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==> This proposal requests an upgrade from Priority 3 for DENGELS.WASSER
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I propose to observe with a Fabry-Perot line scan one of the key transitions
of the H2O molecule in the long-period variable OH/IR star OH 39.7+1.5, which
is passing through its maximum in 1997 February. This key transition is
connected to one of the 6(16) and 5(23) levels, which give rise to the
prominent and well observed 22 GHz (1.3 cm) maser line. This observation is an
upgrade of a current Grade 3 observation allocated for the proposal WASSER.
This proposal was aimed to study the pump mechanism of the 22 GHz H2O maser.
Several transitions were planned to be measured in 4 prototype stars,
and some of them during minimum and maximum of their light cycle. 21600s Grade
6 and 14400s Grade 3 time was allocated. The changes in LWS04 performance
and its late release reduced this program to a rather limited core.
The strong H2O maser Mira variable IRC+10011 will be observed at a random
phase, and the weak H2O maser star o Cet (Mira) during maximum. I propose
to add OH 39.7+1.5 to this list, because this stars is the only OH/IR star
in this proposal (and the only one in similar proposals), and therefore
probes another (much higher) mass loss regime, because we have a
continuous 22 GHz H2o maser lightcurve of this star since 1990 including
four VLA maps, and because the star is passing through its maximum during
next year.
These observations and similar ones from other proposals will be used in
connection with an ongoing 22 GHz monitoring program to study the role of the
pump mechanism.