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NMSU astronomers use powerful instrument to see through the dust for the stars

While we know that the sun is one of billions of stars that make up our Milky Way galaxy, there are still many mysteries about how our galaxy formed.

Equipment being lowered at a telescope
After delivery from the University of Virginia instrument lab to the Sloan 2.5-m Telescope in New Mexico (in the building to the left), the 2-ton APOGEE spectrograph is lowered to a dedicated laboratory in an adjacent bulding. Optical fibers forty meters long transmit the light collected by the telescope to the instrument for several hundred stars at a time (Photo courtesy of the APOGEE team)

Some clues about the formation of the galaxy exist in the details of what stars are made of and how they are moving, but obtaining information on this is complicated because the majority of the stars in the disk of the Milky Way are obscured by clouds of interstellar dust, preventing us from seeing them. Now a new and powerful instrument is starting to open up views of large numbers of previously obscured stars.

For almost a year, New Mexico State University astronomers, along with collaborators from member institutions around the world, have been using the 2.5-meter telescope at Apache Point Observatory to study the stars in the Milky Way as part of the Sloan Digital Sky Survey III project with the hope of one day making a three dimensional chemical map of the galaxy.

With the Apache Point Observatory Galactic Evolution Experiment, researchers are cataloging data on 100,000 stars - mostly within the disc of the Milky Way - to determine what the stars are made of and to precisely measure how fast the stars are moving toward or away from Earth.

"One challenge of studying Milky Way stars is that most of them lie in a relatively flat disk where there is also a lot of obscuring dust that blocks our view," said Jon Holtzman, head of the Department of Astronomy and a principal investigator of APOGEE.

The APOGEE instrument is looking at individual stars, but it is looking at them not in optical light that the human eye can see, but in infrared light.

"One nice property that infrared light has is it is better able to penetrate the dust that is in the disk of the Milky Way than optical light is, so you can see stars that are behind more clouds of dust," Holtzman said.

The APOGEE instrument takes light from the stars and splits it up into its constituent infrared components. The process is similar to a prism making a rainbow of light but APOGEE works in the infrared part of the spectrum. Using the resulting spectra, APOGEE can map the distribution of chemical compositions and radial velocities across much of the disc of the Milky Way.

Holtzman said NMSU is taking a lead role in extracting and calibrating the spectra from the raw data gathered daily from the APOGEE instrument so that other researchers can do a chemical abundance analysis.

Nine months into the APOGEE project, researchers have gathered data on tens of thousands of stars, largely because the new state-of-the-art instrument can take spectra of 300 stars at a time. At this point, researchers have already collected more infrared high-resolution spectra of stars than have been collected by all other telescopes combined.

"The eventual goal is to make a map of what the chemistry of stars in the Milky Way looks like as a function of its location in the galaxy. That tells you something about how the galaxy was put together," Holtzman said.

The data gathered will be available to other researchers as well as the general public.

The overall goal of the current phase of the Sloan survey is to study the distribution of massive galaxies in space, learn about the structure and formation of our Milky Way galaxy and initiate a search for massive planets orbiting other stars. SDSS III began in 2008 and is slated to run until 2014. The project cost will be about $44 million.

Holtzman said astronomers are already considering how they can continue to use the APOGEE instrument after 2014. Some ideas being considered are to extend the data gathering to include hundreds of thousands of stars, as well as to duplicate the instrument and to place the copy in the southern hemisphere so astronomers can view stars not visible from the Northern hemisphere.

The Apache Point Observatory is located in the Sacramento Mountains, about 20 miles south of Cloudcroft, and is within the Lincoln National Forest. Four telescopes are operated at the site: the 3.5-meter Astrophysical Research Consortium telescope; the 2.5-meter telescope of the Sloan Digital Sky Survey; the 1.0-meter NMSU telescope; and a 0.5-meter telescope.