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Astron. Astrophys. 348, 917-923 (1999)

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On the origin of X-ray dips in Her X-1

N.I. Shakura 1, M.E. Prokhorov 1, K.A. Postnov 2 and N.A.Ketsaris 1

1 Sternberg Astronomical Institute, Moscow University, 119899 Moscow, Russia
2 Faculty of Physics, Moscow State University, 119899 Moscow, Russia

Received 10 December 1998 / Accepted 25 June 1999


A strong X-ray illumination of the optical star atmosphere in Her X-1, asymmetric because of a partial shadowing by the tilted twisted accretion disk around central neutron star, leads to the formation of matter flows coming out of the orbital plane and crossing the line of sight before entering the disk. We suggest that the absorption of X-ray emission by this flow leads to the formation of pre-eclipse and anomalous dips of type I. These dips are observed during several orbits after turn-on both in the main-on and short-on state. Almost coherent action of tidal torques and matter streams enhances the disk wobbling which causes the disk edge to shield the X-ray source after the turn-on. Anomalous dips of type II and post-eclipse recovery appear due to this process only on the first orbit after turn-on.

Key words: stars: neutron – stars: individual: Her X-1

Send offprint requests to: N.I. Shakura (shakura@sai.msu.su)

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© European Southern Observatory (ESO) 1999

Online publication: August 13, 199