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Previous studies have shown that ThNe lamps are very suitable for the precise measurement of wavelength variations. A critical issue for all hollow cathode lamps (HCLs) is the current at which the lamp is operated—a low value has the advantage that the lifetime of the lamp is longer whereas the number of useful lines is lower. We investigate the number of suitable spectral lines depending on the current used and the obtained spectra of a ThNe HCL coupled by a fiber to the Tautenburg Echelle spectrograph in a setting that is typical for many high‐resolution spectrographs. Operating currents were chosen in the range specified by the manufacturer. We varied the exposure time to identify the saturation level and the effects of noise. A few thousand Th lines were identified automatically in the wavelength range considered. We noticed a scatter of several hundred m s −1  of Th lines when varying the settings but did not detect any systematic trends. The scatter in wavelength residuals of Th lines, however, indicates that a precise control of the operating current can be necessary. An estimation of the calibration precision of individual lines indicates that a combination of strong Th lines allows one to reach a level of 1 ms −1 . Although a high operating current reduces the lifetime of the lamp and accelerates its aging, it guarantees the highest precision because of the numerous Th lines that become strong compared to the Ne lines. Then, the noise, saturation, and wavelength residuals of the lines can be identified, and the pollution due to saturated Ne lines can be minimized by adjusting the exposure time. Our results indicate that ThNe lamps can be better suited than ThAr lamps for all kinds of studies that involve precise measurement of radial velocity variations, for example, studies on late‐type stars, brown dwarfs, objects that suffer from strong extinction, or high‐red‐shift galaxies.

On the optimum operating conditions of ThNe calibration lamps for measurements of radial velocity variations