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

Abstract

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 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 near-infrared. We consider the relative merits and disadvantages of using such cells compared to 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 HCN, 12C$_2$H$_2$, 12CO, and 13CO can together span over 120nm 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.