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

TL;DR

This paper investigates using commercial molecular absorption gas cells as a stable wavelength reference for high-precision near-infrared radial velocity measurements, offering a practical alternative to traditional calibration sources.

Contribution

It demonstrates that commercially available gas cells are viable for wavelength calibration in the near-infrared, providing an effective and accessible method for high-precision spectroscopic surveys.

Findings

Gas cells provide acceptable calibration accuracy in the H band.

Four standard gas cells cover over 120nm of the H band.

Isotopologues can extend wavelength coverage and line density.

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.