[Aavso-photometry] CBA campaign on LL And - new observations. Superhump period and fractional superhump excess update

[Tonny Vanmunster]

Dear colleagues,

The CBA campaign on LL And continues to generate new observations, despite
the unfavourable location of the target. New data sets have been supplied by
Jonathan Kemp / Sarah Tuttle (MDM Observatory, 1.3-m telescope) and Tonny
Vanmunster (CBA Belgium Observatory, 0.35-m telescope), bringing the total
amount of CCD observations to 2800.

The new observations show full-developed superhumps, with a mean amplitude
of 0.26 mag. Using Peranso's ANOVA method, we derive a superhump period
value of 0.05654 +/- 0.00012 d. The corresponding period- and phase diagrams
are shown at www.cbabelgium.com.

Our superhump period value is shorter than the value of 0.05697 d derived at
Kyoto University on the basis of CCD observations from 1993, and is likely
more accurate (we use 7x more observations, covering a longer time span
too). Assuming an orbital period of 0.055053 d, the Kyoto Univ fractional
superhump excess value was 3.5%, which is unusually large for a short-period
system. It triggered a discussion on the location of LL And on the
evolutionary track of binary systems (see
http://arxiv.org/abs/astro-ph/0310626). However, our superhump period value
now yields a fractional superhump excess value of 2.7%, which is quite
common for an UGSU-type dwarf nova.

Further time-series CCD observations of LL And are strongly encouraged. If
the present superoutburst turns out to last for another week or so, the
object might even classify as a possible UGWZ-type dwarf nova. Time will
tell.

Best regards,
Tonny Vanmunster
(on behalf of the CBA)


Tonny Vanmunster
CBA Belgium Observatory
http://www.cbabelgium.com
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PERANSO : The Final Frontier of Period Analysis Software
http://www.peranso.com
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