"Astrocomb" opens up new horizons for the planet-hunting telescope

NIST physicist Scott Diddams examines the NIST frequency comb designed to ensure the accuracy of stellar light analysis at the Hobby-Eberly telescope in Texas. Credit: NIST

The hunt for Earth-like planets, and perhaps even extraterrestrial life, has become more accurate thanks to record measurements of starlight made possible by an astrocomb of the National Institute of Standardization and technology (NIST).

The NIST custom frequency comb, which accurately measures frequencies, or colors, of light, ensures the accuracy of stellar light analysis with the help of an instrument called spectrograph located in the Hobby-Eberly telescope, Texas. The project is a collaboration between NIST, the University of Colorado at Boulder (CU) and Pennsylvania State University, the main partner of the telescope and spectrograph.

The new comb apparatus provides for the first time the precision necessary for the discovery and characterization of planets in orbit around M dwarf stars, which make up 70% of the stars of the galaxy and are numerous near the Earth, reported the research team in Optica.

"The comb immediately allowed our Penn State colleagues to take action that they could not do otherwise," said Scott Diddams, NIST Associate. "These improved tools should allow us to find habitable planets around the most ubiquitous stars in our galaxy."

The nuclear furnace of a star emits a white light, modified by elements of the atmosphere absorbing some narrow color bands. To search for planets orbiting distant stars, astronomers are looking for periodic changes to this characteristic "fingerprint", ie, very small variations in the apparent colors of starlight. over time. These color swings are caused by the fact that the star is drawn back and forth by the gravitational pull of a planet in invisible orbit. This apparent oscillation is subtle and the measurements are limited by the frequency standards used to calibrate the spectrographs.

Scott Diddams, NIST researcher, discusses frequency combs and their uses, including their application in search of extrasolar planets. Credit: NIST

Hundreds of exoplanets were discovered through oscillation analysis of the stars, but a planet having a mass similar to that of the Earth and gravitating around the right distance to a star – in the so-called "Goldilocks Zone" – is difficult to detect with conventional technology.

Data collected by the NIST-CU-Penn State research team show that the astrocomb will detect earth-mass planets that cause color shifts equivalent to a star wobble. 39, about 1 meter per second, the approximate speed of a person crossing a room, and at least 10 times greater than that previously obtained in the infrared region of the electromagnetic spectrum. Infrared light is the main type emitted by M dwarf stars.

Over the last 20 years, NIST researchers in Boulder, Colorado, were the first to invent and then pioneered the field of optical frequency combs. The comb delivered to Texas is unique in its kind and has about 5,000 "teeth" or specific color calibration points widely spaced. It is adapted to the reading capacity of the Planet Zone Habitable Spectrophotometer from Penn State Finder and covers the target infrared wavelength band from 800 to 1300 nm. With a size of only 60 cm by 152 cm and composed of relatively simple commercial components, the comb is also robust enough to withstand continuous use at a remote site.

By providing tailor-made light to the spectrograph, the NIST comb acts as a very precise rule for calibrating and tracking the exact colors of a star's fingerprint and detecting periodic variations. The comb, manufactured with the new electro-optical laser technology, provides powerful signals at precisely defined target frequencies, which can be traced according to international measurement standards.

The project has been under construction for years. The NIST-CU-Penn State research team conducted a test in 2012 that showed the promise of the new approach. The new comb was delivered and saw the "first light", as they say in astronomy, in February 2018, and runs every night since May 2018. The new comb has a wider light range and is more stable than the previous demo version.

While the idea of ​​using frequency combs to aid in the discovery of the planet has aroused great interest around the world, the new NIST astrocomb is the first to be used at lengths of less than 10 cm. 39, near the infrared wave. Other combs currently operating on a telescope, such as the HARPS (High Precision Radial Planet Finder) in Chile, are dedicated to the measurement of visible light.

Explore further:
& # 39; Star Comb & # 39; joins the quest for planets similar to those of Earth

More information:
Andrew J. Metcalf et al., Near-infrared stellar spectroscopy with a laser-frequency comb, Optica (2019). DOI: 10.1364 / OPTICA.6.000233

Journal reference:

Provided by:
National Institute of Standards and Technology

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