Professor wins grant to calculate astronomical distances

An astrophysicist at SUNY Oswego is part of an international team of three scientists who will perform the first uniform analysis of a set of data generated by the Hubble Space Telescope, giving the astronomical community a resource for many new investigations.

“One of the fundamental problems in astronomy is how far away stars are,” said Dr. Shashi Kanbur of the physics department. He and his colleagues will answer that question for a particular kind of star, Cepheid stars, in 22 nearby galaxies observed by the Hubble telescope.

While others have studied many of the Cepheids using different techniques, Kanbur said, no one has applied the same technique to all of them. “We will show how far away these galaxies are,” he said, “and how accurately we know that distance.”

He has received a $20,025 grant from the Space Telescope Science Institute to perform his share of the work at Oswego. “You just need a fast computer and an Internet connection” along with the statistical techniques and special software that his team has developed, Kanbur said.

His co-investigators are Dr. Doug Leonard at the California Institute of Technology and San Diego State University and Dr. Nial Tanvir of the University of Hartfordshire in England.

“We have different specialties that all contribute to the project,” Kanbur said. “My expertise is the statistical analysis and the astrophysics.”

Cepheid stars provide a key to astronomical distances because “they pulsate like a heart,” Kanbur explained, “and their brightness changes in a very regular pattern.” The pattern correlates to their actual brightness, so that a Cepheid star that is known, by its pattern, to be very bright but appears dim in the Hubble pictures is also known to be distant.

Kanbur and his associates have developed and are refining “an automatic way to look at these pictures and extract from them the stars which are Cepheids” and to determine the pattern of their pulsating and their apparent brightness, leading to a calculation of their distance. The three scientists worked on developing the technique in an earlier project studying just one galaxy.

In their technique, the element of human observation and judgment will be removed. Their calibration of the Cepheid distance scale will provide a new level of uniformity and objectivity.

“There is a lot of work to get the program to that automatic level,” Kanbur added.

The automation will allow them to sift through the huge amount of Hubble data: images of over two million heavenly objects. Kanbur estimated the project would take between one and two years.

The results of their work will be useful in many future scientific investigations, including stellar population studies and estimates of the Hubble constant—the expansion rate of the universe.

Kanbur joined Oswego’s physics department as an assistant professor this fall. He earned his doctorate in astrophysics at the University of London in 1989 and then conducted research at the University of Glasgow and the University of Massachusetts at Amherst.

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(Posted: Nov 30, 2005)