CBA Belgium Observatory
Detection of superhumps in DM Dra during its November 2001 outburst


DM Dra outburst. 2001, November 14
O.35-m f/6.3 telescope - unfiltered SBIG ST-7 CCD
Composite of 5 exposures of 40 sec each.

On 2001, November 14.176 UT, Timo Kinnunen (Finland) reported a rare outburst of the large-amplitude dwarf nova DM Dra on VSNET. The previous outburst of DM Dra was spotted in October 2000 by Patrick Schmeer (vsnet-alert 5338). 

DM Dra was originally discovered by Stepanyan, as SVS 2426, and  spectroscopic observations revealed an O-B star, which is consistent
with the dwarf nova classification. In quiescence, the object is around mag 20. CCD photometry in quiescence by Howell et al. (PASP 102, 758)
showed the object at V=20.8, and suggested a possible periodicity of 125
min. Howell also reported a temporary fading of 0.4 mag in 5 min, which might have been due to an eclipse.

I started a CCD photometry session on DM Dra on 2001, November 14/15, using the 0.35-m f/6.3 telescope at CBA Belgium Observatory. FITS images were acquired with an ST-7 CCD camera without filters, under perfect skies.

I accumulated 4.1 hours of observations (269 datapoints), resulting in the light curve at right. The observations clearly revealed the presence of genuine, single-peaked superhumps with an amplitude of 0.36 mag, and a period of 0.0734 +/- 0.0030 d (PDM technique). This value substantially differs from the one obtained by Howell et al. during quiescence (see above). The above observations firmly establish DM Dra as a new SU UMa type dwarf nova.  

Period diagram of DM Dra (Nov 14/15, 2001),
 showing superhump period at 0.0734 d.

Phase diagram of DM Dra (Nov 14/15, 2001)
Single-peaked superhump

I'm grateful to Timo Kinnunen for promptly notifying this outburst.

  (c) Copyright Tonny Vanmunster, 2001