For this example of NPOI data reduction and analysis we use observations of Mizar from 1997. This binary is identified as FKV0497 in the data. We do skip a few steps which would go into too much detail, instead we concentrate on calibration, imaging, and modeling.

This exercise completely skips the reduction steps needed to obtain averaged visibilities. They include reading the raw data and computing visibilities (done by a standalone C program called CONSTRICTOR), editing the 1s incoherent averages and averaging these data for every scan. The latter steps are done with OYSTER, but for this lab it is not useful to have these steps performed by the participants. Rather, we have created an automated script which takes us directly to where we can begin calibrating the data.

Reducing data

So begin with reading an HDS file containing 1s averages of the visibility data.


GeoParms loaded.
GenConfig loaded.
Warning(DAT_FIND): component not found (METROCONFIG)!
Scantable created.
Backgroundtable created.
Background data loaded.
StarTable created; number of entries = 8.
Finished reading catalogs.
Finished reading catalogs.
Number of new diameters added: 6.
Number of new (R-I) values found: 0.
Finished reading catalogs.
Allocated arrays for 33 scans in 3 ob's; MB = 1, MS = 32, MP = 2054
Reference station set.
Data loaded.
Warning(GET_SCANLOG): SCANLOG not found!
Observer log read.
You now have the data; call the automated script to finish the reduction.


At this point let's bring up the main GUI (or widget) which, besides the IDL command line, provides another way of communicating with the software.


In the following exercises, both widgets and command line procedures are going to be used for the data analysis. Plotting, because of the many selections and options, is done most easily through widgets with a fixed functionality. However, at any time, regular IDL commands can be issued, providing a truly interactive and flexible environment.

Note that some images of widgets in this document are clickable for more detailed explanations.