Australian Amateur Spots 'Outburst of the Year'

Yesterday, Australian amateur astronomer, Rod Stubbings, sent out notification to several cataclysmic variable email lists that VX Fornax is in outburst. This is one of those objects that effectively hides from astronomers for decades and then suddenly brightens by several magnitudes, prompting amateur and professional astronomers to aim their telescopes and satellites at it while it is showing off for us.

How rare is this? The last time anyone saw VX For in outburst was in 1990. It was discovered by famed nova hunter, William Liller, of Vina del Mar, Chile on October 25th, 1990 at photographic magnitude 12.5. An exposure taken one week prior showed nothing down to blue magnitude 19, so this was a very faint system that suddenly brightened by 7 or 8 magnitudes in the visual bands. Spectra taken later that week indicated it was not a classical nova, but more likely a dwarf nova.

Determining what type of CV this actually was stumped astronomers the first time around, so this eruption is potentially important. Joe Patterson, of the Center for Backyard Astrophysics explains.

"This star zoomed to 12.6 from about 20.5 in 1990, and stayed bright for many weeks (declining at ~0.1 mag/day). The spectra made it pretty clear it was an erupting dwarf nova, and even in 1990 it seemed very, very likely that the star would flash superhumps."

[Superhumps are a characteristic variation in the light curve of SU UMa and WZ Sge type CVs when they have a brighter than normal outburst known as a 'superoutburst'.]

"But I studied it for 7 straight nights at Cerro Tololo, and found only small and apparently aperiodic wiggles in the light curve. Basically a very high-quality nothing. Then my run ended... and I've always wondered what this star is.

Now it's 2009, and we know a lot more about the WZ Sge syndrome among dwarf novae. The most extreme of these stars generally take quite a long time to sprout actual superhumps; WZ Sge itself takes 10 days. So that's a pretty good conjecture - that it's quite extreme even among the WZ Sge class... and that had I taken over that 0.9 m telescope and refused to leave, I would eventually have seen those telltale superhumps.

We don't yet know much about this eruption, but if it's a superoutburst (and odds are decent), then this is the glamor object of the year for dwarf novae."

This is another example of how amateur astronomers can contribute to astronomy. Many of them keep tabs on these obscure objects night after night, for sometimes decades, before anything interesting happens. Professional astronomers can't use valuable telescope time waiting for something to happen, so this area of discovery is left almost entirely to amateurs.

Now all eyes, telescopes and CCDs in the southern hemisphere are pointed at VX For and will be until this eruption fades and the star is a faint, 20th magnitude binary, building up accreted material at a leisurely pace in preparation for the next rare outburst, which may be twenty years from today.

Congratulations to Rod on his detection of this rare cataclysmic variable outburst. His patience and persistence have paid off again.