Nova outburst in Cygnus
BY MARK ARMSTRONG
ASTRONOMY NOW
Posted: March 17, 2008

A nova has recently erupted in the constellation of Cygnus, the Swan and is easily visible in small telescopes although sadly not with the naked-eye. Nova Cygni 2008 was discovered on 7 March by Japanese amateur Hiroshi Kaneda, who used a digital camera with a 105mm f/2.5 lens. Independent discoveries quickly followed from the same night by Martin Nicholson of Daventry, England and Zhang-wei Jin and Xing Gao, at Xingming Observatory, Mount Nanshan, China, as part of their nova survey. Interestingly it was this set-up that discovered the recent comet C/2008 C1 (Chen-Gao).

Nova Cyg 2008. This image was taken by M. P. Mobberley on 9 March 2008, 9.480 UT (11:30-11:32 UT); remotely imaged using GRAS (New Mexico) GRAS-005 Takahashi Epsilon 250 f/3.4 (850mm fl) + SBIG ST 10MXE, Bin 2x2 x 80% 120s.

The nova was discovered around magnitude +8 with Kaneda noting that nothing was visible on a previous image he took on 18 February, which showed stars down to magnitude +10.5. The nova has undergone a slow fade to currently be approximately magnitude +9 on 17 March, so it should be visible in large binoculars (15 x 80s).

Classical novae are a class of cataclysmic variables with the explosive mechanism thought to be the outburst of material on the surface of a very dense star called a white dwarf in a close binary system with a main sequence (Sun-like) star. The main sequence star is losing material to the white dwarf, resulting in the material forming a disc around the dwarf. Over periods of between 10-100,000 years enough material has spiraled down on to its surface to trigger a thermonuclear explosion. This massive event causes a rise in brightness of some 7 to 16 magnitudes, but does not result in the complete destruction of the star, unlike a supernova.

Novae are unpredictable events with perhaps as many as 40 outbursts per year in a galaxy the size of our Milky Way. Many go undiscovered as so-called ‘fast novae’ can rise quickly to prominence only to become a run-of-the-mill speck of light before astronomers can spot them. Amateur astronomers do conduct organized searches and can be spectacularly successful such as the late, great George Alcock (see April 2008 issue of Astronomy Now) and Bill Lillier in South America.

If you want to catch a glimpse of this latest outburst you should point your telescope some six degrees east-north-east of the celebrated double star Albireo (beta Cygni). The precise position is RA: 19h 58m 33s.38, Dec: +29° 52’ 06”.5. The only snag is that Cygnus is a summer constellation and observers will need to wait to around 3am GMT for the nova to rise out of the eastern murk. Keen observers might like to try to follow the behaviour of the nova over the next few months as this can often be unpredictable with sudden increases in brightness possible, arresting a smooth fade.   

The location of Nova Cygni is identified by the orange circle near Albireo. Graphic by Greg Smye-Rumsby.