Today, astronomers with the Sloan Digital Sky Survey III (SDSS-III) released a new online
public data set featuring 60,000 stars that are helping to tell the story of how our Milky Way galaxy
formed.
The highlight of today's "Data Release 10" is a new set of high-resolution stellar spectra —
measurements of the amount of light given off by a star at each wavelength — using infrared light,
invisible to human eyes but able to penetrate the veil of dust that obscures the center of the Galaxy.
The data released today includes infrared spectra of these
two stars, shown in the context of the Milky Way galaxy.
The map shows an infrared view of the Milky Way as seen from
Earth. Green circles show areas where Data Release 10 includes infrared spectroscopy data
from the first year of APOGEE observations. The white boxes show the infrared spectra of
two stars as seen by APOGEE; red lines show where these stars live in the Galaxy. The two
spectra are from two stars: one in the galactic bulge that is rich in elements heavier
than hydrogen, and one further out in the disk that has fewer such heavy elements.
Credit:
Peter Frinchaboy (Texas Christian University), Ricardo Schiavon (Liverpool John
Moores University), and the SDSS-III Collaboration. Infrared sky image from
2MASS, IPAC/Caltech, and University of Massachusetts.
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"This is the most comprehensive collection of infrared stellar spectra ever made," said Steven
Majewski of the University of Virginia, the lead scientist for the APOGEE project. "Sixty thousand
stars is almost ten times more high-resolution infrared stellar spectra than have ever been measured
before, by all the world's telescopes. Selected from all the different parts of our galaxy, from the
nearly-empty outskirts to the dust-enshrouded center, these spectra are allowing us to peel back the
curtain on the hidden Milky Way."
The new spectra are the first data released by the SDSS-III's Apache Point Observatory Galactic
Evolution Experiment (APOGEE), an effort to create a comprehensive census of our Milky Way galaxy.
"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," said Jon Holtzman
of New Mexico State University, who led the effort to prepare the APOGEE data for Data Release 10.
"It's one of the best tools we have for learning about stars, like getting someone's fingerprints
instead of just knowing their height and weight."
The question of how our Milky Way galaxy formed has been the subject of scientific speculation
and debate for hundreds of years. APOGEE's three-dimensional map will provide key information for
resolving central questions about how our galaxy formed over the many billions of years of its history.
The Milky Way currently has three main parts: a high-density oblong bulge in the center, the
flat disk where we live, and a low-density spherical component called the "halo" extending out hundreds
of thousands of light years. "Stars in these different regions have different ages and compositions,
which means they formed at different times and under different conditions throughout the history of our
galaxy," says Gail Zasowski, an NSF Postdoctoral Fellow at The Ohio State University who led the
critical effort to maximize APOGEE's scientific potential by selecting the best possible sample of stars.
If you look up at the sky from a dark site, far away from the overwhelming glow of city lights, the
Milky Way galaxy appears as a luminous band across the sky, overlaid with dark curtains. This band is
the disk and bulge of our galaxy, and the curtains are the dust that blocks visible light from more
distant parts of the Milky Way.
Because of this dust, previous studies of stars in the Milky Way have been limited in their
ability to consistently measure stars toward the center of our galaxy. APOGEE's solution is to look
in infrared light, which can pass through the dust. This ability to explore previously hidden regions
of the Galaxy allows APOGEE to conduct the first comprehensive study of the Milky Way, from center
to halo."
Observing tens of thousands of stars is a daunting, time-consuming task. To accomplish its goal
of observing 100,000 stars in just three years, the APOGEE instrument observes up to 300 different
stars at a time using fiber-optic cables plugged into a large aluminum plate with holes drilled to
line up with each star. Light passes through each fiber into the APOGEE spectrograph, where a prism-like
grating distributes the light by wavelength. "The grating is the first and largest of its kind deployed
in an astronomy instrument," said John Wilson of the University of Virginia, who led APOGEE's
instrument design team. "That technology is critical to APOGEE's success."
