Data sources:

6m: Direct images taken with the Russian 6 m BTA telescope and SCORPIO spectral camera.
AA,gl,gy: E.A.Gladyshev, Astron.Zirkular No. 1138, 1980; E.A.Gladyshev, V.P.Goranskij, N.E.Kurochkin, A.M.Cherepashchuk, Astron. Zirkular No. 1145, 1980; S.A.Gladyshev, V.P.Goranskij, A.M.Cherepashchuk, Sv Astron. Letters 9, 1, 1983; S.A.Gladyshev, V.P.Goranskij, A.M.Cherepashchuk, Sv Astron. Journal V.64, 1037, 1987; A.A.Aslanov, A.M.Cherepashchuk, V.P.Goranskij, V.Yu.Rakhimov, R.C.Vermeulen, AsAp V.270, 200, 1993; V.P.Goranskij, V.F.Esipov, A.M.Cherepashchuk, Rus. Astronomy Reports V.42, 209, 1998.
As: A.V.Zharova with the SAI Crimean Station 60 cm telescope and CCD Apogee Aspen.
c6,c7,s7,s7j,c8,47,VA: V.P.Goranskij with the SAI Crimean Station 60 cm telescope, CCDs SBIG ST-6, ST-7, ST-8, Apogee-47, VersArray and BVRcRjIj filters.
ch: A.M.Cherepashchuk, MNRAS V.194, 761, 1981.
fa: I.M.Kopylov, R.N.Kumajgorodskaya, N.N.Somov, T.A.Somova, S.N.Fabrika, Sv Astron. Journal V.63, 690, 1986.
fe: J.Fukue, R.Nakashima, J.Arimoto, Y.Awano, S.Honda, K.Ishikawa, T.Kato, N.Kawai, K.Matsumoto, M.Okugami, T.Sakaguchi, Y.Tajima, K.Tanabe, K.Tsuda, J.Watanabe, T.Yokoo, PASJ V.49, 93, 1997.
gi: A.B.Giles, A.R.King, R.F.Jameson, M.R.Sherrington, J.H.Hough, J.A.Bayley, E.C.Cunningham, Nature 286, 689, 1980.
ir: T.R.Irsmambetova, Sv Astron. Letters (Pis'ma v A.Zh.) V.23, 341, 1997.
it: V.P.Goranskij, photography with the image tube.
IV: I.Volkov, IBVS No.6022, 2012.
jp: ASCA Compaign (D.Nogami, K.Takagishi, D.Strange, E.Leibowitz, M.Yamauchi, et al.)
ma: B.Margon, H.C.Ford, J.I.Katz, K.B.Kwitter, R.K.Ulrich, R.P.S.Stone, A.Klemola, ApJ V.230, L41, 1979.
ne: S.I.Neizvestnyi, S.A.Pustyl'nik, E.V.Efremov, Pis'ma v AZh V.6, 700, 1980.
or,wi,ks,to,mk: J.C.Kemp, G.D.Henson, D.J.Kraus, L.C.Caroll, I.C.Deardsley, K.Takagishi, J.Jugaku, M.Matsuoka, E.M.Leibowitz, T.Mazeh, H.Mendelson, ApJ V.305, 805, 1986.
Pi,PJ: V.P.Goranskij with the SAI Crimean Station 50 cm Maksutov telescope and CCD MEADE Pictor-416.
SB: Direct images taken with the Japan 8 m Subaru telescope and Fine Object Camera.
sc: N.M.Shakhovskoi, A.N.Sazonov, 1996, Sv Astron. Letters V.22, 517, 1996.
SO: V.P.Goranskij and E.A.Barsukova with the SAO 1 m Zeiss telescope and UBVRcIc photometer based on CCD EEV 42-40.
sz: A.N.Sazonov, Astron. Zirkular No.1531, 13, 1988.
ve: R.C.Vermeulen, P.G.Murdin, E.P.J.van den Heuvel, S.N.Fabrika, B.Wagner, B.Margon, J.B.Hutchings, R.T.Shilizzi, M.H.van Kerkwijk, L.B.van den Hoek, E.Ott, L.P.Angebault, G.K.Miley, S.D'Odorico, N.Borisov, AsAp V.270, 204, 1993.
zc: T.Zwitter, M.Calvani, S.D'Odorico, AsAp V.251, 92, 1991 (correction V = Vz +0.5).
x: Other unclarified sources.