BELGIAN ASTRONOMICAL SOCIETY V.V.S. - Working Group Variable Stars Cataclysmic Variables Circular No.166 1998, April 06 Ed.: T. Vanmunster, Walhostraat 1A, 3401 Landen, BELGIUM Internet: tvanmuns@innet.be TEL. 32-11-831504 CVC Web Page : http://www.cba.phys.columbia.edu/cvc =================================================================== BZ UMa [UGSU:, 10.5v - 17.8v] ============================= Eric Broens, Mol, Belgium reports the detection by Eddy Muyllaert, Belgium of an outburst of BZ UMa. This interesting dwarf nova is a possible SU UMa-type cataclysmic variable. Eric Broens has been able to confirm the outburst through clouds. Available observations : 1998 Apr 05.476 UT, [15.7 (G. Hanson, 0.46-m refl.); Apr 06.854 UT, 12.2 (E. Muyllaert, C-11 telescope, AAVSO seq); Apr 06.869 UT, 12.1: (E. Broens, 0.35-m reflector, AAVSO seq); According to our records, the previous outburst of BZ UMa was observed by G. Hanson, USA on January 9, 1997 [CVC 122] at mag 14.4 (brightening to mag. 11.6 shortly afterwards). Unfiltered time-series CCD photometry at the CBA Belgium Observatory during that outburst did not reveal any superhumps [CVC 127]. Ringwald et al. [1] point out that BZ UMa has very infrequent outbursts, lasting 10-20 days, with large amplitudes (delta V approx. 6 mag.). He further notes that superhumps have eluded detection in BZ UMa, but may well exist. He finds an orbital period of 0.0679 days. BZ UMa does have normal outbursts as well as superoutbursts, as can be derived from the long-term lightcurve of BZ UMa, published in [2]. Given the fact that the SU UMa-type nature of BZ UMa is still unclear, and that no superhumps have been detected so far in this system, it is evident that close photometric monitoring by CCD is of utmost importance ! References ---------- [1] Ringwald, F.A., et al., 1994, MNRAS, 271, 323-342 [2] Jurcevic et al., 1994, PASP, 106, 481. Editorial absence +++++++++++++++++ Please note that the Editor will be absent from April 14 till April 18. Tonny Vanmunster