One-dimensional (1-D) microlens parallaxes can be combined with heliocentric lens-source relative proper motion measurements to derive the lens mass and distance, as suggested by Ghosh et al. (2004). Here I present the first mathematical anlysis of this procedure, which I show can be represented as a quadratic equation. Hence, it is formally subject to a two-fold degeneracy. I show that this degeneracy can be broken in many cases using the relatively crude 2-D parallax information that is often available for microlensing events. I also develop an explicit formula for the region of parameter space where it is more difficult to break this degeneracy. Although no mass/distance measurements have yet been made using this technique, it is likely to become quite common over the next decade.

Abstract
1. INTRODUCTION
2. QUADRATIC FORM
    2.1. Limit of 4AC≪1
    2.2. General Case
3. ERROR ANALYSIS
4. INFORMATION FROM DIRECT IMAGING
5. CONCLUSION
REFERENCES

• ANDREW GOULD(Department of Astronomy, Ohio State University) CORRESPONDING AUTHOR