SALT Commissioning: Unique Proposals, Unique Experiences

Nov 28, 2011

Commissioning Proposals

UW astronomy people are really excited about using the South African Large Telescope (SALT) — so much so that they’ve asked for much more observation time in the coming semester than the 135 hours that are available for UW-Madison.

Fifteen proposals were accepted to use the UW time. Astronomy graduate students are especially excited about the telescope’s new capabilities.

Third-year graduate student Greg Mosby is enthusiastic about using the new Robert Stobie Spectrograph (RSS) to better understand how massive galaxies are influenced by the supermassive black holes lurking at their centers. This fall, he is undertaking a pilot study focused on three powerful quasars, powered by black holes, that are actively feeding on gas and shining brightly. Greg will take advantage of RSS’s impressive sensitivity to probe the faint outskirts of the quasar host galaxies that are less affected by the glare from the quasars. He aims to test a popular theory that mergers between galaxies trigger both black hole activity and bursts of star formation. “It’s exciting to start my National Science Foundation Fellowship work on a telescope that’s so important to our department,” says Greg.

Fourth year graduate student Corey Wood’s proposal takes advantage of a novel mode of RSS called a Fabry-Perot. It will enable him to map the structure and velocity of highly ionized oxygen gas surrounding five quasars. This gas is believed to have been violently expelled from the quasar host galaxy by an abrupt increase in star formation and black hole activity triggered by a merger between two galaxies. “SALT’s Fabry-Perot capability enables us to observe a spectral line at each position of the extended ionized gas cloud across a wide field of view,” says Corey.

John Chisholm, a second-year graduate student, proposes to use RSS to observe an extremely unusual galaxy culled from a survey of several hundred thousand distant galaxies. The galaxy is remarkable because of the strong and broad lines of highly ionized oxygen and neon in its spectrum, indicating very energetic processes in the galaxy. “SALT’s superior collecting area and advanced spectrograph enable an extremely deep, high quality spectrum of this faint galaxy to be taken in a short amount of time,” says John.

A list of accepted SALT proposal titles and descriptions will be posted at (Click on Our Science, Research Observatories, South African Large Telescope.)

Commissioning Experiences

Astronomy Department scientists Eric Hooper, Ken Nordsieck and Marsha Wolf have returned from South Africa, where they were placing the new Robert Stobie Spectrograph back on the Southern African Large Telescope (SALT) and commissioning the instrument this past (northern) spring. Here they share some of their experiences.

Ken Nordsieck spent more than three months at the SALT site, preparing the instrument to be put on the telescope. “Lifting the instrument on April 9 was a spectacular milestone,” he says. Within two days, they had a second light image of the biggest globular cluster in the Milky Way. “Within a week, a rare stellar explosion of T Pyxidis occurred, its first outburst since 1967. It was an ideal ‘commissioning lamp.’ This convinced me that I have the right religion,” says Ken. He got very little sleep working on the telescope and then the instrument. On a regular basis, he stayed up all night and then worked with the day crews. “But it was all worth it,” he says. “It’s fun to get complex, unique modes working.”

On his first trip, Eric Hooper was supposed to commission the multi-object spectroscopy mode (MOS) of RSS but never got to do it because, just after lifting the instrument, he was enlisted to test and calibrate other instrument modes. When he returned to South Africa in August, he worked on the multi-object mode, helping to bring it from a barely functional state to nearly ready for full-scale operation. “It was cowboy astronomy. We’d come up with simple solutions and hope they’d work,” says Eric. “It was nonstop, with no breaks. I worked my tail off but had a blast because of the people I worked with. It was fun being at the site.”

Marsha Wolf’s primary involvement was commissioning the Fabry-Perot mode of the RSS. She worked with Ted Williams of Rutgers University, the project scientist for this capability, in preparation for building a similar mode into a new near infrared instrument for SALT being built at UW. They worked through a lot of bugs and saw a lot of progress. “It was challenging to get the different software and computer systems to work together. Commissioning is hard work, but very rewarding when everything finally works,” says Marsha. “It was pretty cool to see the different parts of a galaxy light up as we stepped through the wavelengths.”


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