H2O MASER EMISSION FROM IRREGULAR VARIABLES

We have performed a search for the 22 GHz water maser line among 72 op tically identified irregular and semiregular red variables. New detect ions were made of five stars, while only four of nine objects previous ly known as maser sources were redetected. The probability for the det ection of H2O maser emission increases with V light amplitude, and wit h H - K and K - [12] colours just as in regular Mira and semiregular v ariables of SRa- and SRb-types. The detection rate of water masers is about 25% for nearby Lb objects(D < 400 pc) in the sample, comparable to that observed in the SRa and SRb stars. No masers were detected in objects with mass loss rates less than or equal to 4 10(-8) M.yr(-1). Maser luminosities are 10(41) - 10(43) photons s(-1) similar to that o f the bluest Miras and typical SRa and SRb stars showing water maser e mission. A comparison of our data on irregular stars with those previo usly obtained on SRa and SRb variables suggests that most radio and in frared properties are indistinguishable among both classes of objects.