Follow-up observations of X-ray emitting hot subdwarf stars: the He-rich sdO BD +37° 1977 N. La Palombara, P. Esposito, S. Mereghetti, G. Novara and A. Tiengo A&A, 580 (2015) A56 Published online: 03 August 2015 DOI: 10.1051/0004-6361/201526141