An extreme-AO search for giant planets around a white dwarf - VLT/SPHERE performance on a faint target GD 50S. Xu, S. Ertel, Z. Wahhaj, J. Milli, P. Scicluna and G. H.-M. BertrangA&A, 579 (2015) L8DOI: https://doi.org/10.1051/0004-6361/201526179