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The Spectrum of Th-Ar Hollow-Cathode Lamps in the 900 nm to 4500 nm Region: Establishing Wavelength Standards for the Calibration of VLT Spectrographs



F Kerber, Gillian Nave, Craig J. Sansonetti, P Bristow, A Rosa, H-U Kaufl, Michael R. Rosa


The European Southern Observatory (ESO), the Space Telescope European Co-ordinating Facility (ST-ECF), and the National Institute of Standards and Technology (NIST) are collaborating to study Th-Ar hollow cathode lamps as used for the calibration of VLT (Very Large Telescope) spectrographs. Th-Ar hollow cathode lamps provide a rich spectrum in the UV-visible region and have been used in astronomy for a long time. We report new measurements using the 2-m UV/visible/IR Fourier transform spectrometer (FTS) at NIST that establish more than 2000 lines as wavelength standards in the range 900 nm to 4500 nm. This line list is used as input for a physical model that provides the wavelength calibration for the Cryogenic High-Resolution IR Echelle Spectrometer (CRIRES), ESO's new high resolution (R 100,000) IR spectrograph at the VLT. We also present first calibration results from laboratory testing of CRIRES. The newly established wavelength standards will also be available for use by X-shooter and other spectrographs in the future. Measurements of the variation of the spectrum of Th-Ar lamps as a function of operating current allow us to optimise the spectral output in terms of relative intensity and line density for operation on the telescope. Since Th and Ar line intensities show a different response with respect to operating current, such measurements can be used as a diagnostic tool for distinguishing the gas and metal lines. Our findings show that ThAr lamps hold the promise of becoming a standard source for wavelength calibration in near IR astronomy.
Proceedings Title
Ground-based and Airborne Instrumentation for Astronomy
Conference Dates
May 1, 2006
Conference Location
Conference Title
SPIE Proceedings


CRIRES, fourier transform spectroscopy, near infrared, Th/Ar hollow cathode lamp, wavelength calibration


Kerber, F. , Nave, G. , Sansonetti, C. , Bristow, P. , Rosa, A. , Kaufl, H. and Rosa, M. (2006), The Spectrum of Th-Ar Hollow-Cathode Lamps in the 900 nm to 4500 nm Region: Establishing Wavelength Standards for the Calibration of VLT Spectrographs, Ground-based and Airborne Instrumentation for Astronomy, Undefined (Accessed September 27, 2023)
Created April 30, 2006, Updated October 12, 2021