The Use of Absorption Cells as a Wavelength Reference for Precision Radial Velocity Measurements in the Near-Infrared

Considerable interest is now focused on the detection of terrestrial mass planets around M dwarfs, and radial velocity surveys with high-resolution spectrographs in the near-infrared (NIR) are expected to be able to discover such planets. We explore the possibility of using commercially available molecular absorption gas cells as a wavelength reference standard for high-resolution fiber-fed spectrographs in the NIR. We consider the relative merits and disadvantages of using such cells compared with thorium–argon emission lamps and conclude that in the astronomical H band, they are a viable method of simultaneous calibration, yielding an acceptable wavelength calibration error for most applications. Four well-characterized and commercially available standard gas cells of H 13 C 14 N, 12 C 2 H 2 , 12 CO, and 13 CO can together span over 120 nm of the H band, making them suitable for use in astronomical spectrographs. The use of isotopologues of these molecules can increase line densities and wavelength coverage, extending their application to different wavelength regions.