The long-period variable stars of M33

Infrared photometry of long-period variables (LPVs) in M33 shows that the majority of those identified up to now are supergiants. The period-luminosity relation for these stars yields a distance of M33 of 760 kpc with a 10 percent uncertainty. This uncertainty primarily reflects the uncertain distance of the Large Magellanic Cloud, although the broader P - L relation of M33 is a contributing factor. Cepheid period-luminosity relations yield a distance at the low end of this range; RR Lyrae stars tend toward the high end. The remaining LPVs are asymptotic giant branch stars. There is one confirmed carbon star among them