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ATEL # 3032; A.A.Nucita (Unisalento), B.M.T. Maiolo (Unisalento), E. Kuulkers (Esac)
on 15 Nov 2010; 15:31 UT
Password Certification: Achille Nucita (firstname.lastname@example.org)
Subjects: X-ray, Cataclysmic Variables
Analysis of archival XMM-Newton data (OBSID 0205770101) of the cataclysmic variable Z Cha in quiescence in 2003 confirms the existence of X-ray eclipses consistent with occultation of the white dwarf, as seen previous with the ROSAT/HRI (van Teeseling et al., 1996, A&A, 315, 467). The high quality XMM-Newton data show also drops in the light curve, i.e., dips in the orbital phase range 0.6-0.9 which are due to absorption of the X-ray photons by intervening matter along the line of sight. Such dips were present in the ROSAT/HRI too, albeit at a very low confidence level due to the poor photon statistics. The XMM-Newton data furthermore show the existence of a secondary dip around the phase 0.3, not reported before. The observed dips, and their location, are consistent within the model proposed by Frank, King & Lasota (1987, ApJ 178, 137). According to this model, the mass transfer stream hits the edge of the accretion disk and the material settles into an inner ring whose radius depends on the orbital period and the accretor mass. A two phase medium of cold clouds and hot intercloud gas forms (after ionization instabilities) off the disk plane after the mass impacts on the inner ring. We encourage further X-ray observations of this system, as well as observations of other similar high-inclination cataclysmic variables to confirm the dip phenomena near phase 0.3.