[vsnet-chat 2366] Re: [vsnet-alert 3612] NGC 495 morphological type

[bas@mailhost.lowell.edu (Brian Skiff)]

     The classificiation is based on the size of the bulge and the degree
of winding of the arms.  In brief one works from "standards", basically
paradigms of the various types.  To get stage Sab, I would want to see the
arms wound about as in M81 (see your favorite photo of this), and the 
relative bulge size somewhat larger than what appears in NGC 495.  To an
extent there are no sharp boundaries and unfortunately the system is not
strictly quantitative (more well-defined systems do exist).  One could ask
the person who set up the system (de Vaucouleurs), but he's no longer with us.
A near-definitive second opinion could be obtained from someone like Harold
Corwin---I'll ask him.

\Brian

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