperature. Karp et a1. (1977) have considered the effect of Doppler broadened lines on the bound-bound opacity. For typical photospheric densities (1012 g cm-3) and temperatures (5000 K to 50,000 K) the line opacity is approximately 20% to 200% that of electron scattering (see their Table 3). This should keep the color temperature within about 20% of the effective emission temperature. 

Fig. 5 - Correction to the early visual light curve of Model 10H for the fact that the color temperature does not equal the effective emission temperature for an atmosphere whose opacity is dominantly due to electron scattering. The three curves from top to bottom have the nonconservative opacity equal to 1, 0.3, and 0.1 of the electron scattering opacity. 

Fig. 6 - Bolometric luminosities during the first 200 days for 4 of the models defined in Table 1 compared to data from Catchpole et al. (1987) and Hamuy et a1. (1987). All models employed the same 6 M helium core capped by hydrogen envelopes of various masses. The opacity, chiefly due to electron scattering while the gas remains ionized, was given a lower floor of 0.02 cm2 g-1 for elements heavier than helium.

There are a few common and long-known uses of heavy metal compounds which should be mentioned. The barium meal is used in gastrointestinal X-rays. It is administered as barium sulfate, the high electron scattering of barium ions providing X-ray opacity. Mercurial diuretics, derivatives of propan-2-ol, work by inhibition of sulfhydryl enzyme sites. These compounds are now becoming obsolete, however. 

Infrared Absorption. Attempts to determine the nature of carbon-hydrogen bonding by means of a Beckman IR-5 infrared spectrophotometer were not successful, probably because of the near opacity of the anthraxolite and excessive scatter caused by inadequate grinding. Highly graphitized carbons are commonly opaque to Infrared radiation because the absorption edge of electronic excitation occurs in the infrared range. 

---