Magnetic field structure in single late-type giants: The weak G-band giant 37 Comae from 2008 to 2011

Abstract

This work studies the magnetic activity of the late-type giant 37 Com. This star belongs to the group of weak G-band stars that present very strong carbon deficiency in their photospheres. The paper is a part of a global investigation into the properties and origin of magnetic fields in cool giants. We use spectropolarimetric data, which allows the simultaneous measurement of the longitudinal magnetic field $B_l$, line activity indicators (H$\alpha$, Ca\,{\sc ii} IRT, S-index) and radial velocity of the star, and consequently perform a direct comparison of their time variability. Mean Stokes V profiles are extracted using the least squares deconvolution (LSD) method. One map of the surface magnetic field of the star is reconstructed via the Zeeman Doppler imaging (ZDI) inversion technique. A periodogram analysis is performed on our dataset and it reveals a rotation period of 111 days. We interpret this period to be the rotation period of 37 Com. The reconstructed magnetic map reveals that the structure of the surface magnetic field is complex and features a significant toroidal component. The time variability of the line activity indicators, radial velocity and magnetic field $B_l$ indicates a possible evolution of the surface magnetic structures in the period from 2008 to 2011. For completeness of our study, we use customized stellar evolutionary models suited to a weak G-band star. Synthetic spectra are also calculated to confirm the peculiar abundance of 37 Com. We deduce that 37 Com is a 6.5~$M_{\odot }$ weak G-band star located in the Hertzsprung gap, whose magnetic activity is probably due to dynamo action.

Accepted in A&A, 14 pages, 10 figures

References in corpus (10)

• The surprising magnetic topology of tauSco: fossil remnant or dynamo output?
• Large-scale magnetic topologies of late M dwarfs
• Weak magnetic fields in Ap/Bp stars: Evidence for a dipole field lower limit and a tentative interpretation of the magnetic dichotomy
• Comparative statistics and origin of triple and quadruple stars
• Diagnoses to unravel secular hydrodynamical processes in rotating main sequence stars
• Spectropolarimetric observations of the transiting planetary system of the K dwarf HD 189733
• The Magnetic Fields at the Surface of Active Single G-K Giants
• Magnetic confinement of the solar tachocline: II. Coupling to a convection zone
• Radial velocities for the Hipparcos-Gaia Hundred-Thousand-Proper-Motion project
• Atmospheric composition of weak G band stars: CNO and Li abundances

Cited by in corpus (3)

• Pollux: A weak dynamo-driven dipolar magnetic field and implications for its probable planet
• A decade-long magnetic monitoring of Vega
• Li-rich giant stars under scrutiny: Binarity, magnetic activity and the evolutionary status after Gaia DR2