Calibration Sources for CRIRES

Abstract

We report on our efforts to provide high accuracy wavelength calibration to the scientific observations with the Cryogenic High-Resolution IR Echelle Spectrograph (CRIRES), ESO’s new high resolution (R≈100,000) infrared (IR) spectrograph at the VLT. In order to provide reliable and accurate wavelength standards for CRIRES the European Southern Observatory (ESO), in collaboration with the Space Telescope European Co-ordinating Facility (ST-ECF) and the National Institute of Standards and Technology (NIST), embarked on a project to establish Th–Ar wavelength standards in the 950nm to 5000nm operating range of CRIRES. Based on current findings we conclude that Th-Ar hollow cathode lamps hold the promise of becoming a standard source for wavelength calibration for near IR astronomy, providing a high density of sharp well-characterized emission lines with the ease and efficiency of operation of a commercial discharge lamp. In addition, and for use at wavelengths larger than 2200, we have established a gas cell filled with N₂O as a calibration source based on existing data from NIST. Both sources were extensively tested during CRIRES commissioning runs and both are now being used for routine operations of the instrument.