HD 4915 at the Beginning of Maunder Minimum of Activity

Abstract

Based on the available photometric data spanning almost 8000 days (21.9 years) of observations of a bright G5 V dwarf, solar-type star HD 4915, we carried out a study of the manifestations of its activity, probably transitioning to a state similar to the Maunder Minimum. To estimate the duration of the possible activity cycles of the star, we used three independent data sets. We obtained evidence of HD 4915 light variations, including the interval of time corresponding to a decrease in its chromospheric activity variations. Based on the constructed power spectrum, we can suggest the existence of possible cycles of the order of 1640 and 630 days (4.5 and 1.7 years) for the object’s brightness, which are comparable with the chromospheric activity cycle estimate of 4–4.2 years, significantly shorter than the duration of the magnetic activity cycle of the Sun, which is a distinguishing feature of HD 4915. Using photometric observations of the star from Kamogata Wide-field Survey, including data from the measurements taken after 2018, when it could have been starting an activity phase similar to the Maunder Minimum, we obtained indications of possible 450, 1260 and 2000 day cycles (1.23, 3.5 and 5.5 years) and made a conclusion about the presence of cyclic light variations during this supposed lower activity state of HD 4915. We discuss the probable estimate of the star’s rotation period. A consideration of the HD 4915 data available in the TESS archive for four observing sets led us to conclude that they are unsuitable for determining its rotation period.