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 H¹³C¹⁴N, ¹²C₂H₂, ¹²CO, and ¹³CO 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.