The spatio-kinematical structure and distance of the pre-planetary nebula IRAS 19134+2131

TL;DR

This study uses VLBA and HST observations to analyze the structure, motion, and distance of the pre-planetary nebula IRAS 19134+2131, revealing a recent collimated outflow and estimating its galactic position and stellar mass.

Contribution

First detailed VLBA and HST analysis of IRAS 19134+2131's maser and optical structures, providing new insights into its outflow dynamics and galactic location.

Findings

Detected a fast, collimated, precessing flow with a ~40-year dynamical age.

Measured an annual-parallax distance of approximately 8 kpc.

Estimated the progenitor star's mass to be less than about 9 solar masses.

Abstract

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.