The David and Lucile Packard Foundation has awarded a Packard Fellowship for Science and Engineering to Constance Rockosi, assistant professor of astronomy and astrophysics at the University of California, Santa Cruz. The Packard Fellowship, worth a total of $625,000, is one of the nation's most prestigious honors for young faculty members.

Rockosi will receive $125,000 per year for the next five years to support her research on the structure of the Milky Way galaxy. The Packard Foundation awards these fellowships to young scientists and engineers who show exceptional promise and creativity.

Rockosi is interested in the old, distant stars in our galaxy and the clues they hold to the early history of the galaxy's formation. She is coleader of a team of astronomers exploring the structure of the Milky Way galaxy in a project called the Sloan Extension for Galactic Understanding and Exploration (SEGUE). The SEGUE survey--part of SDSS-II, an extension of the original Sloan Digital Sky Survey--is mapping the positions of tens of millions of stars and measuring their motions and chemical abundances.

"The Milky Way is a pretty typical spiral galaxy, so we can study our own galaxy to learn about galaxies in general and how they formed," Rockosi said.

She plans to use the Packard Fellowship to support a new project that will build on the data obtained from SEGUE. Using adaptive optics technology on the Shane 3-meter telescope at UC's Lick Observatory, she will observe selected stars from the SEGUE survey and combine the data from Lick and SEGUE to obtain a complete, 3-dimensional picture of how the stars are moving through the galaxy. This information will enable Rockosi to use the velocities of individual stars and substructures within the galaxy to map its overall size and shape and shed light on its history.

Streams of stars in the Milky Way have been identified as remnants of small companion galaxies that collided and merged with the larger galaxy. Many such mergers are thought to have taken place over the lifetime of the galaxy and are still taking place today. The Sagittarius dwarf galaxy, for example, is in the process of merging with the Milky Way, and spectacular streams of stars stripped away from Sagittarius by its gravitational interaction with the Milky Way have been traced over much of the sky by previous surveys.

Evidence of much older mergers should still be detectable in the form of coherent streams of old stars moving through the galaxy, even if obvious structures can no longer be seen, Rockosi said.

"We are looking for groups of stars all moving with the same motion relative to the rest of the galaxy. Those coherent streams of stars are signatures of the galaxy's formation from smaller building blocks," she said. "I'll use the Lick observations to measure the velocities of streams found by SEGUE and other surveys."

The SDSS instruments can determine a star's velocity along the line of sight of the telescope. To obtain a complete picture of the star's motion in three dimensions, however, astronomers must also measure its motion in the plane of the sky. This requires the sharpest possible images of the star to determine its exact position in the sky and how that changes over time. For distant stars, the change in position, even over a year or two, is so small that it can be obscured by blurring of the star's image in the telescope.

That's where the adaptive optics technology pioneered at Lick Observatory comes in. Adaptive optics (AO) can correct for the blurring of telescope images caused by turbulence in the Earth's atmosphere. Using the AO system on Lick's Shane Telescope, images of stars are so sharp they appear ten times smaller than uncorrected images, Rockosi said.

"Adaptive optics is a fantastic tool and will be very powerful for studying the distant galaxy. This project is an ideal match between the SEGUE survey and the great facilities we have here at Lick Observatory," she said.

Rockosi will use the SEGUE survey to carefully select the most useful targets for follow-up observations at Lick. She said it will take two or three years to obtain the data she needs to determine the three-dimensional velocities of a large number of stars. She can then use those findings to address fundamental questions about our galaxy and the mysterious dark matter that holds it together.

Most of the mass in the universe is dark matter that we cannot directly observe. Every galaxy is surrounded by a halo of dark matter that can only be detected by observing its gravitational effects. Rockosi's precise measurements of stellar velocities will provide a unique set of data that can be used to measure the total mass of our galaxy and the shape of its dark matter halo.

The Packard Fellowship program, established in 1988, provides support for science and engineering researchers early in their careers, allowing them to pursue their research with few funding restrictions and limited paperwork requirements. Every year, the Packard Foundation invites 50 universities to nominate two young faculty members for the fellowships.

The David and Lucile Packard Foundation, based in Los Altos, is a private family foundation created in 1964 by David Packard and Lucile Salter Packard. The Packard Foundation invests in innovative people and organizations to improve the lives of children, enable creative pursuit of science, advance reproductive health, and conserve and restore Earth's natural systems.

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Note to reporters: You may contact Rockosi at (831) 459-5246 or crockosi@ucolick.org.

A photo of Rockosi can be downloaded from the web at http://www.ucsc.edu/news_events/press/photos/