Monitoring of long term behaviour of OH masers in semiregular variables: R Crt, W Hya and RT VirS. Etoka, L. Błaszkiewicz, M. Szymczak and A. M. Le SquerenA&A, 378 2 (2001) 522-538DOI: https://doi.org/10.1051/0004-6361:20011184
