Outburst of BZ UMa (1997 Jan.)

The suspected SU UMa-type dwarf nova BZ UMa is undergoing a rare outburst as reported by G. Hanson ( vsnet-obs 4781).

from CVC 122 (VVS Belgium)

(also vsnet-alert 671)

BZ UMa [UGSU:, 10.5v - 17.8v]

Gene Hanson, Arizona, USA reports his detection of an outburst of this interesting dwarf nova (possible SU UMa type). Tonny Vanmunster, CBA Belgium has confirmed the outburst, using a 25-cm f/6.3 telescope and ST-7 (unfiltered) CCD. Available observations :

1997 Jan 08.213 UT, [14.1  (G. Hanson, seq: AAVSO);
     Jan 09.194 UT,  14.4: (G. Hanson);
     Jan 09.202 UT,  14.2  (G. Hanson);
     Jan 09.560 UT,  11.6  (G. Hanson);
     Jan 09.791 UT,  11.9  (T. Vanmunster, unfiltered CCD image);

The previous outburst of BZ UMa was observed by T. Burrows, USA on May 14, 1996 [CVC 94] at mag. 13.7 (brightening to mag. 11.9 in 2.7 hours). It was a normal outburst, that lasted for 4 days only [CVC 96], reaching a maximum magnitude of 10.6.

In a recent publication, 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 if the present outburst is a superoutburst, it should be searched for superhumps. Close photometric monitoring is of utmost importance !

[1] Ringwald, F.A., et al., 1994, MNRAS, 271, 323-342
[2] Jurcevic et al., 1994, PASP, 106, 481.

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