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Optical flickering and shot noise in AM Her systems

Published online by Cambridge University Press:  12 April 2016

S. Larsson
Affiliation:
Stockholm Observatory, S-13336 Saltsjöbaden, Sweden
B. Larsson
Affiliation:
Stockholm Observatory, S-13336 Saltsjöbaden, Sweden

Extract

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The emission from AM Her systems show a variety of time-variable phenomena, including flickering with a typical power spectrum slope of −1 to −2. The optical flickering is usually modeled as, or assumed to be, a shot noise process with many overlapping simultaneous shots. Panek (1980) found that, for AM Her, a consistent model could be constructed with randomly occurring 70… 90 s rectangular shots. The power spectrum had a v−2 shape above 0.02 Hz as expected, although it is not clear whether a break in the slope of the power spectrum was actually seen around 0.01 Hz. There are many additional reports in the literature of ‘characteristic time-scales’ on the order of tens of seconds. However we are not aware of any case where the reported time-scale has been supported by e.g. a break in the power density spectrum. It is easy to show that the usual method of estimating a ‘characteristic time-scale’ from the auto correlation function of de-trended data will suggest such a characteristic time-scale even if none is present in the original time series. The evidence for shot noise in AM Her light curves therefore needs a re-examination. In this paper we give a short summary of our analysis of optical flickering in V834 Cen, based on high speed photometry obtained at ESO in 1987. Details will be reported elsewhere.

Type
Polar Systems
Copyright
Copyright © Kluwer 1996

References

Panek, R., 1980, Ap. J., 241, 1077 Google Scholar