Spectrograph optics enable recording of faint stars

27th July 2020
Alex Lynn

Optical Surfaces has reported delivery to the Research Institute in Astrophysics and Planetology (IRAP) of high precision disperser prisms and folding mirror components that lie at the heart of the SPIRou / SPIP near infrared spectrograph.

The SPIRou / SPIP spectrograph is designed to be able to record the whole near infrared spectrum of a star (over the wavelength range 0.98 to 2.35µm and in either circular or linear polarization) on a 16-million-pixel Hawaii 4RG detector in a single exposure. In addition to being a spectropolarimeter, separating the light from stars into its elementary colours and vibration modes, SPIRou / SPIP is a high-precision velocimeter, capable of recording the tiny motions of a star that indicate the presence of an orbiting planet.

As a consequence, the SPIRou/SPIP spectrograph will be used to also hunt for Earth-like planets orbiting in the habitable zones of nearby red-dwarf stars. IRAP (Toulouse, France) is one of the six laboratories which form the Midi-Pyrénées Observatory.

Yoan Micheau, a research engineer at OMP (Midi-Pyrénées Observatory), commented: "Our innovative SPIRou / SPIP spectrograph is contained within a large cryogenic Dewar cooled down at a temperature of 77K (-200 °C) making it thermally stable to within a few millikelvin. To give us the best chance of recording faint astrophysics phenomena places great demand on the precision and accuracy of the spectrograph optics we use.

“Having successfully worked with Optical Surfaces Ltd on previous optically demanding projects it was an obvious choice to work with them again. I am very pleased to say that they have manufactured and delivered the large folding mirror and Infrasil / Zinc Selenide disperser prisms to the very demanding specifications (surface quality, transmission, wavefront error, scattered light and planarity) that we set."

Dr Aris Kouris added: “Having supplied similar optics for the successful ESPaDOnS, FEROS and SPIRou projects, we have a proven record in manufacturing, mounting and testing precision optics for astrophysics projects”. He added “The high spectral resolution and performance that the SPIRou / SPIP spectrograph is designed to deliver can only be achieved by using optical components of the highest quality.”

The scientific objectives of Midi-Pyrénées Observatory are to study and develop understanding of the Universe including the Earth as a planet, its ionized environment, the sun and its planets, the stars and their planetary systems, the galaxies, the very first stars and the primeval Big Bang. The Midi-Pyrénées Observatory is acknowledged as a leading European centre of excellence in ground-space astrophysics.

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