The National Science Foundation (NSF) Major Research Instrumentation Program awarded Georgia State University a $1.39M grant for upgrades to its Center for High Angular Resolution Astronomy (CHARA) Array located at Mount Wilson Observatory in Southern California.
The array consists of six synchronized telescopes, each with a one-meter diameter light-collecting mirror, spread across the mountaintop. These telescopes each send light to a central laboratory, where it is combined — a process known as interferometry — to simulate the resolution of a telescope with a 300-meter light-collecting mirror; the resulting images are produced in great detail.
The upgrades to the array include optical equipment in the telescopes, controllers and a sensitive star tracking detector camera. Once the upgrades to enhance observation are completed in 2028, the facility will be able to detect stars across the visible and near-infrared spectrums.
Gail Schaefer, Ph.D., director of the CHARA Array since 2022 and associate director for three years prior to that, is excited for the discoveries to be made with the enhancements.
Recent collaborations with researchers from the University of Michigan, the University of Exeter in the United Kingdom and the Université de la Côte d’Azur in France look to be enhanced with these upgrades, Schaefer said.
“[The researchers] have built these six telescope imaging combiners; some of [the combiners] work in the near-infrared and some of them in the visible wavelengths,” Schaefer said, referring to light spectrums. “What we would like to do is collect data across the visible and near-infrared wavelengths simultaneously, and this new grant allows us to do that more easily than we currently do.”
This will allow researchers to know the structure of stars better than they currently do. As we observe the edges of a star, the light becomes fainter and harder to detect — an effect called limb darkening, Schaefer said.
“Being able to record different colors of light at the same time allows you to know the structure of the star really well,” Schaefer said. “That helps us in particular when a star has an exoplanet around it, and crosses the surface of the star, it’ll block out light, but as it goes across the surface — depending on what the surface of the star looks like — you can better characterize the planets that are blocking the light.”
Recording at different wavelengths will also allow certain surface features to be recorded more easily, like “star spots,” which we commonly refer to as sunspots.
Aside from recording multiple wavelengths simultaneously, another upgrade, the new star tracking instrument, will allow her and her team to research even fainter stars due to the added stability of the tracking system, Schaefer added.
“The surface tracking camera basically just picks up part of the light and makes sure that the star stays centered on the science instrument,” Schaefer said.
CHARA is one of the few facilities in the world with its capabilities; the Very Large Telescope Interferometer (VLTI), part of the European Southern Observatory’s Very Large Telescope facility, is located in the Southern hemisphere in Chile and operates similarly, albeit with larger telescopes and higher sensitivity, with CHARA having higher angular resolution. The Navy Precision Optical Interferometer (NPOI), in Arizona, historically performed science observations with similar techniques, too, and the Magdalena Ridge Observatory had its first telescope of its array installed in 2018, with the second one coming online in 2023.
So while CHARA doesn’t stand alone, it is by any measure unique and critical to astronomers around the world. Moreover, with an open access policy, CHARA allows researchers around the world to apply for time to use its facilities and features.
“It’s a really unique facility to actually be able to see what stars actually look like, rather than just being pinpoints of light in the sky,” Schaefer said.
Science funding from the NSF has been at the heart of the CHARA Array since its inception. CHARA itself — the center, not the array — has been around since 1984, when it was established with the goal of “promoting, designing, funding and operating a major new instrument capable of achieving new levels of angular resolution” according to the CHARA website.
That instrument would eventually manifest as the CHARA array when the center received seed funding for planning activities in 1985, followed by funding for engineering studies in 1992. The NSF later funded the initial $5.6-million cost to build the array of five telescopes, with construction breaking ground in 1996; two years later, it received funding for an additional sixth telescope from the W.M. Keck Foundation. By 2004, CHARA had all six telescopes synced up and had begun routine science observations.
In the years since, the NSF has continued to support the facility financially, allowing for discoveries over the last couple of decades — support that Schaefer is grateful for is still going strong with the latest grant.
“We’re absolutely thrilled this funding went through, and it’s a way to keep CHARA relevant and be able to do cutting-edge science that pushes the field forward,” Schaefer said.
Great article