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Astron. Astrophys. 356, L33-L36 (2000)

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Letter to the Editor

Spirals and the size of the disk in EX Dra

V. Joergens 1,2, H.C. Spruit 1 and R.G.M. Rutten 3,4

1 Max-Planck-Institut für Astrophysik, Postfach 1523, 85740 Garching bei München, Germany
2 Max-Planck-Institut für Extraterrestrische Physik, Postfach 1603, 85740 Garching bei München, Germany
3 Netherlands Foundation for Research in Astronomy
4 Royal Greenwich Observatory, Apartado de Correos 321, 38780 Santa Cruz de La Palma, Canary Islands, Spain

Received 3 August 1999 / Accepted 10 March 2000

Abstract

Observations at high spectral and temporal resolution are presented of the dwarf nova EX Dra in outburst. The disk seen in the HeI line reconstructed by Doppler tomography shows a clear two-armed spiral pattern pointing to spiral shocks in the disk. The Balmer and HeII maps also give evidence for the presence of spirals. The eclipse as seen in the red continuum indicates a disk radius of 0.31 times the orbital separation, which might be large enough to explain the observed spiral shocks through excitation by the tidal field of the secondary. The eclipse in the Balmer line profiles, well resolved in our observations, indicates a somewhat smaller disk size (0.25). We discuss the possibility that this is related to an optical depth effect in the lines.

Key words: accretion, accretion disks – hydrodynamics – stars: binaries: eclipsing – stars: individual: EX Dra

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© European Southern Observatory (ESO) 2000

Online publication: April 10, 2000
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