Search for period changes in Mira stars

TL;DR

This study reobserved seven Mira variables to detect period changes over decades, revealing significant period decrease in V890 Cas and color variations in all stars, highlighting long-term stellar variability.

Contribution

It provides new long-term observational data on Mira stars, demonstrating significant period change in V890 Cas and color variations across the cycle, extending previous historical observations.

Findings

V890 Cas's period decreased by 12% from 483 to 428 days.

All stars showed color changes along their variability cycle.

Most stars exhibited smaller amplitude in recent data, likely due to improved photometric accuracy.

Abstract

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