It’s a tall order for spectrographs to look at stars thousands of light years away and detect motions slower than the pace of a person walking down the street. High-resolution spectrographs have lowered the exoplanet detection threshold to about a meter per second. But these instruments come with big price tags.
At Yale University, Drs. Debra Fischer and Julien Spronck, along with Dr. Geoff Marcy of the University of California, Berkeley, set out to improve existing spectrograph technologies. Spurred by a $45,000 grant from The Planetary Society, the team built FINDS (Fiber-optic Improved Next generation Doppler Search) Exo-Earths, a spectrograph add-on device.
A telescope collects starlight and focuses it on a lens that leads to a spectrometer. The light must be precisely focused at the center of the lens to obtain consistent, accurate measurements. This means a sudden gust of wind at the observatory or a vibration in the telescope’s guidance system can jiggle the starlight, causing data errors. One way to alleviate these errors is by sending the starlight through a fiber-optic cable. Fiber-optic cables have cores made of glass or plastic. Light entering the cable scatters, emerging into the spectrograph as an even cone. As a result, small telesccope variations won't have such a negative effect on the data. The tradeoff is that some of the starlight will be absorbed by the cable's insulation, but the net result should still be an improvement in resolution.
Working on FINDS
Debra Fischer and Julien Spronck at work on the 1.5 meter telescope at the Cerro Tololo Inter-American Observatory (CITO) in Chile, where they are searching for planets around Alpha Centauri.
The FINDS prototype was a 2-by-1 foot box containing the fiber-optic cable and a system of mirrors and lenses. It was installed on the 3-meter telescope at Lick Observatory near San Jose, California, and saw first light in July 2009. The FINDS team, led by Fischer, measured stars with well-known wobble rates to check the system's performance. The results were promising: FINDS had reduced data errors by 30 percent, with a light loss of just 20 percent.
Fischer and Spronck built another version of FINDS for one of the 10-meter Keck Observatory telescopes in Hawaii. The telescope's design could not accomodate the original 2-by-1 foot box, so Spronck built a tiny 3-by-1 inch version of the technology, which was called Matchbox FINDS.
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