A Spectrograph - or Three - of One's Own

August 1, 2011

In addition to partnering on Large Binocular Telescope and the 2.4-meter telescope at MDM observatory in Arizona, the Imaging Sciences Lab has developed a number of important astronomical instruments over the last ten years. As a result, Ohio State has become one of the leading universities for the design and construction of astronomical instrumentation for ground-based telescopes.

Enter Associate Professor Paul Martini, who primarily studies galaxy clusters, but also began to work on instrumentation during his postdoctoral research. Now at Ohio State, when he found himself in need of a new instrument, he proceeded to design and build his own.   

While this impressive feat kept him and his colleagues busy for several years, this spectrograph – the first of three – has greatly helped Martini to further his understanding of galaxy formation and evolution.

Photo of two merging galaxies taken by OSMOS.The Ohio State Multi-Object Spectrograph, or OSMOS, was initially conceived by Martini in 2006 and eventually commissioned at MDM in April of 2010. Compared to traditional spectrographs that are used for gathering data on a single object, OSMOS’s multi-object capability allows it to analyze multiple objects, such as galaxies, simultaneously.  “OSMOS can collect data for tens of galaxies at a time, which makes it possible to study large clusters of galaxies with a single observation,” remarked Martini.

“I chose to design a spectrograph for the 2.4-meter telescope at MDM for two reasons,” said Martini. “The first is because not many multi-object spectrographs are designed for smaller telescopes, yet they are well-suited to the study of nearby galaxy clusters, and the second is that I would be able to observe with the spectrograph more often if it were at MDM because OSU is one of 5 consortium partners with the observatory,” he continued.

A spectrograph is an instrument used to separate light into its individual components, or colors; similar to how a prism disperses light. When an object’s light is split in this manner it creates what is known as a spectrum.

Spectra have been a crucial contributor to astronomy research for nearly two centuries and have been used for uncovering such mysteries as the chemical composition of the Sun as well as the speed with which the Andromeda Galaxy is moving towards the Milky Way. Martini applies the spectra he receives from OSMOS to determine if galaxies are associated with the clusters he studies, and if so measures the rate of star formation in these galaxies and the typical age of their stellar population.

Photo of Paul Martini. “Another key parameter we can measure for galaxies is their chemical composition,” explained Martini. “Armed with this knowledge, we can learn how stellar evolution changes the chemical makeup of galaxies and how galaxies change over time,” he continued.

Due to OSMOS’s success, Martini has been approached by the National Optical Astronomy Observatory to build two more spectrographs. This next generation of OSU instruments will be named the Cerro Tololo Ohio State Multi Object Spectrograph and the Kitt Peak Ohio State Multi Object Spectrograph, or COSMOS and KOSMOS for short – each named for the observatory where it will eventually be installed.

 While verbally distinguishing the names of these instruments might pose a slight challenge, construction of both spectrographs is well under way in the instrumentation labs here at Ohio State.

One of Martini’s colleagues, Rebecca Stoll, has been the primary graduate student involved with the varying aspects of building OSMOS, COSMOS, and KOSMOS. “The great thing about being an astronomer working with the instrument team is that I’ve gotten to dip my toe in a little bit of everything, from construction to testing to being among the first to use the instrument,” she said.

Some of her work with the three spectrographs has included layout design, assembly, and integration of the instrument control electronics.

Photo of OSMOS team. Names from left to right: Ross Zhelem, Paul Martini, Mark Derwent, Rebecca Stoll.“I’ve had the opportunity to work with and learn from a number of the terrific people we have on the instrument team, particularly Mark Derwent, Dan Pappalardo, Dave Brewer, and Dave Steinbrecher,” Stoll remarked. “And the best part is that now that OSMOS is fully operational, I get to use it. I’m now working on my second paper using OSMOS data, and I look forward to continuing to use it while I’m at OSU,” she continued.

Adorned with a block “O” for Ohio State, all three spectrographs are a proud product and symbol of what the Department of Astronomy can do. Although OSMOS is only available to astronomers at institutions that are members of the MDM consortium, any and all astronomers can apply to use KOSMOS or COSMOS through the National Optical Astronomy Observatory beginning in 2012.

Written by Jessica Orwig