Reliable elimination of telluric lines from stellar spectra

We demonstrate that the powerful disentangling technique used to separate the individual spectra of binary components and telluric lines can also be used to remove telluric lines from the spectrum of a single star by treating the telluric spectrum as a second star. We tested that on the spectra of alpha Boo (= Arcturus) secured with a Reticon detector in the coude focus of the Ondrejov 2-m telescope. We demonstrate that the method works well and is invaluable especially for the spectra of red stars which are heavily blended with the telluric lines. The disadvantage of the method is that one needs a number of spectra of the star in question, secured at different months of the year. The advantage is that one obtains the final disentangled stellar spectrum with a high S/N ratio.