Flux calibration of medium-resolution spectra from 300 nm to 2500 nm: Model reference spectra and telluric correction

Institute for Astronomy and Astrophysics, Kepler Center for Astro and Particle Physics, Eberhard Karls University, Sand 1, 72076Tu¨bingen, Germany (e-mail:rauch@astro.uni-tuebingen.de)Received 10 March 2014 / Accepted 7 April 2014ABSTRACTContext.While the near-infrared wavelength regime is becoming moreand more important for astrophysics there is a marked lackof spectrophotometric standard star data that would allow the flux calibration of such data. Furthermore, flux calibrati ng medium- tohigh-resolution e´chelle spectroscopy data is challenging even in the optical wavelength range, because the available flux standard dataare often too coarsely sampled.Aims.We will provide standard star reference data that allow users to derive response curves from 300nm to 2500nm for spec-troscopic data of medium to high resolution, including those taken with e´chelle spectrographs. In addition we describe a method tocorrect for moderate telluric absorption without the need of observing telluric standard stars.Methods.As reference data for the flux standard stars we use theoretic al spectra derived from stellar model atmospheres. We verifythat they provide an appropriate description of the observed standard star spectra by checking for residuals in line cores and lineoverlap regions in the ratios of observed (X-shooter) spectra to model spectra. The finally selected model spectra are th en correctedfor remaining mismatches and photometrically calibrated using independent observations. The correction of telluric absorption isperformed with the help of telluric model spectra.Results.We provide new, finely sampled reference spectra without tel luric absorption for six southern flux standard stars that al lowthe users to flux calibrate their data from 300nm to 2500nm, an d a method to correct for telluric absorption using atmosphericmodels.Key words. standards – Techniques: spectroscopic