In an interferometer system and a method for its operation, the interferometer system includes an interferometer having an interferometer light source whose emitted radiation is able to be split into a measuring arm and a reference arm, an object to be measured being disposed in the measuring arm, and the interferometer delivering interferometer signals as a function of the position of the object to be measured. In addition, a detecting device is provided for detecting fluctuations in the refractive index of the air in the measuring arm and/or reference arm. The detecting device includes a spectrometer unit; the spectrometer unit has at least one spectrometer light source, as well as at least one spectrometer detector unit. The bundles of rays emitted by the spectrometer light source are superimposed on the bundles of rays from the interferometer light source, the spectrometer light source emitting radiation having a wavelength which lies in the range of an absorption line of at least one specific air component. The spectrometer detector unit is used to generate spectrometer signals which characterize the absorption of the air component in terms of the spectrometer light-source wavelength in the measuring arm and/or reference arm.