Broadband near-infrared astronomical spectrometer calibration and on-sky validation with an electro-optic laser frequency comb

TL;DR

This paper introduces a broadband near-infrared electro-optic laser frequency comb for high-precision spectrograph calibration, validated through on-sky observations, enabling detection of Earth-like exoplanets and detailed spectrograph analysis.

Contribution

It presents a novel, simple, and robust electro-optic frequency comb system for precise wavelength calibration in near-infrared astronomy.

Findings

Achieved <10 cm/s calibration precision on GIANO-B spectrometer.

Validated on-sky performance with a standard star and atmospheric features.

Provided detailed insights into spectrograph inhomogeneities and drifts.

Abstract

The quest for extrasolar planets and their characterisation as well as studies of fundamental physics on cosmological scales rely on capabilities of high-resolution astronomical spectroscopy. A central requirement is a precise wavelength calibration of astronomical spectrographs allowing for extraction of subtle wavelength shifts from the spectra of stars and quasars. Here, we present an all-fibre, 400 nm wide near-infrared frequency comb based on electro-optic modulation with 14.5 GHz comb line spacing. Tests on the high-resolution, near-infrared spectrometer GIANO-B show a photon-noise limited calibration precision of <10 cm/s as required for Earth-like planet detection. Moreover, the presented comb provides detailed insight into particularities of the spectrograph such as detector inhomogeneities and differential spectrograph drifts. The system is validated in on-sky observations of a radial velocity standard star (HD221354) and telluric atmospheric absorption features. The advantages of the system include simplicity, robustness and turn-key operation, features that are valuable at the observation sites.