A Star Erupts

A nova is shining in the constellation Eridanus. Although not bright enough for naked-eye viewing, it’s an interesting object. It was discovered on Nov. 25 by an astronomer named Koichi Itagaki of Yamagata, Japan.

[Patrick Wiggins’ view of the nova, arrowed, with two reference stars circled. Two months ago the star that was to go nova was dimmer than the reference stars]

The word nova derives from Latin meaning new star, but technically it isn’t new. The Hubble Space Telescope Guide Star Catalog designates the star as GSC 5325:1837. What’s new is that it brightened so much that it went from impossible to see without a good telescope to visible through binoculars if you knew where to look.

A nova is the sudden brightening of a star, as when one star in a binary system strips off material from another.

Patrick Wiggins, NASA solar system ambassador to Utah, pointed out that nova doesn’t mean an exploding star; that is a supernova.

“When a supernova occurs it essentially blows a star to pieces,” he said. A nova is a tremendous brightening, followed by a fading, an event that does not destroy the star. Some novae are pulsating types, meaning the event happens repeatedly.

According to an alert by Roger W. Sinnott of Sky and Telescope Magazine, word of the nova discovery was relayed by the Central Bureau for Astronomical Telegrams, based at the Smithsonian Astrophysical Observatory in Cambridge, Mass. Sinnott added, “Itagaki was using an 0.21-meter (8.3-inch) patrol camera, but within 15 minutes he secured a confirming image with an 0.60-meter reflector.”

He wrote that the magazine’s senior editor, Alan MacRoberts, sent an e-mail late on Nov. 28 saying, “Just spotted the nova in my 10X50 binocs on their wooden shoulder frame. Barely visible through the bright moonlight at about 8.4 mag.” That magnitude is well below the minimum for visual notice, which is about 6, but far brighter than the star had been.

On Nov. 30 (Dec. 1 Universal Tine), I spent four frigid hours in our front yard trying to photograph the nova. I attempted star-hopping the telescope from the Orion Nebula, to the furiously bright Rigel, to the nova, but never managed it. As I noted that night, “… by the end of the session I had the weirdest distortion imaginable. Finally I realized that I had been frosted again.”

The year’s observing began with frost covering my telescope and my last attempt of the 2009 ended the same way.

Meanwhile Wiggins had better luck with his scope, which is well protected from frost. On Nov. 30 (Universal Time), he began photographing the nova and recording its brightness. Without getting technical, I should say that the larger the magnitude number, the dimmer the star.

He found these changes, all in images taken through a red filter:

Nov. 30, magnitude 9; Dec. 1, magnitude 9.15; Dec. 3, 9.25; Dec. 4, magnitude 9.35; Dec. 10, magnitude 9.9; Dec. 11, a little brighter at magnitude 9.83; Dec. 15, magnitude 10.25; Dec. 18, magnitude 10.3; Dec. 19, magnitude 10.25.

[Chart by Patrick Wiggins showing the nova’s decrease in brightness, indicated by red crosses and lines, compared with brightness of two companion stars, shown by blue line. Units are hours]

“Tonight the magnitude is right about 10.25,” he said by telephone as he ended that run of photos. “It has increased ever so slightly from last night.” To reduce distortions from an unsteady atmosphere, Wiggins has his computer average the brightness of 50 two-second photos of the nova, every night that he measures it. The program calculates how bright the target star is by comparing it to a nearby star of known magnitude.

After the photos are taken the software examines the images, determining star magnitudes. “It takes maybe half a second to measure each one.”

By now the nova is only one-third as bright as it was three weeks ago, but it remains more intense than before the eruption. Novas tend to appear suddenly and trail off gradually, he said.

Recording astronomical data is rewarding, according to Wiggins. Even though this nova isn’t an impressive one, it is yielding scientific information that can help astronomers better understand the demise of stars. That’s why he likes this kind of project better than astrophotography.

“We look at [astronomical] pictures taken a hundred years ago and say, ‘Is that crude or what?'” he said. That seems likely to happen in the future too. But he believes data recorded today still could be valuable in a century.

[On left, a digital sky survey image from before the nova; on right, the same region as photographed by Wiggins during the nova]

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