Powered by Indico
v3.2.9
https://stockholmuniversity.zoom.us/j/940229961
Characteristics of surface magnetic fields of cool stars are usually established with the help of two complementary approaches. The strength and topology of global magnetic field is determined from time series polarisation measurements, typically employing cross-correlation profiles produced from thousands of spectral lines. On the other hand, an estimate of the total magnetic field strength is obtained from modelling Zeeman broadening of the intensity profiles of individual magnetically sensitive lines. For decades these two techniques were applied discordantly, using different types of observational data and yielding vastly different estimates of the global and total magnetic field strengths. The latter discrepancy is attributed to the presence of tangled magnetic fields which cancel out in polarisation observables but contribute to Zeeman broadening. Until now, the reality of this multi-scale nature of cool-star magnetic fields has not been established through a direct, self-consistent analysis. We are developing a unified magnetic field modelling framework that enables one to simultaneously derive characteristics of both global and tangled small-scale magnetic fields from the intensity and polarisation profiles of the same spectral lines. Here I will present first results of the application of this new unified magnetic retrieval approach to several strongly magnetic benchmark M dwarfs. This analysis yields mean field strengths consistent with previous Zeeman broadening studies, but, at the same time, reveals much stronger global magnetic fields compared to previous multi-line polarisation analyses of the same stars. These results have important implications for our understanding of cool-star magnetospheres and their interaction with potentially habitable exoplanets.