Stars Wobbling at the Speed of a Desert Tortoise

In recent posts about new observing projects at Kitt Peak National Observatory, I’ve largely focused on the DESI spectrograph which aims to create a three-dimensional map of the northern sky. In fact, I’m in Denver, Colorado this weekend at MileHiCon and I’ll be giving a presentation on this very subject. However, this isn’t the only new instrument I’m helping to deploy and commission.

At the WIYN 3.5-meter we’re installing a spectrograph called NEID. Kitt Peak sits on the land of the Tohono O’Odham people in Southern Arizona. The acronym is derived from the Tohono O’Odham word meaning “to see.” The actual acronym is: NN-EXPLORE Exoplanet Investigations with Doppler Spectroscopy. In other words, it’s an instrument that will be used to look for planets around other stars. Like the DESI spectrograph, fiber optics are mounted to the telescope and feed a spectrograph two floors below the telescope. Just over a week ago, I helped to run the fibers from the point the instrument will be mounted down to the spectrograph room. In the photo, you can see the fiber optic cable laid out like undulating waves at the base of the telescope. The instrument itself will be mounted at the round port that currently has the white, rectangular sign.

The way a spectrograph like NEID finds planets around other stars is by measuring how much they move toward and away from the Earth when they’re pulled by orbiting planets. You likely see spectra all the time. A rainbow is a spectrum of the sun. In a spectrum are characteristic lines caused by elements in the star’s atmosphere. When a planet tugs the star toward Earth, those lines move toward the blue end of the spectrum. When a planet tugs the star away, the lines move toward the red end. Of course, one of the hopes of exoplanet science is to detect Earth-like planets around other stars, or more specifically, Earth-sized planets in the zone around a star where water can be liquid. If you imagine watching our sun from another star, we’d see the Earth pull the sun toward or away from us at about 30 centimeters per second, or about the speed of a desert tortoise!

To see this small motion, you need to be able to see the spectra—the rainbow—at very high resolution. This is more than magnification. You need to see it at great detail. A spectrograph that can do that is often fairly big and it’s very difficult to mount it to the side of a moving telescope. This is why we use a fiber to capture the light and send it to a spectrograph in a different room. This allows the engineers to build the spectrograph as big as they need, but only requires them to mount the fiber to capture the light to the telescope.

Fiber optic cable is meant to be tough, but it can break, so it’s gratifying after we make the run to be able to shine light through the cable and see it at the other end, as we see in this post’s second photo!

Besides looking very specifically for Earth-like planets, the NEID spectrograph will be providing support for NASA’s Transiting Exoplanet Survey Satellite, or TESS, mission, which is searching for exoplanets around the closest stars to Earth. Once TESS discovers a planet, we can observe it with NEID and get more precise mass and density information about the planet. Such measurements help us better understand the composition and formation of the planets around other stars. It’s a very exciting time at Kitt Peak as we deploy these spectrographs which will help us understand both planets in our galactic neighborhood and the overall structure of the universe.

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