In January, Canada-France-Hawaii-Telescope (CFHT) accepted the delivery of a brand new instrument – SPIRou for short. Astronomers hope to use the instrument to discover an Earth-like planet around a small, red star.
SPIRou takes the light from a single star and breaks the light down into its component rainbow called a spectrum. The spectrum contains critical information about the star; its composition, temperature, distance and if planets orbit the star.
Planets, including those in our solar system, orbit their star due to the star’s immense gravity. However, the planets also exert a small gravitational force on the star that cause a small change to the star’s motion. Astronomers see this change in motion as a wiggle in the star’s spectrum and can use this motion to infer the presence of planets.
The size of a star’s wiggle is determined by two factors: the planet’s distance from the star, and its size. Large, close planets cause the largest wiggle, so it’s not a coincidence that astronomers have discovered more of these planets than smaller, Earth-like planets. SPIRou hopes to detect a motion as small as 1 m/s or 2.5 mph in a star.
The size of the star also influences the size of the wiggle. The gravitational pull from planets causes a smaller wiggle when orbiting a large star than from the same size planet orbiting a smaller star. This is one of the reasons that astronomers will use SPIRou to observe smaller, redder stars. SPIRou operates in the infrared (IR) wavelength of light. For example, our eyes cannot see in the IR, but we feel the sun’s IR light as heat. The smaller, redder stars observed by SPIRou emit much of their light in the IR wavelengths.
SPIRou arrived in 13 boxes from France in the middle of a pretty snowy January. In short order the boxes were unpacked and the instrument assembled. The first step was to align all of the instrument’s optics: the prisms, mirrors and diffraction gratings that will break the starlight into the spectrum.
The second step was cooling the camera. SPIRou and all IR cameras must be cooled to a very low temperature, on the order of 80Kelvin (-316 F). The camera’s job is to detect heat from space. If the camera is warmer than the light it is looking to detect then it cannot see the light. More importantly to achieve the sensitivity needed to find planets, the instrument’s temperature must be stabilized at a few miliKelvin. To achieve this frigid and stable temperature, the instrument is housed in a cryostat. SPIRou’s optical components slide into a large metal cylinder. This cylinder is a cryostat. The cryostat is pumped to a near vacuum and cooled with liquid helium creating the temperatures needed for SPIRou. The team tested these components in early March.
We had more excitement in late March when SPIRou’s Hawaii 4RG detector arrived. The Hawaii 4RG detectors are cutting edge in infrared detector technology and operate similar to a digital camera, except they will record the spectrum instead of a picture of the star. SPIRou’s 4RG is the only one on Maunakea and possibly the only one that will be doing astronomical research this year. For reference, the soon-to-be-launched James Webb Space Telescope is using Hawaii 2RG detectors, the previous generation of cameras. SPIRou’s technology is more advanced than what NASA is using in its latest space telescope.
The next SPIRou engineering run is scheduled for later this week. Stay tuned for more future updates.