Texas Supernova Search Finds Exploding Stars Fast, Follows Up Fasterwith Giant Telescope (Forwarded)

McDonald Observatory
University of Texas
Fort Davis, Texas

Contact: Rebecca Johnson
ph: 512-475-6763 fax: 512-471-5060

10 January 2007

Texas Supernova Search Finds Exploding Stars Fast, Follows Up Faster with
Giant Telescope

SEATTLE, Wash. -- Robert Quimby, a post-doctoral researcher at The
University of Texas at Austin, is heading up the Texas Supernova Search --
an effort to detect exploding stars of all types in the fastest way
possible after their explosion, to better understand how they explode and
the types of stars they were prior to the explosion. This information will
aid scientists using supernovae in cosmology studies, including the study
of dark energy.

Quimby is explaining his search technique and results in a talk today at
the 207th meeting of the American Astronomical Society in Seattle,
Washington.

The search program uses ROTSE IIIb, a robotic telescope located at The
University of Texas at Austin McDonald Observatory in West Texas. The
telescope is one unit of four placed around the world that make up the
Robotic Optical Transient Search Experiment headquartered at The
University of Michigan. Its primary purpose is to quickly track gamma-ray
bursts. However, 30 per cent of the telescope's observing time is also
available to The University of Texas for other studies like Quimby's Texas
Supernova Search, which uses most of that allocation.

The project has some advantages over other supernova searches. The
telescope has an extremely large field of view -- the width of 3.5 full
Moons on a side (3.4 square degrees). Second, this project looks at the
same patches of sky night after night, Quimby says, explaining that most
other search projects don't work this way. His winter/spring targets
include three grids, which cover the Virgo, Ursa Major, and Coma galaxy
clusters. Together, these fields include hundreds of nearby bright
galaxies, and thousands of nearby dwarf galaxies. Finally, ROTSE IIIb
shares mountaintop space with one of the largest optical telescopes in the
world, the 9.2-meter Hobby-Eberly Telescope (HET). When a supernova is
found by ROTSE, it can immediately be followed up in great detail with
HET.

Since the fall of 2004, the Texas Supernova Search has found about 30
supernovae.

Quimby explains that while "hundreds of supernovae are found every year"
now by various search groups, the idea behind his project is to try to get
the earliest look at new supernovae. In other words, he says, "not to find
the most supernovae, but to find the best supernovae."

He explains that "when a supernova explodes, the material expands and
thins out. When it fans out, you see deeper into the explosion. Most
people studying supernovae are looking fairly deep" into the expanding
debris cloud.

In contrast, "we look early," he says. This enables him to study the
exploded star's outer layers, before the debris cloud has had much time to
expand.

The benefit of catching supernovae as soon as possible after they explode,
Quimby says, is to get information that is only available by studying the
star's outer layers. This includes information about the progenitor star,
and about the explosion itself.

"There are very few examples of supernovae that have been studied in the
first few days," Quimby says -- less than a dozen. His survey recently
discovered one, known as supernova 2006bp. Quimby says the Texas Supernova
Search found 2006bp about two days after it exploded. (It was
independently reported earlier by amateur astronomer Koichi Itagaki of
Yamagata, Japan.)

This early detection is important, because such studies might reveal
differences in supernovae soon after they explode, which at later times
look identical. The great value of supernovae (specifically, type Ia
supernovae) to cosmology research is their uniformity -- astronomers can
count on them to have a certain peak luminosity for a given light curve
shape, which allows them to calculate distance to the supernova (and its
host galaxy) with great confidence. These measurements were integral, for
instance, in the calculations that revealed that the expansion of the
universe is accelerating, and introduced what many call the greatest
enigma in science today -- dark energy.

But what if all supernovae aren't the same? Quimby's search caught one
exploded star that hints of this possibility: supernova 2005hj. Once the
search found this supernova, they began following it as it changed day by
day using the HET. Spectra taken over a period of time showed that the
light output from this supernova changed over time in a way different from
the norm.

"At first, the velocity of the ejecta decreased over time as is typical,"
Quimby says. "But this was followed by about a two-week period of nearly
constant velocities, which is unusual."

Quimby says there are two possible explanations for 2005hj's unusual
behavior. It could be a merger of two white dwarf stars -- the so-called
"double degenerate" model. The second possibility is that it could be a
white dwarf star that tried to explode, but didn't release enough energy.
So it puffed up a bit, then collapsed back onto the star's core,
triggering a second (much larger) explosion. This case is known as a
"pulsating delayed detonation."

The Texas Supernova Search will continue. Quimby hopes to expand the
program to include all four ROTSE telescopes. Besides unit IIIb at
McDonald Observatory, there are ROTSE telescopes in Australia, Turkey, and
Namibia.

The Hobby-Eberly Telescope is a joint project of The University of Texas
at Austin, The Pennsylvania State University, Stanford University,
Ludwig-Maximilians-Universität München and Georg-August-Unversität
Göttingen.

-- END --

Note to Editors: Robert Quimby can be reached in Seattle this week and
thereafter in Austin at 512-471-7460.

IMAGE CAPTIONS:

[Image 1:
http://mcdonaldobservatory.org/news/...age.php?id=98]
Supernova 2006bp was discovered by the Texas Supernova Search within two
days of its explosion. Credit: Robert Quimby, UT-Austin McDonald
Observatory.

[Image 2:
http://mcdonaldobservatory.org/news/...ge.php?id=100]
The Texas Supernova Search is carried out by post-doctoral researcher
Robert Quimby using the ROTSE IIIb telescope at McDonald Observatory.
Credit: Robert Quimby, UT-Austin McDonald Observatory.

[Image 3:
http://mcdonaldobservatory.org/news/...age.php?id=99]
The Robotic Optical Transient Search Experiment has placed telescopes in
four locations on Earth to cover the entire sky in search of gamma-ray
bursts. One of these, ROTSE IIIb, is located at McDonald Observatory. In
addition to its primary mission, the telescope is used for the Texas
Supernova Search. Credit: ROTSE Collaboration.

[Image 4:
http://mcdonaldobservatory.org/news/...age.php?id=36]
The Hobby-Eberly Telescope. Credit: Marty Harris/McDonald Observatory.