Résumé
With the spectropolarimeter Narval at TBL we have initiated in spring 2015 a 2-year campaign dedicated to a sample of cool and evolved stars including pulsating RV Tauri stars. We monitor net circular and linear polarisation in the spectral lines of R Scuti, the brightest of such variable targets. Our aim is to study the surface magnetic field and the linear polarisation associated with specific spectral lines. We confirm a definite detection of the surface magnetic field of R Sct, with an average longitudinal component {B_ℓ = 0.9 ± 0.5 G}. We also unveil our first results on linear polarisation.