Further evidence for a sub-year magnetic chromospheric activity cycle and activity phase jumps in the planet hostτBoötis

Abstract

We examine the S-index data, obtained in the context of the Mount Wilson H&K project for the nearby F-type star τ Boo, for the presence of possible cyclic variations on timescales below one year and "phase jump" episodes in the observed S-index activity levels, to determine whether such features are persistent properties of the chromospheric activity of τ Boo and possibly other late-type stars. Within the Mount Wilson H&K project τ Boo was observed during 1278 individual nights, albeit with a very inhomogeneous coverage ranging from 2 to 137 observations per year. Our analysis shows that periodical variations with timescales on the order of 110-120 days are a persistent feature of the Mount Wilson data set. Furthermore we provide further examples of "phase jump" episodes, when the observed S-index activity drops from maximum to minimum levels on timescales of one to two weeks, hence such features also appear to occur on a more or less regular basis in τ Boo.

A Radial Velocity Study of the Planetary System of Pi Mensae: Improved Planet Parameters for PI Mensae c and a Third Planet on a 125-d Orbit

“…However, shorter period activity cycles are not unprecedented for other late-type stars. Schmitt & Mittag (2017) found evidence for a ∼120-d cycle in the F6 star τ Boo. One may speculate that the 125-d RV period is roughly one-fourth of an activity cycle of ∼ 500 d and we cannot exclude this with certainty.…”

A Radial Velocity Study of the Planetary System of π Mensae: Improved Planet Parameters for π Mensae c and a Third Planet on a 125 Day Orbit

“…However, shorter-period activity cycles are not unprecedented for other late-type stars. Schmitt & Mittag (2017) found evidence for a ∼120 day cycle in the F6 star τ Boo. One may speculate that the 125 day RV period is roughly one-fourth of an activity cycle of ∼500 days, and we cannot exclude this with certainty.…”