Magnetic field and chromospheric activity evolution of HD 75332: a rapid magnetic cycle in an F star without a hot Jupiter

Abstract

Studying cool star magnetic activity gives an important insight into the stellar dynamo and its relationship with stellar properties, as well as allowing us to place the Sun’s magnetism in the context of other stars. Only 61 Cyg A (K5V) and τ Boo (F8V) are currently known to have magnetic cycles like the Sun’s, where the large-scale magnetic field polarity reverses in phase with the star’s chromospheric activity cycles. τ Boo has a rapid ∼240 d magnetic cycle, and it is not yet clear whether this is related to the star’s thin convection zone or if the dynamo is accelerated by interactions between τ Boo and its hot Jupiter. To shed light on this, we studied the magnetic activity of HD 75332 (F7V) which has similar physical properties to τ Boo and does not appear to host a hot Jupiter. We characterized its long-term chromospheric activity variability over 53 yr and used Zeeman Doppler Imaging to reconstruct the large-scale surface magnetic field for 12 epochs between 2007 and 2019. Although we observe only one reversal of the large-scale magnetic dipole, our results suggest that HD 75332 has a rapid ∼1.06 yr solar-like magnetic cycle where the magnetic field evolves in phase with its chromospheric activity. If a solar-like cycle is present, reversals of the large-scale radial field polarity are expected to occur at around activity cycle maxima. This would be similar to the rapid magnetic cycle observed for τ Boo, suggesting that rapid magnetic cycles may be intrinsic to late-F stars and related to their shallow convection zones.

The winds of young Solar-type stars in Coma Berenices and Hercules-Lyra

“…This is supported by the study of Hussain et al ( 2000 ), which found similar results using different ZDI implementations. Polarity reversals have been observed for the stars τ Bo ötis (Donati et al 2008 ;Fares et al 2009Fares et al , 2013Mengel et al 2016 ) and HD 75332 (Brown et al 2021 ). Evidence of field reversals in HD 78366 and HD 190771 was found by Morgenthaler et al ( 2011 ); the authors also found evidence of a more complex cycle in ξ Bo ötis A.…”

The winds of young Solar-type stars in Coma Berenices and Hercules-Lyra

“…This is supported by the study of Hussain et al (2000), which found similar results using different ZDI implementations. Polarity reversals have been observed for the stars 𝜏 Boötis (Donati et al 2008;Fares et al 2009Fares et al , 2013Mengel et al 2016) and HD 75332 (Brown et al 2021). Evidence of field reversals in HD 78366 and HD 190771 was found by Morgenthaler et al (2011); the authors also found evidence of a more complex cycle in 𝜉 Boötis A.…”

The winds of young Solar-type stars in the Hyades

“…The ability of ZDI to resolve the large-scale field is supported by observations of polarity reversals, presumably as part of a stellar magnetic cycle. Observations of the same star at different epochs have shown periodic polarity reversals in the stars 𝜏 Boötis (Donati et al 2008;Fares et al 2009Fares et al , 2013Mengel et al 2016) and HD75332 (Brown et al 2021); Morgenthaler et al (2011) found evidence of field reversals in HD 78366 and HD 190771, and a more complex cycle in 𝜉 Boötis A. We consider the effect of magnetic cycles on this work in Section 5.5.…”