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	Backyard Astronomers Catch Star in Outburst By Daniel Eugene Brannen Jr. Special to SPACE.com posted: 07:06 am ET 11 October 2000

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Some amateur stargazers dream of working with one of NASAs "Great Telescopes." Others do it.

SS Cyg's September Outburst

Amateur astronomers worldwide teamed up recently with two orbiting telescopes to observe SS Cygni, a violent double star system in the constellation Cygnus that brightens roughly every 50 days during an explosive outburst. Click to watch the September outburst .

Amateur astronomers worldwide teamed up last month with NASAs Chandra X-ray Observatory and the now defunct Extreme Ultraviolet Explorer (EUVE) to observe SS Cygni, a double star in the constellation Cygnus that brightens seven times each year during explosive outbursts. After keeping a vigil for weeks with their backyard telescopes, the amateurs saw the latest outburst begin and alerted controllers to commence observations with the orbiting telescopes.

Team works

Such a collaboration, well established in variable star research, is the elegant solution to a simple problem. Professional astronomers study SS Cygni and other dwarf novae to learn about the physics of stellar outbursts. SS Cygnis activity, however, occurs irregularly -- usually every 45 to 60 days -- and observing time on Chandra requires advance arrangements.

"Chandra cannot sit on a target for two weeks waiting for an outburst," says Dr. Christopher Mauche, the principal investigator for Chandra operations. The same holds true for ground-based professional telescopes, where observation time is scarce.

The solution is a team effort between the technical staff at the American Association of Variable Star Observers (AAVSO) -- amateur observers in the field -- and the professionals who operate Chandra and other orbiting telescopes.

"We have light curves for SS Cygni going back 100 years," says Dr. Janet Mattei, Director of AAVSO. "Our staff does a lot of work predicting when SS Cygni might go off based on this historical data."

In this case, AAVSO predicted SS Cygni might have an outburst in the latter half of August, weeks before the star eventually went off. This quiet period, called quiescence, was substantially longer than normal.

"That made constant monitoring all the more critical," explains Dr. Mattei. A long quiescence usually means the outburst will reach maximum quickly. "It was essential that our observers catch SS Cygni right at the beginning if Chandra was going to get a look at the outburst during maximum, as desired."

Global coverage

Amateurs rose to the challenge. Observing from cities and dark sky sites around the world, they provided optical coverage through the night of Saturday September 9, when SS Cygni finally brightened from its quiescent 12th magnitude to below 9th magnitude, making it visible in binoculars.

Observing from his backyard in Espoo, Finland, Tino Kinnunen saw SS Cygni before and after it broke the 11th-magnitude barrier, the hallmark of an outburst. Kinnunen made 10 observations in seven hours that night.

"Above 11.0, it seemed to be picking up speed," said Kinnunen, who looked one final time when the star was around 10.6.

An hour and a half later and a continent away, Tom Burrows focused his 6-inch (152-millimeter) telescope on SS Cygni from his backyard in Petaluma, California.

"I caught it at magnitude 10.4, just after sunset," said Burrows. "I checked it twice more the same night, during which it rose slightly more than half a magnitude. The outburst was obvious."

As the thick of night left California and moved out to Hawaii, Mike Linnolt listened to a hunch that told him to check the star before going to bed.

"I almost did not catch it going up this time," admits Linnolt, who observes from his apartment in Honolulu. "I had been out late and was a bit tired, but just had this funny feeling I better take a quick look. Since it was too high to see from my apartment, I carried the optical tube of my 20-centimeter (7.9-inch) scope up on the roof of my apartment building and propped it against my legs for support to do the observation."

Before turning in, Linnolt caught SS Cygni at magnitude 9.7. The outburst was well underway and headed for maximum.

Anatomy of an outburst

On Sunday morning, Dr. Mattei analyzed the data from the previous nights observations and called Dr. Mauche to say it was time to turn on Chandra and EUVE. Beginning on September 12, Chandra shared a few bars of EUVEs swan song in Cygnus as they made x-ray and extreme-ultraviolet observations, respectively, for two days while amateurs continued to monitor SS Cygnis visible light.

Professional astronomers now plan to use the multi-wavelength observations to test their theories of how cataclysmic variable stars work.

History and Future of AAVSO/Spacecraft Collaborations

AAVSOs first spacecraft collaboration also involved SS Cygni, albeit accidentally. In November 1974, astronomers at the Massachusetts Institute of Technology used an x-ray detector aboard a sounding rocket to observe six different stars. By happenstance, the astronomers noticed an x-ray source near SS Cygni, an unintended target of their research. By comparing this data with visual observations made by AAVSO observers, the astronomers discovered that the star was at maximum outburst during the x-ray emissions. That discovery paved the way for collaborations with 24 spacecraft since 1974.

Multi-wavelength observations of cataclysmic variables such as SS Cygni have comprised a large percentage of these collaborations, and there are more on the horizon. Dr. Mauche hopes to take another look at SS Cygni with Chandra when the star has its next outburst, probably in late October or early November. Dr. Paula Szkody at the University of Washington wants to use Chandra to observe another cataclysmic variable, U Geminorum, during quiescence. She plans to have AAVSO members monitor the star and alert her when an outburst begins. Then she can schedule an observing run for a few weeks later, confident that the outburst will have ended by then.

Astronomers already know SS Cygni is a binary star made up of a cool red dwarf and a heavier white dwarf orbiting around a common center of gravity 100,000 miles (160,930 kilometers) apart every six and a half hours. During this furious dance, the white dwarf steals matter from the red dwarf, collecting it in a halo-shaped accretion disk. According to current theory, an outburst occurs when an instability causes matter to fall from the accretion disk onto the surface of the white dwarf through the boundary layer between them.

Chandras x-ray observations will help astronomers study radiation from the boundary layer, revealing the physics at work there. Data collected by AAVSO and EUVE will test the outburst model. Optical light observed by the amateurs comes from the outer edge of the accretion disk while extreme-ultraviolet energy comes from the boundary layer.

"By measuring the delay between the optical and extreme-ultraviolet energy, we gain information on how fast it takes the outburst to travel from where the instability started to the inner edge of the disk," explains Dr. John Cannizzo of NASA's Goddard Space Flight Center. "We also can make inferences about the physical mechanism that produces the outburst."

For the love of it

As professional telescopes continue growing to astounding sizes, this science would be nearly impossible without the amateur observers who have turned their favorite hobby and small telescopes into a valuable source of data.

"By far the best constraints for my kind of theoretical work comes from the amateurs who keep track of the bright dwarf novae like SS Cygni," exclaims Cannizzo.

Mauche joins this chorus of professionals who praise the variable-star research done by amateur astronomers.

"The real great thing about AAVSO is they have people all over the world. Someone, somewhere is going to have good weather and the right equipment to catch an outburst. It really comes down to some guy in his backyard with a 10-inch (254-millimeter) telescope putting everything in motion."

The amateurs, meanwhile, get to relish not only the value of their contributions, but also the sheer excitement of discovery.

"Most amateur astronomers observe the sky to see what it looks like," says Burrows. "But for a few moments, before we trot into the house and phone things in, variable star observers know things that no one else knows."

Asked to convey the feeling of that moment, amateur Sergio Foglia from Italy responds simply, "Eureka!"