Spectro-astrometry: The Method, it’s Limitations and Applications Emma Whelan 1 and Paulo Garcia 2,3 1 Dublin Institute for Advanced Studies, School of Cosmic Physics ewhelan@cp.dias.ie 2 Departamento de Engenharia F´ ısica, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal 3 Centro de Astrof´ ısica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal pgarica@astro.up.pt Abstract Intermediate resolution spectroscopic observations provide a window into the immediate environment of young stars. In particular such studies have yielded much new information regarding outflow activity and binarity. Using spec- troscopy one can investigate the kinematics and excitation conditions of jets close to where they are launched and resolve close binaries. The primary con- straint to the use of spectroscopy in this manner is the maximum spatial resolution achievable. Observers are all the time aiming to improve angu- lar resolution and overcome the limiting effects of the Earth’s atmosphere. This is where the technique of spectro-astrometry comes to the fore. The spectro-astrometric technique, which allows the user to recover sub-seeing spatial information from a simple spectrum has been applied to many inter- esting problems. For example spectro-astrometry has been used to discover that brown dwarfs can drive outflows. In this review of spectro-astrometry we shall discuss the technique beginning with a revision of angular resolution and astrometry. The limitations of the technique are described and the uses to which it has been put to date are extensively discussed. 1 The Spectro-astrometric Technique The modern astronomer’s understanding of a wide range of astronomical phe- nomena is greatly limited by the need for better angular resolution. For ex- ample, we have not yet achieved the resolution required to obtain a compre- hensive picture of how jets from young stars (the topic at the heart of this series of lectures) are launched. The complicated techniques of adaptive op- tics and interferometry (thoroughly described in this book) are designed to,