Superhumps in VY Aquarii

Citations Over TimeTop 25% of 1993 papers

Abstract

For many years VY Aquarii has been regarded as a charter member of the class fo recurrent novae, because it erupted several times, with outburst amplitudes of ~8 mag, exceeding those normally attributed to dwarf novae. We present observations obtained both in quiescence and eruption that emphasize the great similarity of the star to well-credentialed dwarf novae like WZ Sagittae. Long-term visual and photographic coverage shows two types of eruptions, differing in brightness and timescale by a factor of ~5. A transient wave in the quiescent light curve suggests a period in the range 80-120 minutes, which could be the orbital period of the underlying binary. Photometry during a long eruption in 1986 showed a large-amplitude modulation ("superhump") with a period of 92.7 (or possibly 99.1) minutes, which slowly decreased during the eruption. These are normal signatures of SU Ursae Majoris stars, a subclass of dwarf novae. The superhumps observed in SU UMa stars appear to show a similar degree of period instability, such that P ~ -(3-10)X10-5. Perhaps a more physically significant expression of this is a period-magnitude law: the periods decrease by 0.64±0.10% per magnitude of decline,_ at least during the early decline. This is a plausible decrease to expect from the precessing-disk model for the origin of superhumps, assuming the disk to be largest near maximum light.

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