APOGEE's spectra of stars will help unlock the history of our galaxy, and the key is learning
the compositions and motions of stars in each region. Because elements heavier than hydrogen and helium
were produced in stars and spread through the Galaxy by exploding stars and stellar winds, astronomers
know that stars with more of these heavy elements must have formed more recently, after previous
generations of stars had time to create those heavy elements.
"By finding which parts of the Galaxy contain older versus newer stars, and by putting this
together with how the stars are moving, we can write a detailed history of how the Galaxy formed,
and how it evolved into what we see today," said Peter Frinchaboy of Texas Christian University, who
coordinated all of the APOGEE observations.
APOGEE data also provide a rich context for investigating a wide range of questions about the stars
themselves. Because APOGEE observes each target star several times, it can identify changes in each
star's spectrum over time. This feature has enabled the APOGEE team to discover unusual types of rapidly
variable stars, to pinpoint how many stars are actually binary stars with unseen companions, and even
to detect the subtle stellar motions caused by orbiting planets.
Data Release 10 also publishes another 685,000 spectra from the SDSS-III Baryon Oscillation
Spectroscopic Survey (BOSS). These new spectra come from galaxies and quasars as seen when our
universe was much younger, just as the mysterious force of "dark energy" was beginning to influence
the universe's expansion. The new BOSS spectra, and the additional spectra that the SDSS-III will
continue to obtain in the final years of the survey, will help scientists in their quest to understand
what dark energy might be.
SDSS-III is a six-year survey of nearby stars, the Milky Way galaxy, and the distant cosmos.
The Sloan Foundation 2.5-meter telescope at Apache Point Observatory in New Mexico conducts observations
every night that feed either the BOSS optical or APOGEE infrared spectrograph. "We've been putting
out data releases since 2001, and we're not slowing down yet," said SDSS-III Spokesperson Michael
Wood-Vasey of the University of Pittsburgh. "Public access to data has always been a key goal of our
project, and we're proud to continue that tradition today with this new release rich with information
about our own galaxy." All of these data are available to the public, free of charge, at
http://www.sdss3.org/dr10.
A photo of four SDSS-III scientists working on the APOGEE
spectrograph.
Left to right: Garrett Ebelke (Apache Point Observatory),
Gail Zasowski (The Ohio State University), Steven Majewski (University of Virginia)
and John Wilson (University of Virginia). Majewski is actually standing across the room;
he appears here as a reflection in a mirror that was being installed in the spectrograph.
Credit:
Dan Long (Apache Point Observatory).
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About SDSS-III
Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating
Institutions, the National Science Foundation, and the U.S. Department of Energy Office of Science.
The SDSS-III web site is http://www.sdss3.org .
SDSS-III is managed by the Astrophysical Research Consortium for the Participating Institutions
of the SDSS-III Collaboration including the University of Arizona, the Brazilian Participation Group,
Brookhaven National Laboratory, Carnegie Mellon University, University of Florida, the French
Participation Group, the German Participation Group, Harvard University, the Instituto de Astrofisica
de Canarias, the Michigan State/Notre Dame/JINA Participation Group, Johns Hopkins University, Lawrence
Berkeley National Laboratory, Max Planck Institute for Astrophysics, Max Planck Institute for
Extraterrestrial Physics, New Mexico State University, New York University, Ohio State University,
Pennsylvania State University, University of Portsmouth, Princeton University, the Spanish Participation
Group, University of Tokyo, University of Utah, Vanderbilt University, University of Virginia, University
of Washington, and Yale University.
Contacts:
- Steven R. Majewski, University of Virginia, srm4n@virginia.edu, 1-434-924-4893
- Jon Holtzman, New Mexico State University, holtz@nmsu.edu, 1-575-646-8181
- Gail Zasowski, The Ohio State University, gail.zasowski@gmail.com, 1-614-292-3099
- John Wilson, University of Virginia, jcw6z@virginia.edu, 434-924-4907
- Michael Wood-Vasey, SDSS-III Spokesperson, University of Pittsburgh, wmwv@pitt.edu, 1-412-624-2751
- Jordan Raddick, SDSS-III Public Information Officer, Johns Hopkins University, raddick@jhu.edu, 1-410-516-8889
