Regional
12:11 pm
Mon August 26, 2013

NMSU Astronomers Unlock Mysteries Of The Milky Way

After more than two years of study, astronomers from New Mexico State University, along with collaborators from around the world, released the first data gathered by the Apache Point Observatory Galactic Evolution Experiment (APOGEE).

NMSU astronomers and partner groups have been studying the stars in the Milky Way with the 2.5-meter telescope at Apache Point Observatory in the Sacramento Mountains as part of the Sloan Digital Sky Survey III project, with the hope of someday making a three-dimensional chemical map of the galaxy.

"This experiment aims to try to learn more about the formation of our galaxy (the Milky Way) by studying the compositions of a large number of individual stars from different regions of the Galaxy," said Jon Holtzman, astronomy professor and department head in NMSU's College of Arts and Sciences, who led the effort to prepare the APOGEE data for Data Release 10. 

Data Release 10 was unveiled in late July. The data include infrared stellar spectra of 60,000 stars. 

"A star's spectrum is a powerful tool for learning about the star -- it tells us key details about the star's temperature and size, and what elements are in its atmosphere," Holtzman said. "It's one of the best tools we have for learning about stars, like getting a photo of someone instead of just knowing their height and weight."

The state-of-the-art APOGEE instrument takes spectra of about 250 stars at a time, leading to the collection of data for about 2,000 stars on a good night. It takes light from the stars and splits it up into its constituent colors. The process is similar to a prism making a rainbow of light but APOGEE works in the infrared part of the spectrum. Infrared light is able to better penetrate the dust that is found in the disk of the Milky Way, allowing astronomers to view stars that are obscured in visible light. 

"The Milky Way has several different components: a relatively flat disk of stars, a central bulge or bar, and a diffuse halo of stars," Holtzman said. "It is not yet clear how and when these different components were assembled, and the length of time it took for each component to form." 

With the Apache Point Observatory Galactic Evolution Experiment, researchers are cataloging data on 100,000 stars over three years - 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.

"As the galaxy which we can study in the most detail, the Milky Way is likely to provide key clues about how galaxies -- which are the building blocks of the Universe -- were assembled," Holtzman said. "APOGEE is particularly exciting to me because it is working in a research area in which I'm really interested: the interface between studies of individual stars and studies of galaxies. NMSU is heavily involved in this project; several graduate students are playing important roles."

NMSU astronomy graduate students working on various aspects of data analysis agree the observations released in DR10 provide a one-of-a-kind picture of how the Milky Way is put together and feel fortunate to be involved in the project. 

"I reduce the APOGEE observations on a daily basis, which transforms the data into a format the science teams can use," said Michael Hayden, one of the graduate students working on the project. "I then upload information on which stars' observations are complete so that the staff at Apache Point Observatory know which areas of the sky no longer need to be observed."

"Probably my biggest scientific contribution is analyzing the kinematics and stellar populations of the Sagittarius Dwarf Spheroidal Galaxy, which resulted in a scientific paper that should be out later this year on which I was second author," said Sten Hasselquist, astronomy graduate student.

Graduate student Diana Feuillet's work with APOGEE involves collecting calibration data and analyzing that data separately from the APOGEE analysis, to make sure that APOGEE analysis is producing reasonable answers.

"With the data collected, the team is able to determine detailed information about the stellar atmospheres," Feuillet said. "Such a large, homogeneous data set is crucial to exploring how the galaxy evolved."

Holtzman said astronomers are already looking at ways to continue using the APOGEE instrument after 2014, when the current phase of the Sloan Digital Sky Survey will end.

"We plan to build another APOGEE instrument or move the existing one so that we can extend our view by collecting data at a telescope in the Southern hemisphere, where different regions of the Milky Way can be seen better than they can from Apache Point Observatory."

Data Release 10 also includes an additional 684,000 new spectra from the Baryon Oscillation Spectroscopy Survey (BOSS) 1000-fiber spectrograph. This and future data from galaxies and quasars will help researchers in understanding "dark energy," the invisible matter scientists believe makes up about two thirds of the universe. 

Data Release 10 is available to the general public as well as researchers at http://www.sdss3.org/dr10/.

The Apache Point Observatory is located 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.