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Early successes of the theory of stellar radiative excitation of gaseous nebulae led to an expectation that the emission from all galactic gaseous nebulae could be explained in this way. One well-known object which resisted this interpretation was the Network Nebula in Cygnus, now recognized as a supernova remnant. Already by the 1930s intensive searches for an illuminating star had proven fruitless. No plausible candidate could be found and the suggestion that such an object might be hidden behind a dark cloud is not substantiated by star counts in the region.
KeywordsShock Wave Shock Front Interstellar Medium Supernova Remnant Shock Velocity
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Our discussion is hased largely on basic papers by:
- See also Spitzer, L. 1968, Diffuse Matter in Space, New York: Interscience.Google Scholar
- That the excitation of the Network Nebula was probably caused by a shock wave of velocity ~ 100 km/sec passing through the interstellar medium was suggested by J. Oort (1946, M.N.R.A.S., 106, 159). Extensive optical observational studies by E. Hubble (1937), J.W. Chamberlain (1953, Ap. J., 117, 399), R. Minkowski (1958, Rev. Mod. Phys., 30, 1048; 1968. Stars and Stellar Systems, 9), D.E. Harris (1962, Ap. J., 135, 661), S.B. Pikel’ner (1954, Crimea Obs. Publ., 12, 93), R.A. Parker (1967, Ap. J., 139, 493; 149, 363; 1969, 155, 359), A. Poveda (1965, Bol. Tonanzintla y Tacubaya, 27, 49), and J. Miller (1974, Ap. J., 189, 239) have been extended to X-ray, radio and ultraviolet regions; see, e.g., P. Benvenuti, S. D’Odorico and M.A. Dopita (1979, Nature, 277, 99), S. Rappaport et_ al. (1974, Ap. J., 194, 329), B.E. Woodgate et al. (1974, Ap. J., 188, L79). For further SNRs see, e.g., D. Osterbrock and R. Dufour (1973, Ap. J., 185, 441), N49 in LMC, D.E. Osterbrock and R. Costero (1973, Ap. J., 184, L71). Other references may be found in papers cited below.Google Scholar