ESPaDOnS

ESPaDOnS. It is a high-resolution echelle spectropolarimeter installed at the Canada–France–awaii Telescope on Mauna Kea in Hawaii. Commissioned in 2005, the instrument is a cornerstone facility for stellar physics, enabling precise measurements of stellar magnetic fields and detailed chemical abundance analyses. Its unique polarimetric capabilities have made it a leading tool in the field of stellar magnetism and have contributed to numerous discoveries concerning stellar evolution and activity.

Overview

ESPaDOnS was designed and built through a collaboration between the Observatoire Midi-Pyrénées in France and the Observatoire de Paris, with significant contributions from Université Laval in Canada. The instrument's primary scientific driver was the need for a high-efficiency, high-resolution spectropolarimeter in the Northern Hemisphere to complement southern instruments like HARPS at the European Southern Observatory. It is permanently mounted at the Cassegrain focus of the Canada–France–Hawaii Telescope, one of the premier observatories within the Mauna Kea Observatories complex. This strategic location provides access to excellent atmospheric conditions, which are critical for its demanding spectroscopic and polarimetric measurements.

Instrumentation

The core of the instrument is a cross-dispersed echelle spectrograph fed by a dedicated polarimetric module. Light from the telescope first enters the polarimeter, which uses a combination of Fresnel rhombs and a Wollaston prism to split the beam into two orthogonal polarization states. These beams are then fed via optical fibers to the spectrograph, which is housed in a thermally stabilized vacuum chamber to ensure exceptional stability. The spectrograph employs a large R2 echelle grating and a cross-dispersing prism to achieve a resolving power of approximately 68,000 across its entire spectral range from 370 to 1050 nm. A large-format CCD detector, specifically a 2048x4608 pixel E2V device, captures the resulting spectrum.

Scientific capabilities and discoveries

Its primary capability is the detection and mapping of stellar magnetic fields through the Zeeman effect, which splits spectral lines in the presence of a magnetic field. This has revolutionized the study of stars like magnetic Ap and Bp stars, solar-type stars, and pre-main sequence objects such as T Tauri stars. The instrument has been pivotal in large-scale surveys like the Magnetic Topologies of Young Stars and the Survival of close-in giant Exoplanets project. Key discoveries include the first detailed magnetic maps of stars other than the Sun, evidence for complex magnetic field evolution in Herbig Ae/Be stars, and crucial data on the role of magnetism in the angular momentum evolution of solar-type stars. It has also been used to characterize the atmospheres of exoplanets and to study chemical peculiarities in Population II stars.

Operational history

Following its commissioning in early 2005, it quickly became one of the most sought-after instruments on the Canada–France–awaii Telescope. It has been used in numerous large international observing programs, including the BinaMIcS project to study magnetism in binary stars. The instrument underwent a significant upgrade in 2015 with the installation of a new detector and improved data reduction pipeline, enhancing its sensitivity and efficiency. Its operational schedule is managed through the telescope's time allocation committee, which receives proposals from the consortium members in France and Canada, as well as from the broader international astronomical community. The data are processed with a dedicated software suite called Libre-ESpRIT, developed at the Observatoire de Paris.

Technical specifications

The instrument covers a spectral range from 370 nanometers in the near-ultraviolet to 1050 nanometers in the near-infrared. It provides a spectral resolving power of about 68,000 in its standard polarimetric mode. In a special "star-only" mode that bypasses the polarimeter, the resolving power can reach 81,000. The polarimetric accuracy is better than 0.01% per spectral bin, which is essential for detecting weak stellar magnetic fields. The typical signal-to-noise ratio achievable per spectral pixel is over 500 for a one-hour exposure on a bright star. The entire spectrograph is maintained under vacuum at a stable temperature to minimize spectral drifts, a critical requirement for precise radial velocity measurements and long-term magnetic monitoring campaigns.

Category:Astronomical instruments Category:Spectrographs Category:Canada–France–Hawaii Telescope