Toroidal versus poloidal magnetic fields in Sun-like stars: a rotation threshold

By P. Petit, B. Dintrans, S. Solanki, J. Donati, M. Aurière, F. Lignières, J. Morin, F. Paletou, J. Ramirez, C. Català and 1 more. 2008

214 citations recorded by the source corpus.

From a set of stellar spectropolarimetric observations, we report the detection of surface magnetic fields in a sample of four solar-type stars, namely HD 73350, HD 76151, HD 146233 (18 Sco) and HD 190771. Assuming that the observed variability of polarimetric signal is controlled by stellar rotation, we establish the rotation periods of our targets, with values ranging from 8.8 d (for HD 190771) to 22.7 d (for HD 146233). Apart from rotation, fundamental parameters of the selected objects are very close to the Sun’s, making this sample a practical basis to investigate the specific impact of rotation on magnetic properties of Sun-like stars. We reconstruct the large-scale magnetic geometry of the targets as a low-order ( �< 10) spherical harmonic expansion of the surface magnetic field. From the set of magnetic maps, we draw two main conclusions. (i) The magnetic energy of the large-scale field increases with rotation rate. The increase in chromospheric emission with the mean magnetic field is flatter than observed in the Sun. Since the chromospheric flux is also sensitive to magnetic elements smaller than those contributing to the polarimetric signal, this observation suggests that a larger fraction of the surface magnetic energy is stored in large scales as rotation increases. (ii) Whereas the magnetic field is mostly poloidal for low rotation rates, more rapid rotators host a large-scale toroidal component in their surface field. From our observations, we infer that a rotation period lower than ≈12 d is necessary for the toroidal magnetic energy to dominate over the poloidal component.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/890444d44c007ab6c9009237214cb16735220bee

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Citations in the corpus

A BCool magnetic snapshot survey of solar-type stars (2013, methodology): “The magnetic topology of 18 Sco has previously been published (using the observations presented here) by Petit et al. (2008).”
Magnetic Fields of Nondegenerate Stars (2009, background): “A recent study focussing on main-sequence Sun-like stars with different rotation periods suggests that significant surface toroidal fields are detectd whenever the rotation period is lower than≃20 d (Petit et al. 2008a), i.e.,≃25% shorter than the rotation period of the Sun.”
Improved angular momentum evolution model for solar-like stars II. Exploring the mass dependence (2015, unknown): “…magnetic topology is indeed suggested for main-sequence stars, with solar-mass stars having more multipolar magnetic structure than lower mass stars whose magnetic topology tends to be dipole dominated (Petit et al. 2008; Donati & Landstreet 2009; Morin et al. 2010; Gregory et al. 2012).”
Large-scale magnetic topologies of late M dwarfs★: Magnetic topologies of late M dwarfs (2010, unknown): “2.1), on the derived magnetic quantities in a similar way as Petit et al. (2008).”
MAGNETIC WREATHS AND CYCLES IN CONVECTIVE DYNAMOS (2012, methodology): “Improved observational techniques including spot-tracking from Kepler photometry (Meibom et al. 2011; Llama et al. 2012) and ZeemanDoppler imaging (Petit et al. 2008; Gaulme et al. 2010; Morgenthaler et al. 2012) may permit measurements of the size, frequency, and magnetic flux of starspots and the…”
Improved angular momentum evolution model for solar-like stars (2013, background): “Solar-type magnetospheres are known to be more organized on the large-scale in slowly rotating solar-type stars than in fast rotating ones (Petit et al. 2008) and hence more efficient for wind braking.”
PERSISTENT MAGNETIC WREATHS IN A RAPIDLY ROTATING SUN (2010, background): “Recent observations of solar-type stars may indicate that even the topology of the global-scale fields changes with rotation rate, with the rapid rotators having substantial global-scale toroidal mgnetic fields at their surfaces (Petit et al. 2008).”
Stellar magnetism: empirical trends with age and rotation (2014, background): “In our sample, the maximum value of l varies from lmax ∼ 2 (e.g., for HD 76151, Petit et al. 2008) to ∼ 30 (e.g., for HD 141943, Marsden et al. 2011).”