X-ray emission from the luminous O-type subdwarf HD 49798 and its compact companion S. Mereghetti, N. La Palombara, A. Tiengo, N. Sartore, P. Esposito, G. L. Israel and L. Stella A&A, 553 (2013) A46 Published online: 30 April 2013 DOI: 10.1051/0004-6361/201321271