About OYSTER

$\cal OYST\!ER\,$is the original interactive data reduction package developed for the Navy Precision Optical Interferometer at Lowell (NPOI). $\cal OYST\!ER\,$is an endeavor to combine all aspects of data reduction, modeling, astrometry, and imaging, including a stellar database, with an interactive data language in one package. Procedures are often shared. It also tries to maximize ease of use by providing both command line procedures and widget routines.

• HDS data base access: A full set of functions to access NPOI data files written in the Hierarchical Data System format (developed by Starlink). Individual objects can be accessed directly.
• Plotting and editing: General plotting widgets, with interactive display options and editing routines. Flagtables are implemented for bookkeeping.
• Astrometry: Multi-color dispersion corrections, metrology calibration, astrometric functions including the Naval Observatory Vector Astrometry Subroutines, epoch conversions, and polar motion data. Solution for baseline and star coordinates.
• Calibration: General multi-dimensional visibility amplitude and phase calibration capability for several types of dependencies.
• Global modeling: Use of a hierarchical stellar systems format which enables fitting physical parameters directly to any combination of data from interferometry, spectroscopy, photometry, and astrometry.
• Stellar spectra and limb darkening: atmospheric models which are used in bandwidth smearing computations and modeling. Display of stellar spectra and line identifications.
• Stellar data base: procedures for star catalog access. Storage of data in a table, and procedures for estimation of physical parameters of stars, like diameters, masses, orbital elements.
• Planning of observations: A set of procedures for computing visibility and simulating data for scheduling. The stellar data base serves to aid in the selection of calibrator stars.

$\cal OYST\!ER\,$was created when three collections of scripts written first in PV-WAVE Command Language (PV-WAVE is a trademark of Rogue Wave Software) and then also in the Interactive Data Language (IDL is a trademark of Exelis Visual Information Solutions) were merged into one package for the purpose of providing a comprehensive data analysis package. The PV-WAVE version of $\cal OYST\!ER\,$is however no longer supported, while support for GDL (Gnu Data Language) has been added with version 8 of $\cal OYST\!ER\,$(no GUI support).

The three original collections, CHAMELEON which reduces a single night of NPOI data, AMOEBA which fits models to the calibrated visibility data of several nights, and STARBASE which implements a stellar data base and provides catalog access, are described in this User's Guide in separate parts. Also introduced are two new collections of scripts, COBRA, which provides functions for the interactive analysis of raw interferometry data (NPOI only), and PEARL, which images interferometry data.

As of 2014, $\cal OYST\!ER\,$has evolved into a package also supporting the reduction and analysis of data from interferometers other than NPOI. This includes the GUI front-ends MyMidiGui and MyAmberGui to the MIA+EWS (http://www.strw.leidenuniv.nl/$\sim$nevec/MIDI/index.html) and amdlib (http://www.jmmc.fr/data_processing_amber.htm) data reduction softwares for MIDI and AMBER at VLTI, respectively. Also, observation planning and advanced data analysis is available in $\cal OYST\!ER\,$. Stand-alone reduction of data from other interferometers is not planned to be included in $\cal OYST\!ER\,$since this involves obviously very instrument specific tasks.

Data of other interferometers can be read and modeled by $\cal OYST\!ER\,$ if they are stored using the OIFITS format (http://www.mrao.cam.ac.uk/research/OAS/oi_data/oifits.html).