Differential rotation on both components of the pre-main-sequence binary system HD 155555

Nicholas James Dunstone, G. A. J. Hussain, A. Collier Cameron, S. C. Marsden, M. Jardine, J. R. Barnes, J. C. Ramirez Velez, J. -F. Donati

Research output: Contribution to journalArticlepeer-review

21 Citations (Scopus)

Abstract

We present the first measurements of surface differential rotation on a pre-main-sequence binary system. Using intensity (Stokes I) and circularly polarized (Stokes V) time-series spectra, taken over 11 nights at the Anglo-Australian Telescope (AAT), we incorporate a solar-like differential rotation law into the surface imaging process. We find that both components of the young, 18 Myr, HD 155555 (V824 Ara, G5IV + K0IV) binary system show significant differential rotation. The equator-pole lap times as determined from the intensity spectra are 80 d for the primary star and 163 d for the secondary. Similarly, for the magnetic spectra we obtain equator-pole lap times of 44 and 71 d, respectively, showing that the shearing time-scale of magnetic regions is approximately half of that found for stellar spots. Both components are therefore found to have rates of differential rotation similar to those of the same spectral-type main-sequence single stars. The results for HD 155555 are therefore in contrast to those found in other, more evolved, binary systems where negligible or weak differential rotation has been discovered. We discuss two possible explanations for this: first that at the age of HD 155555 binary tidal forces have not yet had time to suppress differential rotation and secondly that the weak differential rotation previously observed on evolved binaries is a consequence of their large convection zone depths. We suggest that the latter is the more likely solution and show that both temperature and convection zone depth (from evolutionary models) are good predictors of differential rotation strength. Finally, we also examine the possible consequences of the measured differential rotation on the interaction of binary star coronae.

Original languageEnglish
Pages (from-to)1525-1536
Number of pages12
JournalMonthly Notices of the Royal Astronomical Society
Volume387
Issue number4
Early online date5 Jun 2008
DOIs
Publication statusPublished - 11 Jul 2008

Keywords

  • binaries : spectroscopic
  • stars : coronae
  • stars : imaging
  • stars : magnetic fields
  • pre-main-sequence
  • stars : rotation
  • STELLAR SURFACE-STRUCTURE
  • DUAL-SITE OBSERVATIONS
  • ACTIVE STARS
  • MAGNETIC-FIELD
  • DOPPLER IMAGES
  • CONTACT BINARY
  • AB DORADUS
  • PATTERNS
  • EVOLUTION
  • TOPOLOGY

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