Work

Evolution of the Magnetic Activity of the Single Giant OP Andromedae Between 1993 and 2025

Year: 2025

Type: article

Abstract: We investigate the long-term magnetic variability of OP And, a magnetically active single K giant, between 1993 and 2025. To track magnetic activity, we analyze the variability of the Hα line and two lines of the calcium infrared triplet. The variability of the Hα line reveals that the activity level of OP And is higher in the period 1993–2000, while during the period 2010–2016 it is lower, possibly close to an eventual minimum. Recent data (2020–2025) indicate an increase of the activity level again. The flare frequency rate and the calcium infrared triplet data (when available) follow the same behavior. In addition, the structure of the Hα line also changes with the activity level: when the activity is higher, we observe a blue-shifted component of this line, interpreted as an expanding hot area above the photosphere, but during the lower activity interval it is almost absent. Our results are in a good agreement with the idea that the magnetic field influences the mass outflow in this giant. Additionally, we examine how flare frequency correlates with overall activity. While a complete activity cycle remains undetermined, the recent upward trend suggests that the eventual activity cycle of OP And seems to be slightly longer than 30 years. More years of observations are necessary to reach the next maximum and to determine the exact duration of the cycle.

Source: Universe

DOI: 10.3390/universe11120399