August 24, 2009
Catalina Real-Time Transient Survey
The Catalina Sky Survey detects potentially hazardous asteroids and comets. Now a spin-off survey is finding a windfall of "optical transients" in the same data.
Astronomers have been mining a mother lode of astronomical data from the University of Arizona's Catalina Sky Survey and finding more "optical transients" than they can characterize during the past 17 months.They have found more than 700 unique "optical transients," or objects that change brightness on time scales of minutes to years.
They've also found 177 supernovae. That's more than dedicated supernova surveys have turned up during that time.
Their discoveries include the most energetic supernova ever seen, and a nearby stellar explosion in the Antennae galaxy that is helping astronomers refine the cosmic distance scale. Unlike most dedicated supernova surveys, Catalina Sky Survey telescopes cover the entire sky each month, allowing the team to record supernovae in dim galaxies where others weren't looking.
The bonanza of transient optical objects detected in the Catalina Sky Survey data also includes:
* 185 cataclysmic variable stars, which is about three out of every four such objects discovered over the same time span and more than the Sloan Digital Sky Survey found in six years. This result suggests that cataclysmic variables are more common than previously thought.
* 32 blazars, or beamed active galactic nuclei. These very compact and highly variable energy sources are among the most violent phenomena in the universe.
* About 30 stellar flares, which are large explosions in stellar atmospheres.
* About 100 other highly erratic light sources that include active galactic nuclei, high proper motion stars and sources that remain unknown.
Capturing such ephemeral astronomical events is not what the Catalina Sky Survey is primarily about. NASA funds the Catalina Sky Survey, or CSS, to search for potentially hazardous, Earth-orbit crossing asteroids and comets, also called Near-Earth objects, or NEOs.
The CSS is the most successful NEO survey that exists. CSS observers have found about 70 percent of all NEOs discovered over the past three-and-a-half years.
Two years ago, Catalina Sky Survey director Ed Beshore and co-investigator Steve Larson of the UA's Lunar and Planetary Laboratory began collaborating with scientists at the California Institute of Technology's Center for Advanced Computing Research on a pilot project to mine the CSS data for optical transients.
CSS is a relatively small-budget operation. Six observers use the UA's 1.5 meter, or 60-inch reflector telescope at Steward Observatory's Mount Lemmon site and the 0.7-meter, or 28-inch Schmidt telescope near Mount Bigelow in the Santa Catalina Mountains north of Tucson. Two observers use Australian National University's 0.5-meter, or 20-inch Uppsala Schmidt telescope at Siding Spring, New South Wales, Australia. Each telescope takes about 20 gigabytes of data each night.
Caltech astronomer Andrew Drake tapped real-time data from the 28-inch Schmidt telescope on Mount Bigelow for the pilot project. Drake and his colleagues at Caltech observed many of the new CSS discoveries using some of the most powerful telescopes in the world, including the Hale Telescope at Mount Palomar, the Keck Telescope on Mauna Kea and the Gemini Telescope in Chile
Last year, the Caltech team wrote a National Science Foundation proposal to expand what's called the Catalina Real-Time Transient Survey, or CRTS, into a true, fully open synoptic sky survey.
Thanks to the $890,000 NSF grant awarded this month, the CRTS team soon will construct a Web site that will make roughly 10 terabytes of data taken by the Catalina Sky Survey over the past five years "“- as well all new CSS data that continues to stream in -- available over the Internet to astronomers worldwide, professional and amateur.
The Catalina Real-Time Transient Survey will be the first and only fully public synoptic sky survey, team members say. It's a bargain-rate boon to astronomers who are trying to figure out how to manage enormous data streams to be delivered by future synoptic sky survey telescopes, such as Pan-STARRS and the LSST, they add.
"The grant will allow our Caltech colleagues to expand our project to get real-time data from our two other telescopes "“ the 1.5 meter Mount Lemmon telescope and the Siding Spring telescope in Australia "“ and buy computers and storage equipment that will allow them to put all this data online for anybody in the world to use," Larson said.
Researchers will be able to compare real-time CSS images to any image in the 5-year CSS archive, thanks to a fortuitous decision early on.
"Fortunately, we decided to divide the sky into a grid and basically shoot and reshoot the same defined patches of sky within that grid," Beshore said. "That's a big help when it comes to comparing what a specific patch of sky looked like earlier and what it looks like now."
The emergence of CRTS illustrates an important new trend in astronomical research "“ the search for objects that appear, disappear and even move, Beshore said. "Objects can change on time scales of minutes, hours and weeks, not just years."
"We've seen a star dim in images taken only 10 minutes apart, for example," Larson said.
The CSS team can co-add all the images taken at a specific place on the sky and get a very deep sky image showing very faint objects, objects down to the 21st magnitude, Larson added.
Former team member Eric Christensen produced the CSS team's first catalog of deep-sky images in this way. The CSS team is contributing its cataloged images to the CRTS.
Releasing data over the Internet in real time rather than keeping it proprietary is another striking trend in astronomy, and a necessary one, Larson and Beshore say. Observers see many more objects in their data than they have time to follow up.
"We just crank out the data so amateurs and professionals alike can figure out what they can do with it," Beshore said.
The optical transient search is a valuable spin-off astronomy project born from the Catalina Sky Survey's search for near-Earth asteroids and comets.
But NASA funders can rest assured that Catalina Sky Survey observers remain focused on their primary mission:
Last year CSS tallied 565 NEO discoveries, breaking its own record of 460 NEO discoveries the previous year. Also last year, a CSS team member made history when he spotted the small asteroid 2008 TC3 hours before it became a brilliant fireball over Sudan.
It was the first time scientists discovered an asteroid before it reached Earth and predicted when and where the impact would be. U.S. and African students and researchers recovered more than eight pounds of meteorites from the fall.
By Lori Stiles, University of Arizona
Image 1: The arrow points to a supernova discovered in a nearby pair of colliding galaxies called the Antennae. The supernova was discovered in the Catalina Real-Time Transient Survey that uses data collected by UA Lunar and Planetary Laboratory observers using telescopes in the Santa Catalina Mountains north of Tucson. (Photo: Robert Gendler)
Image 2: Now you see it, now you don't, now you do. This CRTS image shows how quickly astrophysical objects can disappear and reappear. In this image, the box surrounds a so-called polar cataclysmic variable star that fades by 7,500 percent in about 10 minutes, then recovers completely 10 minutes later. (Catalina Real-Time Transient Survey)
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