Observations of magnetic fields on two late-type dwarf stars

Abstract

The detection of magnetic fields on the G8 V star Xi Boo A and on the K0 B star 70 Oph A is reported. A method has been developed and applied which provides estimates of the total field strength and fraction of the visible stellar surface covered by fields. The essence of this method is to perform the Fourier deconvolution of a nonmagnetically sensitive line profile from a magnetically sensitive one. This method is insensitive to magnetic field geometry and does not depend on polarization measurements. Results indicate fields of 2550 + or 390 gauss covering 20-45% Xi Boo A, and that fields of 1880 + or - 350 gauss may cover 10% of 70 Oph A. Comparison observations of solar active regions show fields of 1800 + or - 550 gauss covering 10% of the solar active regions, in line with previous work. Tests of solar quiet regions and sunspots also support the validity of the stellar measurements.