The June 2001 outburst of V478 Her : likely detection of superhumps
|On 2001, June 4.9599 UT, R. Diethelm
(Switzerland) reported a brightening of the cataclysmic variable V478 Her
(AAVSO News Flash No. 793). He found the object at mag 15.70 on his CCD
images, compared to mag 17.6: on a May 19th CCD image.
V478 Her previously was classified as an irregular variable (IS:), with a variability range of mag 15.5 - 17.1p.
On June 6.976 UT, we were able to confirm the outburst of V478 Her, using the 0.35-m f/6.3 SCT and unfiltered ST-7 CCD of CBA Belgium Observatory. The image at left is a composition of 5 exposures of 90 seconds each, and has North up. The location of the variable is indicated. The variable was estimated to be mag 15.85 (unfiltered).
Due to the unfavourable weather conditions, we could not undertake a more extensive photometry session.
|On June 8th, 2001, the night was very clear over CBA Belgium
Observatory, so we decided to start an all-night long photometry
session on V478 Her, to study the outburst characteristics of V478 Her. We
knew that virtually nothing was known about this variable.
The resulting light curve (see diagram at right) covers 3.7 hours and clearly shows a 0.33-mag modulation, that very likely is to be attributed to superhumps, thus classifying V478 Her as a new member of the UGSU-type dwarf novae. Due to the short nights in Belgium, during this period of the year, we could not follow the variable for a longer duration, but we hope that contributions from other observatories will help in securing the classification of the variable.
Using Stellingwerf's PDM algorithm, we derived a preliminary superhump period value of 0.129 +/- 0.005 d or about 3.1 hours. This puts V478 Her near the upper limit of the so called 'period gap'.
Needless to say that this variable deserves much more
attention and that we strongly recommend to monitor it in detail during the next
(c) Copyright Tonny Vanmunster, 2001