Zheleznyak, A.P.2011-10-042011-10-042009Zheleznyak A.P. Globular Cluster M15: New Variable Stars / A.P. Zheleznyak // Institute of Astronomy of Kharkiv V. N. Karazin National University. – Kharkiv, 2009. – P. 41 – 43https://ekhnuir.karazin.ua/handle/123456789/4684englobular cluster M15Article