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Amateur and Professional Astronomers Team Up for Chandra Observations of SS Cygni

September 14, 2000 ::

Chandra X-Ray Observatory

September 14, 2000 :: Triggered by alerts from amateur astronomers worldwide NASA's Chandra X-Ray Observatory is observing the outburst of the brightest northern dwarf nova SS Cygni. The amateur stargazers provided Chandra scientists with a crucial early-warning of this outburst by calling-in their visual observations of SS Cygni as soon as they saw the star brightening. With the cooperation of hundreds of amateur astronomers, the Chandra observatory is monitoring SS Cygni's X-ray emission during its maximum brightness.

The amateur's observations of this star are done with backyard optical telescopes. The data they provide about the star's optical brightening, combined with the X-ray spectra gathered by the Chandra satellite, will reveal the nature of the flow of gas from a small red star onto its shrunken, dying companion.

Dr. Janet A. Mattei, Director of the American Association of Variable Star Observers (AAVSO)--a non-profit organization made up of mostly amateur astronomers -- and her technical staff are coordinating the collection of optical observations of SS Cygni and communicating them to Dr. Chistopher Mauche at Lawrence Livermore National Observatory, CA who is the Principal Investigator of Chandra observations.

"For years, amateur astronomers have informed professionals of bursting star systems and other cosmic events" said Mattei. "The cooperation between an organized group of dedicated amateur astronomers, and the professional astronomers who need these observations, is now quite finely tuned. When scientists are in need of ground-based observations to follow simultaneous satellite observations, they know that this worldwide network of amateurs can be depended upon for fast, efficient, and reliable results."

Figure 1. Light curve of SS CYG comprised of all observations received for SS CYG from Jan 15 - Sep 13. (Julian Date 2451559 - 2452451801)
Click to enlarge.

The dwarf nova, SS Cygni, is a type of star known as a cataclysmic variable. SS Cygni is a close binary star system in the constellation of Cygnus (The Swan) that contains a red dwarf star and a white dwarf. A red dwarf is a star a little cooler and smaller than the Sun. The white dwarf was once as large as the Sun but subsequently ran out of fuel, blew its outer shell into space, and collapsed to form a white-hot ember, the size of Earth. The dense white dwarf, with its strong gravitational potential, pulls a stream of gas off of its companion star. This transferred gas collects in a disk, called an accretion disk, around the white dwarf.

The dramatic brightening by many orders of magnitude in this system is the result of an instability in the disk, which forces the disk material to drain down onto the surface of the white dwarf. This causes a titanic energy release equivalent to that of billions of atomic bombs exploding every second. Such stellar explosions, which often occur without warning and rarely last more than one or two weeks, serve as floodlights that brighten a dim star system for scientists to study. Figure 1 is a light curve (graph of light variation) showing the behavior of SS Cyg from January 2000 to-date. Each dot represents one optical observation.

The start of the SS Cygni outburst was discovered in its very early stage over the weekend by tens of amateur astronomers who have been "keeping a vigil" to "catch" the outburst. It was then confirmed by other amateurs, many of whom are members of the AAVSO. They e-mailed or phoned-in their observations to the AAVSO. Dr. Mattei communicated this information to Dr. Mauche and advised him to submit the request to start the X-ray observations. Within hours of Dr. Mauche's request on a Sunday, he was speaking with Dr. Fred Seward and Dr. Pat Slane of the Chandra team on the specifics of the requested observations. Thanks to their and other Chandra team's efforts, Chandra observations began on Sept. 12.7 UT and will continue until Sept. 14.5 (Sept 12.7 UT is Sept 12, 16:48 UT or Sept. 12, 12:48 EDT or in Julian Date - 2451800.2).

Dr. Mauche also spoke with Marty Eckert, the EUVE Science Planner, on Sunday to arrange for simultaneous observations of SS Cygni with NASA's EUVE satellite. EUVE measures the brightness and spectra in the extreme ultraviolet, providing unique information about the very short (10 sec) quasi-period oscillations that appear only during outburst in SS Cygni.

This is a wonderful collaboration of amateur and professional astronomers and NASA's pioneering satellites.

The AAVSO was founded in 1911 at Harvard College Observatory to coordinate variable star observations made largely by amateur astronomers and became an independent, non-profit organization in 1954. Today, the AAVSO has members in over 40 countries and maintains the world's largest computer- readable variable star data archive, with nearly 10 million observations, and growing by almost half a million yearly. The AAVSO is headquartered in Cambridge, Massachusetts.

For more information, refer to the AAVSO website at http://www.aavso.org.

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