Using the VLBA, we have observed H2O maser emission in the pre-planetary
nebula IRAS 19134+2131(I19134), in which the H2O maser spectrum has two groups
of emission features separated in radial velocity by ~100 km/s. We also
obtained optical images of I19134 with the HST to locate the bipolar reflection
nebula in this source for the first time. The spatio-kinematical structure of
the H2O masers indicates the existence of a fast, collimated (precessing) flow
having a projected extent of ~140 mas and an expansion rate of ~1.9 mas/yr on
the sky plane, which gives a dynamical age of only ~40 yr. The two detected
optical lobes are also separated by ~150 mas in almost the same direction as
that of the collimated flow. The good agreement between the extent and
orientation of the H2O maser outflow and optical lobes suggests that the lobes
have been recently formed along the collimated fast flow. The positions of all
of the detected maser features have been measured with respect to the reference
source J1925+2106 over one year. Therefore we analyzed maser feature motions
that consist of the combination of an annual parallax, a secular motion
following Galactic rotation, and the intrinsic motions within the flow. We
obtain an annual-parallax distance to I19134 of D~8 kpc kpc and estimate its
location in the Galaxy to be (R, theta, z)=(7.4 kpc, 62 deg, 0.65 kpc). From
the mean motion of the blue-shifted and red-shifted clusters of maser features,
we estimate the 3-D secular motion of I19134 to be (V_{R}, V_{theta},
V_{z})=(3, 125, 8) [km/s]. From the height from the Galactic plane, z, and the
velocity component perpendicular to the Galactic plane, V_{z}, we estimate a
rough upper limit of ~9 M_{sun} to the stellar mass of I19134's progenitor.Comment: 17 pages, 5 figures, to appear in the Astrophysical Journal, October
20 issu
