Earth-based telescopes get better at observing exoplanets

Scientists, including those of Indian origin, have developed a new, low-cost attachment to telescopes that allows previously unachievable precision in ground-based observations of exoplanets. With the new attachment, ground-based telescopes can produce measurements of light intensity that rival the highest quality photometric observations from space. Researchers, including those from Pennsylvania State University in the US, created custom "beam-shaping" diffusers - carefully structured micro-optic devices that spread incoming light across an image - that are capable of minimising distortions from the Earth's atmosphere that can reduce the precision of ground-based observations.

"This inexpensive technology delivers high photometric precision in observations of exoplanets as they transit the bright stars that they orbit," said Gudmundur Stefansson, graduate student at Penn State.
"This technology is especially relevant considering the impending launch of NASA's Transiting Exoplanet Survey Satellite (TESS) early in 2018," said Stefansson, lead author of the research published in the Astrophysical Journal. Diffusers are small pieces of glass that can be easily adapted to mount onto a variety of telescopes.

Because of their low cost and adaptability, Stefansson believes that diffuser-assisted photometry will allow astronomers to make the most of the information from TESS, confirming new planet candidates from the ground. "Beam-shaping diffusers are made using a precise nanofabrication process, where a carefully designed surface pattern is precisely written on a plastic polymer on a glass surface or directly etched on the glass itself," said Suvrath Mahadevan, associate professor at Penn State.

"The pattern consists of precise micro-scale structures, engineered to mold the varying light input from stars into a predefined broad and stable output shape spread over many pixels on the telescope camera," said Mahadevan. The team, including Penn State graduate student Shubham Kanodia, tested the new diffuser technology "on-sky" on the Hale telescope at Palomar Observatory in the US, the 0.6m telescope at Davey Lab Observatory at Penn State, and the ARC 3.5m Telescope at Apache Point Observatory in New Mexico.

In all cases, images produced with a diffuser were consistently more stable than those using conventional methods - they maintained a relatively consistent size, shape, and intensity, which is integral in achieving highly precise measurements. Using a focused telescope without a diffuser produced images that fluctuate in size and intensity.

A common method of "defocussing" the telescope - deliberately taking the image out of focus to spread out light - yielded higher photometric precision than focused observations, but still created images that fluctuated in size and intensity. By shaping the output of light, the diffuser allows astronomers to overcome noise created by the Earth's atmosphere.

"This technology works over a wide range of wavelengths, from the optical - visible by humans - to the near infrared," said Jason Wright, associate professor at Penn State.