Using the Very Long Baseline Array and the European VLBI Network , we have observed 22.2 GHz H _ { 2 } O and 1612 MHz OH masers in the water fountain source IRAS 18460 - 0151 .
The H _ { 2 } O maser spectrum has a very wide line-of-sight velocity range ( \approx 310 km s ^ { -1 } ) and consists of three groups of emission features at the blue-shifted ( -68 km s ^ { -1 } \lesssim V _ { \mbox { \scriptsize LSR } } \lesssim - 17 km s ^ { -1 } ) and red-shifted ( V _ { \mbox { \scriptsize LSR } } \simeq 240 km s ^ { -1 } ) edges as well as around the systemic velocity ( 112 km s ^ { -1 } \lesssim V _ { \mbox { \scriptsize LSR } } \lesssim 133 km s ^ { -1 } ) .
The first two H _ { 2 } O spectral components exhibit a highly-collimated high-velocity bipolar jet on the sky , with an angular separation of \approx 120 milliarcseconds ( mas ) ( 240 AU in linear length ) and a three-dimensional flow velocity of \approx 160 km s ^ { -1 } .
The flow dynamical age is estimated to be only \approx 6 yr ( at the time of the observation epochs of 2006–2007 ) .
Interestingly , the systemic velocity component clearly exhibits a spherically-expanding outflow with a radius of \approx 36 AU and a flow velocity of \approx 9 km s ^ { -1 } .
On the other hand , the OH maser spectrum shows double peaks with a velocity separation of \approx 25 km s ^ { -1 } ( V _ { \mbox { \scriptsize LSR } } = 111–116 and 138–141 km s ^ { -1 } ) , as typically seen in circumstellar envelopes of OH/IR stars .
The angular offset between the velocity-integrated brightness peaks of the two high-velocity H _ { 2 } O components is \approx 25 mas ( 50 AU ) .
The offset direction and the alignment of the red-shifted maser spots are roughly perpendicular to the axis of the H _ { 2 } O maser flow .
High-accuracy astrometry for the H _ { 2 } O and OH masers demonstrates that the collimated fast jet and the slowly expanding outflow originate from a single or multiple sources which are located within 15 mas ( 30 AU ) .
On the other hand , the estimated systemic velocity of the collimated jet ( V _ { sys } \approx 87–113 km s ^ { -1 } ) has a large uncertainty .
This makes it difficult to provide strong constraints on models of the central stellar system of IRAS 18460 - 0151 .