R Aurigae is a fine, bright, long-period Mira variable that's been well-observed by the amateur community for well over a century. It's period of 450 days is high for the optically bright Miras, but periods can be much longer for some of the dust-enshrouded Miras and pulsating OH/IR stars. R Aurigae shows rather extreme examples of behavior common to nearly all Mira variables, namely their cycle-to-cycle variations. Some classes of pulsating stars like Cepheids and RR Lyrae stars don't change much from cycle-to-cycle unless there are multiple pulsation periods present in the star at the same time. Most Mira variables aren't stable from cycle to cycle. Some stars show small waves and jitter in their light curves, while others like R Aurigae look like a completely different star from one cycle to another. And in this case at least, it's not due to additional pulsation periods in the star, at least not ones that we've detected. Long term period changes in R Aurigae have been investigated, but the evidence thus far is weak. Keep watching, and perhaps we'll find out!
Prepared By: Matthew Templeton