THE SPATIOKINEMATICAL STRUCTURE OF H{sub 2}O AND OH MASERS IN THE ''WATER FOUNTAIN'' SOURCE IRAS 18460-0151
- Department of Physics and Astronomy, Graduate School of Science and Engineering, Kagoshima University, 1-21-35 Korimoto, Kagoshima 890-0065 (Japan)
- Nobeyama Radio Observatory, National Astronomical Observatory of Japan, Minamimaki, Minamisaku, Nagano 384-1305 (Japan)
- Department of Physics, University of Hong Kong, Pokfulam Road, Hong Kong (Hong Kong)
Using the Very Long Baseline Array and the European Very Long Baseline Interferometry Network, we have observed 22.2 GHz H{sub 2}O and 1612 MHz OH masers in the water fountain source IRAS 18460-0151. The H{sub 2}O maser spectrum has a very wide line-of-sight velocity range ( Almost-Equal-To 310 km s{sup -1}) and consists of three groups of emission features at the blueshifted (-68 km s{sup -1}{approx}< V{sub LSR} {approx}< -17 km s{sup -1}) and redshifted (V{sub LSR} {approx_equal} 240 km s{sup -1}) edges as well as around the systemic velocity (112 km s{sup -1} {approx}< V{sub LSR} {approx}< 133 km s{sup -1}). The first two H{sub 2}O spectral components exhibit a highly collimated high-velocity bipolar jet on the sky, with an angular separation of Almost-Equal-To 120 milliarcsec (mas) (240 AU in linear length) and a three-dimensional flow velocity of Almost-Equal-To 160 km s{sup -1}. The flow dynamical age is estimated to be only Almost-Equal-To 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 Almost-Equal-To 36 AU and a flow velocity of Almost-Equal-To 9 km s{sup -1}. On the other hand, the OH maser spectrum shows double peaks with a velocity separation of Almost-Equal-To 25 km s{sup -1} (V{sub LSR} = 111-116 and 138-141 km s{sup -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{sub 2}O components is Almost-Equal-To 25 mas (50 AU). The offset direction and the alignment of the redshifted maser spots are roughly perpendicular to the axis of the H{sub 2}O maser flow. High-accuracy astrometry for the H{sub 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{sub sys} Almost-Equal-To 87-113 km s{sup -1}) has a large uncertainty. This makes it difficult to provide strong constraints on models of the central stellar system of IRAS 18460-0151.
- OSTI ID:
- 22130952
- Journal Information:
- Astrophysical Journal, Vol. 773, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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