"The Strangest Star We Have Ever Observed"
|
|
EL SEGUNDO, Calif. (5/26/03) -- "The strangest star we have ever observed." That's how a team of astronomers in the remote sensing department at The Aerospace Corporation and their colleagues describe their infrared observations of V838 Monocerotis.
"The temperature dropped from around 6000 K to around 2000 K in about a year," said Dr. David K. Lynch, an astronomer at Aerospace and team leader. "Stars just don't do that. It appears that V838 Mon may represent a new class of stars, or at least a very rare event in the life of some stars."
The team's observations are being presented today at the American Astronomical Society meeting in Nashville, Tennessee, by Catherine C. Venturini, a physicist at Aerospace, in a paper titled "Dramatic Changes in the Infrared Spectrum of V838 Monocerotis." Co-authors besides Lynch and Venturini are Dr. Richard J. Rudy, Dr. Ray W. Russell, Steve Mazuk, and Dr. William L. Dimpfl (The Aerospace Corporation); Dr. Michael Sitko (University of Cincinnati); Dr. Richard. C. Puetter (University of California, San Diego); Dr. Lawrence S. Bernstein (Spectral Sciences, Inc., Burlington, Mass.); and Raleigh B. Perry (NASA Langley Research Center).
A few days after discovery of the star's outburst in January 2002, observing teams at two observatories obtained infrared spectra. One team used NASA's 3-meter (120-inch) Infrared Telescope Facility on Mauna Kea, Hawaii, and almost simultaneously the other team worked with the University of California's 3-meter Lick Observatory telescope. Using two instruments made by The Aerospace Corporation, the Broadband Array Spectrograph System, BASS 3-14 micrometers, and the Near Infrared Imaging Spectrograph, NIRIS 0.8-2.5 micrometers, the astronomers saw the star's temperature and spectrum change like no other star before.
"Shortly after its outburst it looked like a normal nova. But when we measured it again about a year later, it had turned a lot colder, maybe as cool as 2000 K, with an immense shell that was even cooler (800 K)," Venturini said. "There were molecular features everywhere: water (H 2 O), carbon monoxide (CO), hydroxyl radical (OH), hydrogen sulfide (H 2 S) and mercapto radical (SH), and aluminum oxide (AlO). Also, silicate dust condensed in the shell around the star, much of it like the rock in Earth's mantle. The result is of special interest because it represents some of the first observations of a new kind of star, or perhaps an unusually rapid and violent stage in the star's evolution," she explained.
During this time, many other astronomers have been watching V838 Mon. "Everyone with a telescope was making measurements of V838 Mon. And every measurement was a new discovery. It is the talk of astronomy," Lynch said.
In the months following the outburst, NASA began using the Hubble Space Telescope to monitor the star. They discovered a "light echo" illuminating the material around it that had come off during previous ejection events. The light echo sends a reflection of the material to Earth. Because the light does not take a direct path, its arrival is delayed, like an echo.
"Like many other groups, we will be monitoring V838 as long as it is bright enough to measure," Lynch said. He pointed out that the star is expected to fade during the next few years, returning to its former state as "just another ho-hum star in our galaxy. But until then, V838 Mon will probably have many more surprises for us," he predicted.
The star is called V838 Monocerotis because it is the 838th variable star discovered in the constellation Monocerotis, the unicorn. Its outburst was discovered by Nicholas J. Brown, an amateur astronomer from Quinns Rocks, Western Australia. V838 Mon is about 20,000 light-years from Earth (117 quadrillion miles), which means the explosion actually took place 20,000 years ago in the late Paleolithic period, long before human civilization. The light is just now reaching Earth.
Before January of 2002 the star had been recorded by surveys but was considered unremarkable until it suddenly brightened. Lynch said. V838 became so bright that for a few days it was the brightest star in the Milky Way.
For more information, visit the Hubble Telescope Web site.
