1. R. Bachiller, Ann. Rev. Astron. Astrophys. 34, 111 (1998).
2. L. I. Matveenko, Pis’ma Astron. Zh. 7, 100 (1981) [Sov. Astron. Lett. 7, 54 (1981)].
3. L. I. Matveenko, P. D. Diamond, and D. A. Graham, Pis’ma Astron. Zh. 24, 723 (1998) [Astron. Lett. 24, 623 (1998)].
4. L. I. Matveenko, P. D. Diamond, and D. A. Graham, Astron. Rev. 80, 592 (2000).
5. L. I. Matveenko, P. D. Diamond, and D. A. Graham, IAU Symp. 206: Cosmic Masers: from Protostars to Blackholes, Ed. by V. Migenes and M. J. Reid (2002), p. 96.