The long-term variation of the effective magnetic field of the active star ε Eridani

• Published in: Proceedings of the International Astronomical Union
• Main Authors: Scalia, Cesare, Leone, Francesco, Gangi, Manuele
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 2018
• Subjects: narval
• Online Access: https://doi.org/10.1017/s1743921318000959; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1743921318000959

Abstract Long-term periodicities of magnetic fields in cool stars are usually studied from activity indicators, which are only indirectly related to the presence of the field. Direct detections are complicated issues since even a complex magnetic structure, as the solar one, has a very low disk integrated magnetic signal, which is usually hidden in the noise level. We introduce a method for the direct measurement of small integrated longitudinal stellar magnetic fields (effective magnetic fields), called multi-line slope method, based on the regression of the Stokes V signal with respect to the first derivative of Stokes I. We present the results of the application of this technique to a dataset of 9 yr of observations of the active star epsilon Eridani, obtained with the spectropolarimeters Narval, HARPSpol and CAOS, showing that the long-term variation of the effective magnetic field corresponds to the period of the cycle retrieved by the activity indicators.