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Broadband stability of the Habitable Zone Planet Finder Fabry-Pérot etalon calibration system:evidence for chromatic variation



Ryan C. Terrien, Joe P. Ninan, Scott Diddams, Suvrath Mahadevan, Samuel Halverson, Chad Bender, Connor Fredrick, Fred Hearty, Jeffrey M. Jennings, Andrew J. Metcalf, Andrew J. Monson, Arpita Roy, Christian Schwab, Gudmundur Stefansson


The comb-like spectrum of a white light-illuminated Fabry-Pérot etalon can serve as a cost-effective and stable reference source for precise Doppler measurements. Understanding the stability of these devices across their broad (100's of nm) spectral bandwidths is essential to realize their full potential as Doppler calibrators. However, published descriptions remain limited to small bandwidths or short timespans. We present the results of a 6 month broadband stability monitoring campaign of the Fabry-Pérot etalon system deployed with the near-infrared Habitable Zone Planet Finder spectrograph (HPF). We monitor the wavelengths of each of 3500 resonant modes measured in HPF spectra of this Fabry-Pérot etalon (free spectral range = 30 GHz, bandwidth = 820 - 1280 nanometers), leveraging precise cross-calibration with an electro-optic frequency comb reference. The result is an accurate, uniquely extensive spectral and temporal description of this Fabry-Pérot system's resonant mode wavelengths, revealing chromatic structure in their locations as well as in their evolution with time. When averaged across the full 460 nm bandwidth, our measurements show a slow drift on the order of 2 cm s 􀀀1 d􀀀1. However, we also observe variations from this mean drift with amplitudes up to 5 cm s 􀀀1 d􀀀1 in specific spectral regions. We discuss these behaviors in the context of the Fabry- Pérot etalon mirror dispersion and other optical properties of the system, as well as the implications for the use of similar Fabry-Pérot etalons for long-term precise stellar Doppler measurements. Our results show that this system alone supports the wavelength calibration of HPF at the . 10 cm s􀀀1 level over a night and at the . 30 cm s􀀀1 level over 10 d. Our results also highlight the need for long-term and spectrally-resolved study of similar systems that will be deployed to support Doppler measurement precision approaching 10 cm s􀀀1.
Astronomical Journal


astronomy, etalon, frequency comb, exoplanet, spectroscopy


Terrien, R. , Ninan, J. , Diddams, S. , Mahadevan, S. , Halverson, S. , Bender, C. , Fredrick, C. , Hearty, F. , Jennings, J. , Metcalf, A. , Monson, A. , Roy, A. , Schwab, C. and Stefansson, G. (2021), Broadband stability of the Habitable Zone Planet Finder Fabry-Pérot etalon calibration system:evidence for chromatic variation, Astronomical Journal, [online],, (Accessed December 1, 2021)
Created July 8, 2021, Updated October 14, 2021