OYSTER

About OYSTER

OYSTER is a 50,000+ lines of code project to provide a comprehensive system for displaying, editing, calibrating, and modeling interferometry data. It has been developed by Dr. Christian Hummel over several years at the US Naval Observatory (USNO) and the European Southern Observatory (ESO). IDL (a trademark of Exelis Visual Information Solutions) was chosen as the programming environment because it provides interactive data manipulation and extensive plotting and visualization tools. Coding and debugging are very fast in this environment.

The name OYSTER was derived from OISDR (Optical Interferometry Script Data Reduction). The Navy Precision Optical Interferometer developers believe in real world naming of software.

Modeling interferometric data (AMOEBA) is based on a hierarchical model prescription including analytical models for simple components, and includes external public packages for rotating stars and interacting binaries. Stellar data and their relations as well as stellar spectra are computed and made accessible via scripts (STARBASE). Experimental support for polychromatic imaging based on a multi-wavelength CLEAN algorithm (PEARL) is included.

OYSTER is also used to reduce and calibrate data of the Navy Precision Optical Interferometer (NPOI) operated by USNO, NRL (Naval Research Laboratory) and Lowell Observatory. It offers an automatic pipeline as well for these data (CHAMELEON).

OYSTER is an endeavor to integrate all tasks related to planning and analysing interferometric observations in one package. It also tries to maximize ease of use by providing both command line procedures and GUIs. A 100-page manual is provided. Users can also find instructions on how to build their own library of procedures which take the place of and modify the implemented procedures by compilation at runtime.

Available features of OYSTER include:

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. Global astrometry using sparse matrix technology.
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.
Imaging: provides tools for imaging composite spectrum binaries.
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.

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