[vsnet-alert 7444] V2540 Oph - detection of period/s

[Alon Retter <retter@Physics.usyd.edu.au>]

Dear southern observers,
 
Continuous CCD photometry carried out by Marc Bos (Mt Molehill 
Observatory, New Zealand) during 4 nights (22 hours) and Tom Richards
(Woodridge Observatory, Australia) during 1 night (6 h) in July on V2540
Oph (Nova Oph 2002) with no filter shows a periodic modulation with a full 
amplitude of ~0.02 mag. The corresponding frequency is ~10.1 c/d (~2.4 h)
or the 1-d alias at ~9.1 c/d (~2.6 h). There are probably more periods.
There is a peak at ~4 c/d - 6 h, but it is questionable as it is about the
length of the individual runs. Other possible periods - ~14, 18, 20, 28,
35 ... c/d.

The ~2.5-h period could be the binary orbital period. It would be then in
the period gap of cataclysmic variables. If other periods are confirmed
the nova would be an intermediate polar supporting the possible connection
between the transition phase in novae and intermediate polars. As
observations of 3 recent novae (V1494 Aql 1999/2, V382 Vel 1999, V1039 Cen
2001) are consistent with this prediction, V2540 Oph will be the 4th
case, so the proposed connection becomes highly significant.

The detection of periods at this early stage of the nova (~2 mags below
the observed maximum) probably means that the real maximum must have been
missed. This explains the appearance of the oscillations in the transition 
phase soon after discovery.

More observations are strongly encouraged to confirm the presence of the 
candidate periodicities. The nova is still very bright (V~11.2) and an
ideal object for a small telescope equipped with a CCD. Cor (2000):   
17:37:34.5  -16:23:22.  

Regards,
Alon
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   Dr. Alon Retter          Tel. (work)     +61-2-9351-4058
   School of Physics        Fax  (work)     +61-2-9351-7726
   University of Sydney     -------------------------------------------
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