August 20, 2008

Case Western Reserve University researchers making four-dimensional map of Milky Way

Astronomers join new phase of Sloan Digital Sky Survey


Astronomers at Case Western Reserve University are participating in the newest phase of the Sloan Digital Sky Survey (SDSS), the most ambitious survey of the sky ever undertaken.

Located in Apache Point, N.M., the SDSS began mapping the night sky in 2000. The third phase of SDSS began in July 2008 and Case Western Reserve is an active collaborator throughout its six-year agenda, said Heather Morrison, professor and chair of the department of astronomy at the university.

This phase of SDSS is made up of four different projects. Morrison is involved with the Sloan Extension for Galactic Understanding and Exploration (SEGUE) venture.

"Our focus during the first year is on the Milky Way and the stars that make it up, looking at everything in terms of four dimensions," said Morrison. "The fourth dimension in this case is velocity. In addition to seeing how big our galaxy is, we also are looking to calculate how fast its stars are moving."

In addition to Morrison's involvement, Paul Harding, observatory manager at Case Western Reserve and astronomy alumnus Dan Oravetz will be contributing to handling the actual survey operation as well as the science that results from the survey data. The university first joined the SDSS during its second phase, which ended in June 2008.

In the past, star maps were made using 14-inch photographic plates with less than optimal accuracy. The telescope now features a grid of 30 charge-coupled devices (CCDs) that greatly increase the accuracy of the images.

Mapping the stars in the Milky Way, measuring both distance and velocity, also is made much easier than in years past through the use of a highly efficient spectrograph and fiber optic cables attached to aluminum plates, roughly a meter in diameter. Each plate can record data for as many as 650 stars and other celestial bodies.

Precise coordinates for each star to be analyzed are marked on each aluminum plate. Fiber optic cables are attached to each coordinate on the plate and fed to the spectrograph for data analysis. Analyzing the spectra from each star provides its distance from earth and its velocity.

The ability of the 2.5-meter telescope, coupled with a large image camera and seven square degree spectroscopic field, to record so much data about so many objects at one time has redefined what the SDSS is currently surveying.

"When SDSS began in 2000, it primarily looked at different galaxies, rather than individual stars," said Morrison. "But a few fibers were connected to the plates to view what [was] referred to as boring old stars and the exciting results that were obtained changed some minds."

Morrison says that one third of the second phase of the project (SDSS-II), was devoted to looking at individual stars. The first year of SDSS-III will almost completely focus on stars. To date, the survey has mapped approximately one quarter of the sky.

In mapping the Milky Way, Morrison said that researchers are looking at just how far the edges of the galaxy extend. One star so far has been discovered at 200,000 light years away. Morrison hopes to gather data in the next year on stars up to 300,000 light years away.

Morrison, Harding and Oravetz are part of a collaborative research team. The lead investigator on the SEGUE project is Constance Rockosi at University of California, Santa Cruz. Among the other participating institutions are Cambridge University, Johns Hopkins University, Princeton University and University of Chicago.

Once the data gathering phase of SEGUE is completed, three new projects will commence, including one known as BOSS, which will detect and analyze acoustic echoes from the early universe. Idit Zehavi, assistant professor of astronomy at Case Western Reserve, is an active participant on this project.

Funding for the SDSS is provided by the Alfred P. Sloan Foundation, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society and the Higher Education Funding Council for England.

For more information contact Susan Griffith, 216.368.1004.

Posted by: Kimyette Finley, August 20, 2008 03:32 PM | News Topics: Collaborations/Partnerships, College of Arts and Sciences, Faculty, HeadlinesMain, Provost Initiatives, Research, news

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