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.
Additional Information© 1990 American Astronomical Society. Received 1989 May 22; accepted 1989 July 31. We gratefully acknowledge support for this project from NSF grant 85-02518 and 87-21705. We also thank Alain Picard for assistance in obtaining the carbon star spectrum, Vance Heron and Sean Lin for help with the infrared camera, and the staff of Palomar Observatory.
Published - 1990ApJ___349__503M.pdf