Star Classification Possibilities with the Gaia Spectrophotometers. II. A Method for Empirical Decontamination of the BP/RP Spectra

Abstract

Abstract The contamination in the Gaia BP and RP spectra, caused by the LSF smearing, is a serious obstacle for the classification of stars since the contamination values at different wavelengths depend on temperatures, gravities, metallicities and interstellar reddenings of stars, and these parameters are unknown before the classification. This makes impossible to apply traditional methods for photometric classification of stars based on color indices or interstellar reddening-free Q-parameters. For determining contamination for the stars of ‘normal’ spectral sequence we propose the method of ‘color equations’, well known in stellar photometry. The equations connecting the decontamination correction at a chosen wavelength with the observed ‘color indices’ are derived. These equations make possible to determine decontamination corrections for unreddened stars with an accuracy of 0.01-0.02 mag in the wavelength range of 400-1000 nm. The equations are different for M-type stars which can be separated from stars of earlier spectral classes using the contaminated RP spectra and treated separately. The equations are valid not only for unreddened stars but also for stars affected by interstellar extinction up to AV = 3 mag. At shorter wavelengths (350-400 nm) the contamination is much larger and can be determined with lower accuracy.