The cycles of activity similar to the solar one are thought to exist in other stars with outer convection zones. The long‐term monitoring of magnetic cycles in stars similar in structure to the Sun is a main diagnostic method for understanding how dynamo generation and amplification of magnetic fields occur. We have performed a search for solar‐like magnetic activity on the yellow subgiant β Aql. Direct measurements of the longitudinal magnetic field of β Aql were performed by measuring the Zeeman splitting in spectral lines, using the circularly polarized spectra obtained at the Crimean Astrophysical Observatory over 51 nights during 1997–2015. The magnetic field on β Aql was detected with the confidence level above 3σ over 24 nights. The activity cycle of β Aql was found to be 969 ± 27 days. We assume that the activity of β Aql is similar to that of stars younger than the Sun. The most probable rotation period was found to be Prot = 5.08697 ± 0.00031 days. Assuming the global magnetic field of β Aql as a dipole, we estimated the polar field strength Bpol = 24 G, the angle between the rotation axis and the line of sight i = 25°, and the angle between the rotation and dipole axes β = 96°.

Features of the development of activity cycles in the solar-type stars and fast-rotating cool dwarfs have been considered for 65 stars observed in some decades. Cycles with duration of 7-18 years compared to the solar cycle were found for about 50% of the studied stars. In cooler dwarfs with rotation periods of less than 5 days, cyclic changes in brightness occur on longer scales, up to 80 years. Activity of the highest level is produced on K dwarfs; their main cycles are long and have the highest amplitudes. Both old and young solar-type stars show a similar tendency in increasing the cycle length with a slower rotation. No evidence for a relation between the rotation period and duration of cycles was found for cool dwarfs with P rot < 5 days.

No abstract

The diagram of indices of coronal and chromospheric activity allowed us to reveal stars where solar-type activity appears and regular cycles are forming. Using new consideration of a relation between coronal activity and the rotation rate, together with new data on the ages of open clusters, we estimate the age of the young Sun corresponding to the epoch of formation of its cycle. The properties of the activity of this young Sun, with an age slightly older than one billion years, are briefly discussed. An analysis of available data on the long-term regular variability of late-type stars leads to the conclusion that duration of a cycle associated with solar-type activity increases with the deceleration of the stellar rotation; i.e., with age. New data on the magnetic fields of comparatively young G stars and changes in the role of the large-scale and the local magnetic fields in the formation of the activity of the young Sun are discussed. Studies in this area aim to provide observational tests aimed at identifying the conditions for the formation of cyclic activity on stars in the lower part of the main sequence, and test some results of dynamo theory.

We use original spectra and available photometric data to recover parameters of the stellar atmosphere of PZ Mon, formerly referred as an active red dwarf. The derived effective temperature T ef f =4700 K and gravity log g=2.8 suggest that PZ Mon is a K2III giant. Stellar atmosphere parameters (T ef f and log g) alongside with the evolutionary tracks are used to estimate the stellar mass of ≈ 1.5 M ⊙ and the radius of ≈ 7.7 R ⊙ . The angular radius derived by the infrared flux method when combined with the linear radius suggests the distance of 250 ± 70 pc, a factor 2.5 smaller than that suggested by the Hipparcos parallax. The red giant status of PZ Mon is confirmed by the carbon and nitrogen abundance. The spectrum reveals pronounced Heı 5876Å absorption and Hα emission indicating the robust chromosphere. The IUE spectrum is found to contain transition layer emission line of C iv 1550Å. The C iv and Xray luminosities turn out typical of RS CVn stars. The extended set of available photometric data confirms the period of 34.14 days presumably related to the stellar rotation. We found variations of the radial velocity with the amplitude of ≈ 8 km s −1 which could be caused by the orbital motion.