GRACES

GRACES. The Gemini Remote Access to CFHT ESPaDOnS Spectrograph is a unique astronomical instrument that combines the large light-collecting area of the Gemini North telescope with the high-resolution spectrograph ESPaDOnS at the neighboring Canada-France-Hawaii Telescope. This fiber-optic link enables detailed studies of stellar atmospheres, exoplanets, and galactic archaeology by providing exceptionally high-quality spectra. Its development was a collaboration between the National Research Council (Canada), the French National Centre for Scientific Research, and the international Gemini Observatory partnership.

Overview

The instrument was conceived to leverage the complementary strengths of two major facilities on Mauna Kea. By feeding light from the 8-meter Gemini North mirror through a 270-meter optical fiber to the bench-mounted ESPaDOnS spectrograph, astronomers overcome limitations typically faced by instruments mounted directly on large telescopes. This setup, operational since 2015, provides a stable environment for the spectrograph, crucial for precise measurements of stellar radial velocities and magnetic fields. The project involved key institutions like the Université de Montréal and the Observatoire de Paris and has been used in numerous large surveys, including contributions to the NASA TESS mission follow-up programs.

Instrument Design

The core of the design is a 270-meter-long, fluoride-based optical fiber bundle that runs through an underground conduit between the two telescopes. This fiber efficiently transmits light from the Gemini North Cassegrain focus to the thermally stabilized room housing ESPaDOnS at the Canada-France-Hawaii Telescope. The system includes sophisticated injection optics and calibration units at Gemini North, such as a Fabry–Pérot interferometer for precise wavelength calibration. The spectrograph itself, renowned for its polarization capabilities, was built by a team led by the Laboratoire d’Astrophysique de Marseille and can achieve a spectral resolution of up to 65,000 across the entire optical wavelength range.

Scientific Capabilities

GRACES excels in high-resolution spectroscopy, enabling the detection of subtle chemical abundance variations in stars, which inform studies of galactic evolution and nucleosynthesis. It is particularly powerful for characterizing exoplanet atmospheres through transmission spectroscopy and for measuring stellar magnetic fields via the Zeeman effect. The instrument has been pivotal in follow-up observations for missions like Gaia (spacecraft) and Kepler (spacecraft), helping to determine precise stellar parameters and confirm exoplanet candidates. Its stability also makes it ideal for monitoring radial velocity variations in stars hosting planets discovered by the K2 mission.

Operational History

First light was achieved in August 2015 following commissioning led by scientists from the National Research Council Canada's Herzberg Astronomy and Astrophysics Research Centre. The instrument quickly became a workhorse for the Gemini Observatory, with time allocated through competitive peer review by agencies like the National Science Foundation and the Science and Technology Facilities Council. It has undergone several software and hardware upgrades to improve fiber transmission efficiency and observational flexibility. Notable observing campaigns have included large programs targeting metal-poor stars in the Milky Way halo and detailed studies of stars in open clusters like the Hyades.

Key Discoveries

Research using GRACES has led to significant findings in stellar astrophysics and exoplanet science. It provided crucial chemical evidence for the accretion of a dwarf galaxy, likely Gaia-Enceladus, by the early Milky Way. The instrument has measured detailed abundances of elements like lithium and europium in ancient stars, informing models of the early universe. In exoplanet research, it has helped characterize the atmospheres of hot Jupiter-sized worlds and validated terrestrial planet candidates from the TESS mission. Studies of magnetic activity in solar-type stars have also contributed to our understanding of stellar cycles and space weather.

Category:Astronomical instruments Category:Gemini Observatory Category:Optical telescopes