The purpose of these pages is to accompany computer lab exercises for working with interferometric data. The software used is the OYSTER collection of IDL scripts, which reduce, calibrate, and model NPOI data.

The idea is to use the software to follow the steps outlined in these pages, and to experiment further in order to learn about real interferometric data and its analysis.

It is the intention of these classes to learn about principle aspects of interferometric data reduction, not so much about a specific software. Each interferometer, be it SUSI, IOTA, PTI, CHARA, or GI2T, have their own packages and even strategies or pecularities, which are not subject to this course. But there are common features, and those will hopefully be demonstrated in the following.


The author of this lab session and OYSTER asks you to keep in mind that the software is not guarenteed and that the instructions in this document may (and are probably) not complete. He would therefore appreciate any comments sent to

Note for Windows Users

OYSTER has not been released for Windows. However, you should be able to perform the calibration, imaging, and modeling exercises with this version since they don't require access to the external library. It is important not to use the get_data procedure; use restore,'1997-05-01.xdr' instead! This restores the file 1997-05-01.cha, which means that you do not use the reduce command, but begin imaging and modeling with this already calibrated data set. If you want to re-calibrate it, remove the existing calibration first (using Undo|Reset for each of the data types VisSq, TripleAmp, and TriplePhase).

You can copy the three OYSTER installation directories (oyster, catalogs, atmospheres) to the hard disk, or run the software directly from the CD-ROM.

When running the IDL graphical user interface (created when double-clicking the IDL icon on the desktop after installing IDL), set the working directory to c:\oyster\lab\data and the startup file to c:\oyster\ Modify full paths as needed. These preferences can be found under File|Preferences. Then restart IDL and it should be running OYSTER after startup is complete.