SDSS-II supernova survey explodes with new findings (Forwarded)

Sloan Digital Sky Survey

CONTACTS:
Joshua Frieman
Fermi National Accelerator Laboratory (Fermilab)
At Fermilab: 630-840-2226; University of Chicago: 773-702-7971

David Weinberg
Scientific Spokesperson, The Sloan Digital Sky Survey
At AAS: 614-406-6243

Gary S. Ruderman
Public Information Officer, The Sloan Digital Sky Survey
312-320-4794

January 12, 2006

SDSS-II SUPERNOVA SURVEY EXPLODES WITH NEW FINDINGS

WASHINGTON DC -- The population of supernovae -- exploding stars in
distant galaxies -- has exploded here on Earth with an unprecedented
number of new discoveries logged in just 90 days by the Sloan Digital Sky
Survey (SDSS-II).

The Sloan Supernova Survey today reported the discovery of 139 new Type Ia
supernovae during its first campaign last fall.

These supernovae will be used to provide more precise constraints on the
nature of the mysterious Dark Energy that is causing the expansion of the
Universe to speed up. They will also yield greater understanding of
supernovae as standard distance signposts (aka standard candles or
standard light bulbs) in the Universe.

"Finding so many supernovae in such a short time is unprecedented, because
the SDSS probes a larger volume of space than previous surveys," explained
supernova team co-leader Joshua Frieman of the Fermi National Accelerator
Laboratory (Fermilab) and the University of Chicago. The results were made
public during a session on Supernovae and Cosmology at the American
Astronomical Society's winter meeting in Washington, DC.

To find supernovae, the team used the dedicated SDSS-II 2.5-meter
telescope at the Apache Point Observatory in New Mexico. Its 120-megapixel
CCD camera is used to scan the same part of the sky roughly every other
night over a three-month period, searching for supernovae that explode in
any of the three million galaxies it sees. Comparing images taken on
different nights, astronomers can look for objects that have brightened
over time -- potential supernovae. Shortly after it explodes, a supernova
becomes as bright as an entire galaxy, so it can be seen across vast
cosmic distances.

"An advantage of the SDSS is that it carries out nearly simultaneous
imaging in five different portions of the optical spectrum, providing
measurements of the colors as well as the brightness of objects,"
explained Masao Sako of Stanford University. Using these colors, Sako and
other members of the SDSS-II supernova team were able to zero in with very
high efficiency on the prized Type Ia supernovae, the most precise
standard candles.

The most promising Type Ia candidates were targeted for follow-up
spectroscopy on a variety of other telescopes, including the Astrophysical
Research Consortium's 3.5-meter telescope, the Hobby-Eberly 9.2-meter
telescope in Texas, the William Herschel 4.2-meter telescope in the Canary
Islands, Japan's Subaru 8.2-meter telescope, Keck 10-meter telescope in
Hawaii and the MDM Hiltner 2.4-meter telescope in Arizona.

"Follow up observations that measure the spectrum of the supernova are
critical," explained team member John Marriner of Fermilab. "First, they
confirm that the candidate is a Type Ia rather than some other kind of
supernova, and second, they determine the velocity at which it is receding
from the Earth." That recession velocity is caused by the expansion of the
Universe; by combining the brightnesses and recession velocities of large
numbers of supernovae, astronomers can unravel the history of the cosmic
expansion rate.

Since supernovae are bright only for a few weeks, the candidates must be
identified quickly so that their spectra can be measured before they fade.
A cluster of 10 dual-processor computers at the observatory automatically
processes the data and looks for differences between the images just taken
and those of the same part of the sky in previous years.

"A full night of data collection with the telescope yields about 2,400
images, each one roughly equivalent to the image in a four-megapixel
digital camera. We process these images with our computers in about 20
hours," explained supernova researcher Richard Kessler of the University
of Chicago. "This accumulation of 70 gigabytes of images each night is
equal to more than 100 CDs or 15 DVDs."

The new supernova sample also bridges the gap between the nearby
supernovae found in local surveys and the very distant objects found by
deeper surveys of much smaller areas. "The combination of a 2.5-meter
aperture and a very large field of view makes the SDSS telescope ideal for
finding intermediate distance supernovae, about 1 to 3 billion light years
from Earth," explained Jon Holtzman of New Mexico State University. "Only
a handful of supernovae at these distances had been found previously."

"All of the well-known results on the accelerating universe have so far
come from comparing nearby supernovae to distant supernovae that were
discovered and measured in different kinds of surveys," added Frieman.
"The SDSS-II survey fills in the missing rungs on the ladder."

