XMM-Newton RGS spectrum of RX J0720.4-3125: an absorption feature at 0.57 keV V. Hambaryan, R. Neuhäuser, F. Haberl, M. M. Hohle and A. D. Schwope A&A, 497 1 (2009) L9-L12 Published online: 11 March 2009 DOI: 10.1051/0004-6361/200811378