Special Notice #43: Possible Super Outburst of BZ UMa

April 14, 2007

The cataclysmic variable star BZ UMa is currently experiencing an outburst which is peculiar for that star. Historically, BZ UMa has outbursts every 312 +/-114 days (although it has been much more regular in the past decade). These outbursts are similar to regular UGSU outbursts with a fast rise and a short decay over four days and are absent of any superhumps or other periodicity. However, no superoutbursts of the type also associated with UGSU stars have been detected in BZ UMa despite good observational coverage since 1972.

The current outburst began on April 10, 2007, which is about the expected time for its next outburst. However, instead of a fast rise typical for BZ UMa, it has continued to slowly rise after four days and has already reached magnitudes brighter than normal for its other outbursts. Also, preliminary data analysis by M. Koppelman shows the possibility of superhumps emerging. It is seeming more and more likely that this is the long awaited first detected superoutburst of BZ UMa!

CCD observations *for as long as possible* are requested. A V filter is preferred but unfiltered is acceptable if your system is not setup with a V filter. Set your exposure time for as short as possible to gain an SNR>=100. AAVSO charts are here:

obsolete link: [http://www.aavso.org/cgi-bin/searchcharts3.pl?name=0846%2B58]

2016 link: https://www.aavso.org/vsp

There has been much debate over the nature of BZ UMa over the years. It has been alternately classified as a UGSU, an intermediate polar and various combinations thereof. It has also been heavily observed at multiwavelength bands, yet all they have been able to detect are abnormal spectral signatures which have yet to be explained.

In the past, quasiperiodic oscillations have been detected in BZ UMa's outbursts, separated by periods of inactivity during the decline. The QPO activity characteristics changes outburst to outburst. In addition, it displays intensive flickering which doesn't change much during the outburst, again peculiar for a UGSU CV.

A summary of recent AAVSO campaigns on this star, analysis of the data and published literature was presented in a poster at the May, 2005 AAS meeting by A. Price and S. Howell. The poster is online at this URL:

obsolete link: http://www.aavso.org/news/price-aas.pdf

Clear skies!
Aaron Price


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