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Paper: Detection of spiral structure in the quiescent accretion disk of IP Pegasi
Volume: 261, The Physics of Cataclysmic Variables and Related Objects
Page: 513
Authors: Neustroev, V. V.; Borisov, N. V.; Barwig, H.; Bobinger, A.; Mantel, K. H.; šimíc, D.; Wolf, S.
Abstract: We present the results of the spectral investigations of the cataclysmic variable IP Pegasi in quiescence. Optical spectra obtained on the 6-m telescope at the Special Astrophysical Observatory (Russia), and on the 3.5-m telescope at the German-Spanish Astronomical Center (Calar Alto, Spain), have been analysed by means of Doppler tomography and phase modeling technique. The Balmer Doppler maps show the two bright emitting regions superposed to the typical ring-shaped emission of the accretion disk (Fig. 1). The Brighter of them can be unequivocally contributed to emission from the bright spot on the outer edge of the accretion disk. The second spot is located far from the region of interaction between the stream and the disk particles. This feature was interpreted by Wolf et al. (1998) as beginning of the formation of spiral arm in the outer disk. However the second spiral arm detected by Steeghs, Harlaftis, & Horne (1997) during outburst, is not visible on our tomograms. Probably it is hidden in the intensive emission of the bright spot. We have modeled emission line profiles and have found a dependence of brightness of the spot from the orbital phase (Fig. 2). We have detected, that while the spot is on the distant half of the accretion disk, it is almost not visible. Apparently, it is connected to an eclipse of the bright spot by an outer edge of the accretion disk. Further we have constructed new Doppler maps, using only spectra obtained during phases of minimum brightness of the spot. Although the used spectra practically do not contain an information about the bright spot, in the left side of tomograms can be seen the area of the increased luminosity (Fig. 1). However its location has varied. It was displaced downwards and has taken practically a symmetrical position concerning the second region of the increased luminosity. We think that we managed to obtain an image of the second spiral arm. Thus, our observations confirm the spiral structure of the quiescent accretion disk of IP Peg.
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