de Vaucouleurs introduced several important features

de Vaucouleurs introduced several important features - de...

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de Vaucouleurs introduced several important features: (1) continuity of barred and nonbarred spirals (through mixed types SA-SAB-SB) (2) continuity of spirals into irregulars Sc-Scd-Sd-Sdm-Sm-Im (m means Magellanic, the LMC being the prototype). (3) description of the spiral structure is paramount, rather than some resolution estimate. This makes classification less sensitive to an observer's allowance for seeing or equipment changes. He introduced classes depending on whether the inner structure is ringlike or purely spiral, with mixed types recognized: (r),(rs),(sr),(s). The stage along the sequence still runs a-c (adding, in fact, stages d and m - for Magellanic types - out beyond Sc) as in the original Hubble class. For tabulation in the Reference Catalogs and convenient numerical use, a type T is often used which is -1 for S0, 0 for S0/a, on through 5 for Sc and 9 for Im. More negative values denotes various subsets of ellipticals with or without envelopes. The article by de Vaucouleurs in Handbuch der Physik (1959, 53, 275) sets out his detailed classification principles with photographic examples. (4) the notion of a ``classification volume" rather than a one dimensional sequence. The
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de Vaucouleurs introduced several important features - de...

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