Magnetic field and chromospheric activity evolution of HD75332: a rapid magnetic cycle in an F star without a hot Jupiter

TL;DR

This study investigates the magnetic activity and potential rapid magnetic cycle of the F7V star HD75332 over 53 years, revealing a possible 1.06-year cycle similar to the Sun's, and compares it to the rapid cycle of τ Boo, suggesting such cycles may be common in late-F stars.

Contribution

The paper presents long-term chromospheric and magnetic field observations of HD75332, identifying a rapid magnetic cycle and comparing it to τ Boo, thus providing insights into stellar dynamos in late-F stars without hot Jupiters.

Findings

HD75332 exhibits a ~1.06-year magnetic cycle.

Magnetic field reversals align with chromospheric activity maxima.

Rapid magnetic cycles may be common in late-F stars.

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 $\tau$ 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. ${\tau}$ Boo has a rapid $\sim$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 ${\tau}$ Boo and its hot Jupiter. To shed light on this, we studied the magnetic activity of HD75332 (F7V) which has similar physical properties to ${\tau}$ Boo and does not appear to host a hot Jupiter. We characterized its long term chromospheric activity variability over 53 yrs 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 HD75332 has a rapid $\sim$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 ${\tau}$ Boo, suggesting that rapid magnetic cycles may be intrinsic to late-F stars and related to their shallow convection zones.