Rapidly evolving episodic outflow in IRAS 18113−2503: clues to the ejection mechanism of the fastest water fountain. (21st September 2018)

• Record Type: Journal Article
• Authors: Orosz, G; Gómez, J F; Imai, H; Tafoya, D; Torrelles, J M; Burns, R A; Frau, P; Guerrero, M A; Miranda, L F; Perez-Torres, M A; Ramos-Larios, G; Rizzo, J R; Suárez, O; Uscanga, L
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 482:Number 1(2019)
• Page Start: L40
• Page End: L45
• Publication Date: 2018-09-21
• Subjects: masers -- astrometry -- stars: AGB and post-AGB -- binaries: general -- stars: individual (IRAS 18113–2503) -- stars: jets; Astronomy -- Research -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnrasl/sly177
• Languages: English
• ISSNs: 1745-3933

Abstract

ABSTRACT: Water fountains are evolved stars showing early stages of collimated mass-loss during transition from the asymptotic giant branch, providing valuable insight into the formation of asymmetric planetary nebulae. We report the results of multi-epoch VLBI observations, which determine the spatial and three-dimensional kinematic structure of H2 O masers associated with the water fountain IRAS 18113−2503. The masers trace three pairs of high-velocity (∼150–300 km s −1 ) bipolar bow shocks on a scale of 0${^{\prime\prime}_{.}}$ 18 (∼2000 au). The expansion velocities of the bow shocks exhibit an exponential decrease as a function of distance from the central star, which can be explained by an episodic, jet-driven outflow decelerating due to drag forces in a circumstellar envelope. Using our model, we estimate an initial ejection velocity ∼840 km s −1, a period for the ejections ∼10 yr, with the youngest being ∼12 yr old, and an average envelope density within the H2 O maser region $n_{\text{H}_2}{\approx }10^{6}$ cm −3 . We hypothesize that IRAS 18113−2503 hosts a binary central star with a separation of ∼10 au, revealing novel clues about the launching mechanisms of high-velocity collimated outflows in water fountains.