11. People usually use optical depth to characterize the relative ratio between measurement strength and the optical decay. 12. By measuring optical depth in SiII and CII we will estimate the covering fraction of neutral gas. 13. "' Optical depth "'in astrophysics refers to a specific level of transparency. 14. At optical depth 0.67 the radius would be, indicating an extended optically thick stellar wind. 15. In contrast, the dust bands have relatively few large particles, which results in low optical depth . 16. In the case of the WR primary star, the optical depth temperature is 96, 000 K. 17. From the definition, it is also clear that large optical depths correspond to higher rate of obscuration. 18. With an optical depth of about 0.06, it is markedly more diffuse than its companion. 19. In the case of the WR primary star, the optical depth temperature is 115, 000 K. 20. Starlight traveling through a kiloparsec column undergoes about a magnitude of extinction, so that the optical depth ~ 1.
