Quantifying Chromospheric Activity by Using the Spectral Subtraction Technique: iSTARMOD code

Here we describe the Python code iSTARMOD implemented to apply the spectral subtraction technique and quantify the chromospheric activity of cool stars. This method is based in the subtraction of a synthesized stellar spectrum constructed using artificially rotationally broadened, radial-velocity shifted, and weighted spectrum of an inactive star chosen to match the spectral type and luminosity class of the active star under consideration. This code can be applied to both single stars and binaries, taking into account the contribution of each component to the observed spectrum. Reference spectra are typically those of stars observed with the same instrumental configuration as the star in question, but it is also possible to use synthetic spectra generated by models. It measures excess chromospheric emission in late-type stars across several activity indicators, such as Hα and the other Balmer lines in the visible, He I D3 and Na I D1, D2, Ca II H and K, and Ca II infrared triplet, as well as the Paschen series and He I λ10830 lines in the near-infrared. The iSTARMOD code is accompanied with a series of calibrations of χ-functions, to transform the excess emission equivalent widths measured through iSTARMOD into absolute surface fluxes. The code can be used from the console or through a graphical unit interface (GUI) and is available in GitHub: https://github.com/flabarga/iSTARMOD