SEARCH FOR PERIOD CHANGES IN MIRA STARS

We reobserved in the $R_C$ and $i'_{Sloan}$ bands, during years 2020-2021, seven Mira variables Cassiopeia, for which historical light curves were available from Asiago Observatory plates taken 1967-84. The aim was to check if any of them had undergone a substantial change period or curve shape. Very recent public data form ZTF-DR5 also used expand our time base window. A marked color detected all stars along their variability cycle. star V890 Cas showed significant decrease 12\% 483 428 days, one largest known date. All stars, save AV Cas, smaller variation amplitude CCD data, possibly due photometric accuracy higher than that photographic plates.