Discovering astrophysical objects — from Earth-like planets, to binary star systems, to black holes — is already difficult, but especially so when trying to detect them using ground-based telescopes, where the atmosphere can absorb and distort light.

That’s one reason that University of Notre Dame researcher Justin Crepp, associate professor in the Department of Physics and Astronomy, and collaborators began designing a new instrument, called iLocater, a decade ago for southeast Arizona’s Large Binocular Telescope (LBT). The fruits of their labor are now starting to be realized. Three recent studies detail the early successes for the new technology.

The first article, published in the Monthly Notices of the Royal Astronomical Society, describes the installation and commissioning in 2024 of a spectrograph named “Lili” — short for little iLocater — a miniature version of the equipment that will be replaced with a full-sized spectrograph later this year. Lili, which receives light from iLocater’s acquisition camera, “de-risked” the project and allowed astronomers to complete the first end-to-end observations. Lili (as well as the future, larger spectrograph), separates light into its rainbow of colors, allowing researchers to study the chemical composition of astrophysical objects.

They were able to accomplish this, according to the second of the three research articles. Scientists confirmed the presence of binary star system 2 Cygni “B”, which they detected in 2019. Binary star systems consist of a primary star and a smaller companion, and iLocater confirmed the association between 2 Cygni B and its primary star, 2 Cygni A, by independently measuring their temperatures using Lili. This confirmed their association and co-evolution.

“We had to acquire a tremendous amount of follow-up data, including spectroscopy, to confirm what we were seeing was a legitimate companion that is gravitationally co-moving with the star,” Crepp said. “What’s great about 2 Cygni, which is a relatively nearby star system in the Cygnus constellation, is that you can see it with the naked eye as a star in the sky.”

The third article, published in Astrophysical Journal, showed how researchers used iLocater to search for black holes and other compact objects such as white dwarfs and neutron stars. In this case, they used iLocater’s imaging and spectroscopic capabilities to characterize closely separated luminous companions, suspected to be gravitationally “tugging” on their parent stars, Crepp said.

iLocater is the first Doppler spectrograph to use the LBT’s adaptive optics system to compensate for atmospheric turbulence. This capability is essential as astronomers try to achieve high-precision radial velocity measurements from Earth. The process is considerably more cost effective than launching a telescope into space, which is usually necessary for clear images because Earth’s atmosphere distorts the light.

The radial velocity method refers to measuring the speed of an object, like a star or planet, as it moves towards or away from the observer along his or her line of sight, using the Doppler shift of light. This is one of the primary techniques that exoplanets have been discovered in the past; but the method has not yet become sensitive to Earth-like planets.

Now that iLocater is producing scientific results, Crepp looks forward to the installation of the full-sized spectrograph at the end of this year.

“What is really exciting is that iLocater’s final spectrograph will offer 100 times higher resolution than what we used with the initial Lili experiments,” Crepp said.

These first publications and the project have “taken a very long time,” Crepp said. “I was an assistant professor here in 2012 when I originally had the idea, the conception of iLocater. You have to be brave enough to operate on these longer time scales where you're taking on technical risks and opportunity cost, so we had to weigh and balance all of those things.”

Crepp and Jonathan Crass, adjunct assistant professor at Notre Dame (iLocater’s instrument scientist who is now based at Ohio State University), conducted research with iLocater that led to the three scientific papers, working alongside other investigators at Durham University and Ohio State University.

As new hardware comes online and iLocater scientific activities continue to ramp up, the instrument will be used not only by Notre Dame but also by an international consortium of astronomers, including researchers from Italy and Germany, as well as the LBT’s broad domestic partnership, Crepp said.

The project was funded by grants from the National Science Foundation, NASA, and the Mt. Cuba Foundation.

"We deeply appreciate the support provided by NASA (Goddard Space Flight Center and the Jet Propulsion Laboratory) for help with developing key iLocater technologies, as well as the NSF for their essential funding of students, postdocs, and staff,” Crepp said. “We would also like to acknowledge the Mt. Cuba Foundation for their support of iLocater's wavelength calibration unit.”

Originally published by Deanna Csomo Ferrell at science.nd.edu on April 11, 2025.