Inference of the magnetic field in spicules from spectropolarimetry of HeI D3

We present observations of spicules in the HeI D-3 line with full-Stokes spectropolarimetry, which were done with the Advanced Stokes Polarimeter at the Dunn Solar Telescope of the Sacramento Peak Observatory. The line profiles appear to be significantly broadened by non-thermal processes, which we interpret using the hypothesis of a distribution of velocities inside the spicule. The possibility of inferring the magnetic field in those conditions is tested on synthetic data, and the results are generalized to the interpretation of the observed data. We conclude that the magnetic field is aligned with the visible structure of the spicule, with strengths above 30 G in some cases ( for heights between 3000 and 5000 km above the photosphere).