The multi-line slope method for measuring the effective magnetic field of cool stars: an application to the solar-like cycle of ɛ Eri
Abstract
One method for the determination of integrated longitudinal stellar fields from low-resolution spectra is the so-called slope method, which is based on the regression of the Stokes V signal against the first derivative of Stokes I. Here we investigate the possibility of extending this technique to measure the magnetic fields of cool stars from high-resolution spectra. For this purpose we developed a multi-line modification to the slope method, called the multi-line slope method. We tested this technique by analysing synthetic spectra computed with the COSSAM code and real observations obtained with the high-resolution spectropolarimeters Narval, HARPSpol and the Catania Astrophysical Observatory Spectropolarimeter (CAOS). We show that the multi-line slope method is a fast alternative to the least squares deconvolution technique for the measurement of the effective magnetic fields of cool stars. Using a Fourier transform on the effective magnetic field variations of the star ɛ Eri, we find that the long-term periodicity of the field corresponds to the 2.95-yr period of the stellar dynamo, revealed by the variation of the activity index.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- December 2017
- DOI:
- 10.1093/mnras/stx2090
- arXiv:
- arXiv:1708.05196
- Bibcode:
- 2017MNRAS.472.3554S
- Keywords:
-
- polarization;
- stars: late-type;
- stars: magnetic field;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 11 pages, 8 figures, 6 tables