UW Spectrograph to Be Commissioned on SALT

Jun 01, 2011

It’s an exciting time for Astronomy Department scientists Eric Hooper, Ken Nordsieck and Marsha Wolf. They’re working in South Africa this spring to place the new Robert Stobie Spectrograph back on the Southern African Large Telescope (SALT) and commission the instrument.

The spectrograph first went on the telescope five years ago. However, more development work was needed for both the telescope and the instrument. At long last, everything is coming together, including soon, light from the most distant galaxies.

“This is big news for the Astronomy Department, the people and government of South Africa, and the consortium of 13 U.S. and international partners involved in the project,” says Hooper. “Astronomy is a major focus of the South African government, and it contributed generously to the project, which has iconic status in South African society.

“Commissioning the spectrograph is like having a custom car and figuring out how it works,” he continues.“It’s a one-of-a-kind custom-made instrument. By calibrating it and seeing what it can do and how well it performs, we’ll come to totally understand it. Other scientists will benefit from knowing its strengths and how to use them, as well as its quirks and how to account for them.”

UW-Madison is a principal partner in the international consortium that runs SALT, one of the world’s largest single optical telescopes and the largest in the Earth’s southern hemisphere. It is located in the South African Great Karoo, an exquisitely dark and dry site south of the Kalahari desert. Using a revolutionary mounting and guiding system, the telescope remains largely stationary, while the instrument platform above the mirror moves in order to track celestial objects across the sky.

“SALT scientists are working together to look at colors of light in new ways,” Hooper explains. “Using a part of the instrument called a Fabry-Perot tunable narrow band filter to finely sub-divide the rainbow of the incoming light, they can take pictures of the
sky in many narrow ranges of color and scan through sub-shades to finely discriminate between structure and details at different wavelengths of light.”

“The telescope has a relatively large field of view, a quarter the size of the full moon, so spectrographic imaging is the wave of the future,” adds Nordsieck. “In addition, the polarization of light will be measured, allowing for the unraveling of magnetic fields and for three- dimensional views of things. There is also interest in high-speed, high-time resolution modes so that, for instance, during an eclipse we can watch the magnetic field change a hundred times faster than ever before and see the details of black holes and white dwarfs.

“The combined operating modes of the spectrograph are like a Swiss army knife with new tools that nobody ever came up with before,” Nordsieck explains. “We will look at things in a new way and see how the modes interact. I’m expecting the unexpected—something spectacular.”

Telescopes like SALT are large enough to peer back in time and study galaxies so distant that they formed shortly after the Big Bang. Because of its southern site, SALT also has one of the best views into the closest galaxies to our Milky Way, the Large and Small Magellanic Clouds. It is able to record distant stars, galaxies and quasars a billion times too faint to be seen with the unaided eye, as faint as a candle flame at the distance of the moon.

The construction of SALT was funded by a consortium of 13 international partners: National Research Foundation (South Africa); University of Wisconsin-Madison; American Museum of Natural History; Carnegie Mellon University; Dartmouth College; Rutgers University; University of North Carolina-Chapel Hill; Consortium of UK Universities and Institutions; Georg-August-Universitat Gottingen (Germany); Hobby-Eberly Telescope Board (international, including Penn State, Stanford University, University of Texas and Georg-August-Universitat Gottingen); Inter-University Centre for Astronomy and Astrophysics (India); Nicolaus Copernicus Astronomical Center (Poland); and University of Canterbury (New Zealand).

UW-Madison Astronomy Home