The first observations of outflows in the infrared date back to the 1980s, with the pioneering^ 2.12|m works (e.g. [2, 54]), where observations were done with single channel detectors coupled with CVF filters. Since then, the progress in IR observations has been enormous, thanks to the development of sensitive IR arrays with progressively larger dimensions and to the higher

B. Nisini: IR Spectroscopy of Jets, Lect. Notes Phys. 742, 79-104 (2008)

DOI 10.1007/978-3-540-68032-1.4 (c) Springer-Verlag Berlin Heidelberg 2008

spatial resolution now provided by the 8-m class telescopes with Adaptive Optics (AO) system. Not only have ground-based NIR observations seen a boost, thanks to technology development, but in the last decade, the ISO and Spitzer missions have also shown the potential of mid-and far-IR spec-troscopic observations, opening a new window for the study of warm gas at low excitation. The new frontier in high angular resolution IR observations is now represented by the IR interferometry, and projects like the VLTI and CHARA are expected to make a new revolution in our understanding of jet physics.

The fast improved quality of the data and the access to a large wavelength coverage have also fostered the development of new and more sophisticated tools for data interpretation. As a consequence, during the last years a large variety of models for the interpretations of IR observations of outflows have been developed, which run from line predictions in shocks to synthetic images from disk-wind models and numerical simulations.

In this contribution, after an introduction on the advantages and complementarity given by observations of jets in the IR with respect to the optical and on the limitations imposed by the atmosphere and technology, I will review the properties of the main emission lines at near- and mid-IR wavelengths and how they can be used to infer the main jet physical parameters. Finally,

1 will present some recent results obtained by HAR observations in jets from embedded young sources. NIR AO-assisted observations in T Tauri jets will be reviewed in the Dougados contribution to this book. Other useful reviews on IR observations of jets and outflows can be found in [3] and [45].

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