Astrophys. J., 771, 47 (2013/July-1)
Exploration of a relic circumstellar envelope in the "Water fountain" source IRAS 18286-0959.
IMAI H., NAKASHIMA J.-I., YUNG B.H.K., DEGUCHI S., KWOK S. and DIAMOND P.J.
Abstract (from CDS):
The water fountain source IRAS 18286-0959 (I18286) was reported as an object exhibiting highly collimated, double-helix stellar jets traced by the H2 O maser emission. Using the European VLBI Network, we measured the absolute coordinates of the 1612 MHz OH maser emission in I18286, which is very likely associated with a relic of a circumstellar envelope (CSE) developed in the asymptotic giant branch stage of the central star. The location of the OH maser is near the center of the H2 O maser feature cluster, where one of the originating points of the two jets is located. We also mapped 22.2 GHz H2 O maser emission in this object using the Very Long Baseline Array in the seasons of 2006-2007 as well as 2008-2009. In the first three epochs in 2006-2007, we detected at least 90 maser features per epoch. In six epochs in 2008-2009, when the observation data had already been published and analyzed to identify the double-helix jets, we newly identified 14 proper motions of H2 O maser features which could not be measured in the previous analysis due to their short lifetimes. In this paper, together with the OH maser emission, we focus on "outlier" H2 O maser features, which exhibit slow expansion velocities (Vexp ≲ 30 km/s) and are likely associated with either the relic CSE or an equatorial flow of I18286. They were marginally distinguishable from the maser features associated with the jets in I18286.
masers - stars: AGB and post-AGB - stars: individual: IRAS 18286-0959 - stars: mass-loss - stars: winds, outflows
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