We present a systematic analysis to determine and improve the pulsation periods of 1637 known long-period Mira variables in M33 using gri-band light curves spanning ~18yr from several surveys, including the M33 variability survey, Panoramic Survey Telescope and Rapid Response System, Palomar Transient Factory (PTF), intermediate PTF, and Zwicky Transient Facility. Based on these collections of light curves, we found that optical-band light curves that are as complete as possible are crucial to determine the periods of distant Miras. We demonstrated that the machine-learning techniques can be used to classify Miras into O-rich and C-rich based on the (J-Ks) period-color plane. Finally, We derived the distance modulus to M33 using O-rich Miras at maximum light together with our improved periods as 24.67{+/-}0.06mag, which is in good agreement with the recommended value given in the literature.

Cone search capability for table J/AJ/165/137/table2 (Observed properties of Miras in M33)