22 GHz Observations of Southern H2O Sources

Abstract

The discovery of three new H20 sources associated with HII regions is reported. Observations of other southern H20 sources show, in several instances, considerable intensity changes over a 20-month interval.

Galactic Plane H2O Masers: A Southern Survey

“…Since 1973 June (Caswell et al 1974) this has remained one of the strongest H 2 0 sources; the high-velocity features detected in 1975 May were not detected in 1976 August, but the overall appearance (Fig. 1) remains similar though weaker by a factor of '" 2.…”

“…The position quoted is the discovery position where there is an OH source (Caswell and Haynes 1975 ; K + 76, K + 77) near the position of one of the remarks of Genzel and Downes (1977b), it is not clear why this should be expected from their model.…”

“…This source was discovered in 1975 November by K+ 76 and K+ 77 near the position of an OH maser (Caswell and Haynes 1975); our 1976 profile (Fig. 2) shows the peak intensity now at the position of a secondary feature of the K + 77 spectrum, with intensity approximately three times greater. '…”

“…The discovery observation (1975 December) showed a peak of 70 Jy which had fallen to 30 Jy by 1977 May (our next observation, during which a position was measured). The associated OH source has some of the characteristics of a late type OH/IR star (Caswell and Haynes 1975 (not present in 1976) was the strongest feature (see Fig. 3).…”

“…Since 1973 June (Caswell et al 1974) this has remained one Galactic Plane H2 0 Masers 153 a further cause for surprise. Application of Occam's razor suggests an alternative explanation which appeals to us but which we have not yet had the opportunity to verify.…”