... variables

Partly based on observations at ESO telescopes.

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...

Figures A.1, A.2, and A.7 to A.21 are only available in electronic form at http://www.edpsciences.org

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...2,

Present address: Astronomical Institute, Osaka Kyoiku University, Asahigaoka 4-698-1, Kashiwara, Osaka 582-8582, Japan.

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... centre

The high velocity wings in SW Sex systems are an important exception (e.g. Hoard et al. 2000, and references therein).

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...)

The uncertainties in the determination of the continuum (which was measured with a graphics cursor) are hard to quantify, but the fact that all three data sets show the same basic features at identical phases proves the reality of this variation.

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... 0.3-0.7)

An extension of the Doppler tomography method to account for emission components with variable strength has been very recently proposed by Steeghs (2003).

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... suspected

Doppler tomography has been published for none of these systems, so that the evidence on their emission distribution is only secondary. This emphasizes the need for more detailed line-profile studies for short period CVs.

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... quiescence

Emission from the secondary star has possibly also been detected in the SU UMa dwarf nova OU Vir ( $P_{\rm orb}$ = 1.75 h) by Mason et al. (2002). However, the authors are very cautious with their interpretation due to the problematic definition of the fiducial phase in this system.

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