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
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
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
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
- 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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