PCA detection and denoising of Zeeman signatures in polarised stellar spectra M. J. Martínez González, A. Asensio Ramos, T. A. Carroll, M. Kopf, J. C. Ramírez Vélez and M. Semel A&A, 486 2 (2008) 637-646 Published online: 27 May 2008 DOI: 10.1051/0004-6361:200809719