TY - JOUR

T1 - Magnetic field structure in single late-type giants

T2 - The weak G -band giant 37 Comae from 2008 to 2011

AU - Tsvetkova, S.

AU - Petit, P.

AU - Konstantinova-Antova, R.

AU - Aurière, M.

AU - Wade, G. A.

AU - Palacios, A.

AU - Charbonnel, C.

AU - Drake, N. A.

PY - 2017/3/1

Y1 - 2017/3/1

N2 - Aims. 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. Methods. We use spectropolarimetric data, which allows the simultaneous measurement of the longitudinal magnetic field Bl, line activity indicators (Hα, Ca 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. Results. 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 Bl 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. Conclusions. We deduce that 37 Com is a 6.5 Mθ weak G-band star located in the Hertzsprung gap, whose magnetic activity is probably due to dynamo action.

AB - Aims. 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. Methods. We use spectropolarimetric data, which allows the simultaneous measurement of the longitudinal magnetic field Bl, line activity indicators (Hα, Ca 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. Results. 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 Bl 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. Conclusions. We deduce that 37 Com is a 6.5 Mθ weak G-band star located in the Hertzsprung gap, whose magnetic activity is probably due to dynamo action.

KW - Dynamo

KW - Stars: abundances

KW - Stars: activity

KW - Stars: evolution

KW - Stars: individual: 37 Comae

KW - Stars: magnetic field

UR - http://www.scopus.com/inward/record.url?scp=85014761902&partnerID=8YFLogxK

U2 - 10.1051/0004-6361/201527034

DO - 10.1051/0004-6361/201527034

M3 - Article

AN - SCOPUS:85014761902

VL - 599

JO - ASTRONOMY & ASTROPHYSICS

JF - ASTRONOMY & ASTROPHYSICS

SN - 0004-6361

M1 - A72

ER -