"Color Reversal" and Uxor definition

American Association of Variable Star Observers (AAVSO)
Fri, 08/20/2021 - 15:52

Regarding UXORs.  The first reference to UXOR’s in the VSX variable type page is in the context of the ISA group.  It is written as if the two types are synonymous and leaves the impression that UXORs are always spectral type B and A stars.  Later there is a dedicated description of UXORs that is more detailed.  It would seem that not all UXORs are ISA stars and vice versa, and hence gratuitously confusing to conflate the two types when characterizing ISA stars beyond perhaps noting that some stars are both. 

That aside, the more fulsome definition of UXORs refers to a “color reversal” that occurs at minimums.  Can someone elaborate on what this means and if you know of a more detailed rundown on the defining characteristics of UXORs, I would appreciate a reference as I have a number of candidates.