To save space, the FITS file and the plain text file can be compressed in gzip format and iSpec can automatically compress/decompress. Wavelength should be in nanometers, if it is not the case, it can still be loaded into iSpec and transformed using the "Apply mathematical operation" option (e.g. Three columns should exists: wavelength, flux and error (although in case the error is unknown, it can be set all to zero). ISpec can also read plain text files with tab character as column delimiter.
In both cases, Angstrom is assumed as unit and transformed to nanometers internally, unless the CUNIT value is set on the header indicating otherwise. FITS files containing a table in the primary extension where columns are wavelength, fluxes and, optionally, errors.1-D FITS file with CDELT/ CRVAL values in the header and fluxes in the primary extension.mand input/spectra/examples/NARVAL_Sun_ Spectra file formats ISpec can also be executed from command line indicating directly the spectra to be opened. This will plot two discontinuous lines above and below the spectrum representing the flux +/- the errors. The flux errors can be plotted by activating "Spectra - Show errors in plot". In case the spectrum has been modified and not saved, iSpec will ask for confirmation before closing it. To change the active spectra, the user has to select a different one through the menu "Spectra - Name of the spectrum" or directly closing the active one through "Spectra - Close spectrum". Operations such as radial velocity determination are executed only on the active spectrum. At every moment, only one spectrum is active and its marked with a "" symbol in the legend box. ISpec can open multiple spectra files simultaneously through the menu "File - Open spectra". The visual interface can be launched by double clicking "mand" or executing in a terminal located in iSpec's directory. In this section ('Usage' section), we will learn how to use the visual interface and some fundamental aspects of iSpec. Scripting give access to all the functionalities and ensures reproducibility, which is a very important feature for science.
Once the user is familiarized with iSpec, it is recommended to work mainly with Python scripts. The visual interface is convenient to learn the fundamental aspects of iSpec, to test the result of certain operations and for educational purposes. Nevertheless, there are options and functionalities that can only be accessed via Python. ISpec provides a visual interface from where the user can interact with the spectra and use different useful functionalities.
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