"The cause of the variability might be dust obscuration events, but it is hard to explain how you can produce and sustain obscuring dust for that long a time period."
If something (like dust) isn't blocking the light from these stars from view, could the variability be caused by internal changes in the stars? Perhaps they are coming to the end of their lives after depleting the hydrogen fuel being supplied to their cores?
"The variability might be caused by evolutionary changes occurring during shell burning flashes or helium core flashes, but these stars don't seem to be that evolved," he added.
(Helium flashes occur in intermediate mass stars when the supply of hydrogen to the internal fusion reactions of the star's core is exhausted and helium burning begins, creating a bright flash on the surface of the star.)
Simonsen also pointed out that although the behavior of these stars seems unique now, we are most likely glimpsing a short variable period in their evolution.
So by using this retroactive technique of digitizing archival photographic plates, we have been given a unique opportunity to see a portion of stellar evolution that we could only see by analyzing decades-worth of historical observations.