Long-Period Variability in o Ceti

TL;DR

This study analyzed over a century of light curve data for o Ceti to search for long secondary periods and long-term period variations, finding no evidence for coherent long secondary periods but detecting stochastic low-frequency variability similar to red noise spectra.

Contribution

It provides the first comprehensive long-term analysis of o Ceti's variability, revealing stochastic low-frequency noise without evidence of coherent long secondary periods.

Findings

No coherent long secondary periods detected in o Ceti.

Detected low-frequency stochastic variability similar to red noise spectra.

Marginal evidence of slight pulsation period modulation.

Abstract

We carried out a new and sensitive search for long-period variability in the prototype of the Mira class of long-period pulsating variables, o Ceti (Mira A), the closest and brightest Mira variable. We conducted this search using an unbroken light curve from 1902 to the present, assembled from the visual data archives of five major variable star observing organizations from around the world. We applied several time-series analysis techniques to search for two specific kinds of variability: long secondary periods (LSPs) longer than the dominant pulsation period of ~333 days, and long-term period variation in the dominant pulsation period itself. The data quality is sufficient to detect coherent periodic variations with photometric amplitudes of 0.05 mag or less. We do not find evidence for coherent LSPs in o Ceti to a limit of 0.1 mag, where the amplitude limit is set by intrinsic, stochastic, low-frequency variability of approximately 0.1 mag. We marginally detect a slight modulation of the pulsation period similar in timescale to that observed in the Miras with meandering periods, but with a much lower period amplitude of +/-2 days. However, we do find clear evidence of a low-frequency power-law component in the Fourier spectrum of o Ceti's long-term light curve. The amplitude of this stochastic variability is approximately 0.1 mag at a period of 1000 days, and it exhibits a turnover for periods longer than this. This spectrum is similar to the red noise spectra observed in red supergiants.