The relation between stellar magnetic field geometry and chromospheric activity cycles - II The rapid 120-day magnetic cycle of τ Bootis

S. V. Jeffers*, M. Mengel, C. Moutou, S. C. Marsden, J. R. Barnes, M. M. Jardine, P. Petit, J. H. M. M. Schmitt, V. See, A. A. Vidotto, BCool Collaboration

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

38 Citations (Scopus)

Abstract

One of the aims of the BCool programme is to search for cycles in other stars and to understand how similar they are to the Sun. In this paper, we aim to monitor the evolution of τ Boo's large-scalemagnetic field using high-cadence observations covering its chromospheric activity maximum. For the first time, we detect a polarity switch that is in phase with τ Boo's 120-day chromospheric activity maximum and its inferred X-ray activity cycle maximum. This means that τ Boo has a very fast magnetic cycle of only 240 days. At activity maximum τ Boo's large-scale field geometry is very similar to the Sun at activity maximum: it is complex and there is a weak dipolar component. In contrast, we also see the emergence of a strong toroidal component which has not been observed on the Sun, and a potentially overlapping butterfly pattern where the next cycle begins before the previous one has finished.

Original languageEnglish
Pages (from-to)5266-5271
Number of pages6
JournalMonthly Notices of the Royal Astronomical Society
Volume479
Issue number4
Early online date5 Jul 2018
DOIs
Publication statusPublished - 1 Oct 2018

Keywords

  • Stars: activity
  • Stars: individual: (τ Boo)
  • Stars: magnetic field
  • Stars: solar-type
  • Starspots
  • Techniques: polarimetric

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