be understood as a scaled-up version of the latter.'
address:
- 'Centro de Radioastronomía y Astrofísica, UNAM, Apdo. Postal 3-72, Morelia, Michoacán, 58089 México'
- 'Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA'
- 'Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile'
- 'Australia Telescope National Facility, P.O. Box 76, Epping NSW 1710 Australia'
- 'Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile'
author:
- 'Luis F. Rodríguez'
- 'James M. Moran and Ramiro Franco-Hernández[^1]'
- Guido Garay
- 'Kate J. Brooks'
- Diego Mardones
title: 'The Collimated Jet Source in IRAS 16547-4247: Time Variation, Possible Precession, and Upper Limits to the Proper Motions Along the Jet Axis'
---

To appear in The Astronomical Journal

Introduction
============

A successful model of low-mass star formation, based on accretion via a circumstellar disk and a collimated outflow in the form of jets (Shu, Adams, & Lizano 1987), has been developed and found to be consistent with the observations. An important question related to star formation is whether or not this model can be scaled up for the case of high-mass protostars or if other physical processes (i.e., stellar merging; Bonnell, Bate, & Zinnecker 1998; Stahler, 