1. Heckman T.M., Milley G.K., van Breugel, Wil J.B., Butcher H.R. 1981, Astrophys. J., 247, 403.
2. Pelat D., Alloin D., 1982, Astron. Astrophys. 105, 335 (PA paper)
3. Pronik V.I. 1987, Izvest.Krim.Astrofiz.obs., 58, 104.
4. Pronik V.I., Balinskaja I.C. 1983, Astrophys., 19, 17.
5. Schulz H. 1987, Astron. Astrophys., 178, 715.