The race to improve the quality of supernova samples over a range of
distances is heating up.

"The Sloan Supernova Legacy Survey and the ESSENCE survey are compiling
more distant samples that will include hundreds of supernovae by the time
they each finish a few years from now," noted Craig Hogan of the
University of Washington. "Combining the SDSS results with these deeper
surveys will probe the cosmic expansion and the nature of the dark energy
with greater precision." (ESSENCE is a five-year supernova survey designed
to constrain the physics of Dark Energy,
http://www.ctio.noao.edu/wproject)

The SDSS researchers are also looking forward to some surprises in the
"astronomical zoo."

"We focused on the type Ia supernovae this season, because of the exciting
cosmology applications, but the SDSS gives us a unique tool to study
unusual supernova types," noted Stanford University's Roger Romani. "We
have shown that we can sift through hundreds of new supernovae to select
the rare gems. With a survey volume this large, these rarities turn up
frequently enough to allow serious investigation of their place in the
astronomical zoo."

SUPERNOVAE BACKGROUND

Type Ia Supernovae are formed when white dwarf stars -- the remnants of
stars similar to our Sun -- collapse inward and blow up like an atomic
bomb in brief but intense bursts of energy. The white dwarf accumulates
gas from a companion star until it explodes, spewing gas and particles of
iron, nickel and cobalt. The brightness of the Type Ia light peaks about
three weeks after the explosion and declines over a period of months.

In the early 1990's, astronomers found that type Ia supernovae could be
used to study cosmological distances because they appear to be accurate
standard candles. In 1998, two research groups studying distant type Ia
supernovae found that they were fainter than would be expected if the
expansion of the Universe were slowing down due to the attractive pull of
gravity. Instead, the evidence, which has since been confirmed by other
cosmological observations, pointed to a speed-up of the Universe that
began a few billion years ago. The cause of this acceleration is thought
to be a bizarre form of energy, dubbed dark energy, which permeates the
Universe and acts as a source of gravitational repulsion.

Information about the newly discovered SDSS-II supernovae has been
distributed to the astronomical community via the International
Astronomical Union circulars and the Central Bureau for Electronic
Telegrams. These listings of supernova discovery dates, positions,
magnitudes, and list of co-authors helps the community perform follow-up
research. The public listing of confirmed supernovae is at
http://sdssdp47.fnal.gov/sdsssn/snlist.php

The Sloan Supernova Survey is one of three research and discovery
components of The Sloan Digital Sky Survey (II), which will run through
mid-2008.

AUTHORS:

* J. Barentine, Apache Point Observatory (APO)
* B. Bassett, University of Portsmouth (UP)
* A. Becker, University of Washington
* R. Bender, University of Munich (UM)
* M. Bremer, University of Bristol
* H. Brewington, APO
* F. DeJongh, Fermilab
* J. Dembicky, APO
* D. L. DePoy, Ohio State University (OSU)
* B. Dilday, University of Chicago (UC)
* M. Doi, University of Tokyo (Tokyo)
* E. Elson, South African Astronomical Observatory (SAAO)
* J. Frieman, Fermilab and UC
* P. Garnavich, University of Notre Dame
* M. Harvanek, APO
* T. Gueth and J. Holtzman, New Mexico State University
* U. Hopp, UM
* W. Kollatschny, Goettingen University
* K. Konishi, Tokyo
* J. Krzesinski, APO
* H. Lampeitl, Space Telescope Science Institute (STScI)
* R. Kessler, UC
* B. Ketzeback, D. Long, O. Malanushenko, V. Malanushenko, APO
* J. Marriner, Fermilab
* J. L. Marshall, OSU
* R. McMillan, APO
* G. Miknaitis, Fermilab
* T. Morokuma, Tokyo
* R. Nichol, UP
* K. Pan, APO
* J.L. Prieto, OSU
* M. Richmond, Rochester Institute of Technology
* A. Riess, STScI
* R. Romani and M. Sako, Stanford University (SU)
* D. Schneider, Penn State University
* M. Smith, UP
* S. Snedden, APO
* M. Subbarao, UC and Adler Planetarium
* N. Takanashi and K. Tokita, Tokyo
* K. van der Heyden, SAAO
* J. C. Wheeler, University of Texas
* N. Yasuda, Tokyo

IMAGE CAPTION:
[(left) http://www.sdss.org/news/releases/20060112.SN.1.png (80KB)
(Right) http://www.sdss.org/news/releases/20060112.SN.2.png (121KB)]
SDSS-II images of a Type Ia supernova on the rise (left) and near maximum
light (right).
CREDIT - SDSS-II Collaboration