The datatype egg refers to Eggen's modified uvby system.
Eggen originally planned to work in the uvby system. But the width of the
v filter he got turned out to be only half of the nominal width. This
appeared to be useful for the classification of late-type stars and
Eggen defined a modified uvby system, in which the information content
of the M1 and C1 indices is different of that for the normal m1 and c1
parameters, because of the smaller width of the v filter.
The difference with the standard uvby system is indicated by the use of
upper case name for the two parameters: M1 and C1
|b-y||:||b-y colour index|
|N||:||Number of measurements|
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Last Update: 17 February 1998