Other
Scientific paper
Oct 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994pasp..106.1075r&link_type=abstract
Astronomical Society of the Pacific, Publications (ISSN 0004-6280), vol. 106, no. 704, p. 1075-1084
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48
Cataclysmic Variables, Long Term Effects, Periodic Variations, Stellar Activity, Stellar Luminosity, Stellar Magnitude, Stellar Mass Ejection, Stellar Oscillations, Eclipsing Binary Stars, Light Curve, Magnetic Effects, Solar Cycles, Stellar Mass Accretion
Scientific paper
Recent interest in long periods which may be present in cataclysmic variables has been motivated principally by the idea that solar-like magnetic cycles might be important. For the brighter members of the class, light curves compiled from amateur visual observations are an ideal resource for testing the presence of such periods. Because of the sheer immensity of the data, and the relative constancy of the average human eye over decades, the detection limits are more sensitive than could be achieved by any feasible photographic or photoelectric means. Here we present results for four well-studied stars, and evaluate the case for periods in other CVs. The conclusion from all of this is that none of the stars studied to date exhibits a good case for strictly periodic variability, and it is not even clear whether there is a preferred time scale. Nevertheless, the observed amplitudes (0.2 mag) and apparent time scales (5-40 yr) of variability are plausible consequences from solar-like magnetic cycles. We propose that the observed light variations on decade time scales are produced by the same mechanism which underlies the decade-time-scale orbital period changes seen in eclipsing binaries. In particular, we extend a theory of Porb changes to the case of accretion-powered binaries, and show that it predicts accretion-rate variations of amplitude Delta M-dot/M-dot approximately equal to 0.1, consistent with observation. The proximate cause of the Porb and M-dot variations is the cyclic transfer of angular momentum to and from the outer layers of the contact star. The underlying cause of these phenomena is solar-type cycles of the contact star.
Applegate James H.
Patterson Joseph
Richman Hayley R.
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