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Session 12 - Degenerate Stars & Supernovae.
Oral session, Monday, June 09
North Main Hall C/D,
Both the 1.24 sec pulsational period and the 35 day turn-on period of Her X-1 show long-term variability. It is shown that both periods vary in a highly correlated way: when the spin-up rate drops the 35 day precessional period gets shorter. This correlation is most evident on long time scales ( 2000 days), e.g. during two extended spin-down episodes, but also on shorter time scales (a few hundred days) on which quasi-periodic variations are apparent. The likely common cause are variations of the rate of mass accretion onto the neutron star. A physical explanation within the framework of the coronal wind model is proposed. Further details on the jitter of the 35 day clock will be discussed.
