Spectroscopic observations of the quiescent neutron star system 4U 2129+47 (=V1727 Cygni)M. S. Bothwell, M. A. P. Torres, M. R. Garcia and P. A. CharlesA&A, 485 3 (2008) 773-775DOI: https://doi.org/10.1051/0004-6361:200809516
