Aims. We report the discovery of five new dwarf novae that were spectroscopically identified in the Hamburg Quasar Survey (HQS), and discuss the properties of the sample of new dwarf novae from the HQS.Methods. Follow-up time-resolved spectroscopy and photometry have been obtained to characterise the new systems.Results. The orbital periods determined from analyses of the radial velocity variations and/or orbital photometric variability are P-orb similar or equal to 105.1min or P-orb similar or equal to 109.9min for HS 0417+ 7445, P-orb = 114.3 +/- 2.7min for HS 1016 +/- 3412, Porb = 92.66 +/- 0.17 min for HS 1340+ 1524, P-orb = 272.317 similar or equal to 0.001 min for HS 1857+ 7127, and P-orb = 258.02 +/- 0.56 min for HS 2214+ 2845. HS 1857+ 7127 is found to be partially eclipsing. In HS 2214+ 2845 the secondary star of spectral type M3 +/- 1 is clearly detected, and we estimate the distance to the system to be d = 390 +/- 40 pc. We recorded one superoutburst of HS 0417+ 7445, identifying the system as a SU UMatype dwarf nova. HS 1016+ 3412 and HS 1340+ 1524 have rare outbursts, and their subtype is yet undetermined. HS 1857+ 7127 frequently varies in brightness and may be a ZCam-type dwarf nova. HS 2214+ 2845 is a UGem-type dwarf nova with a most likely cycle length of 71 d.Conclusions. To date, 14 new dwarf novae have been identified in the HQS. The ratio of short-period (< 3 h) to long-period (> 3 h) systems of this sample is 1.3, much smaller compared to the ratio of 2.7 found for all known dwarf novae. The HQS dwarf novae display typically infrequent or low-amplitude outburst activity, underlining the strength of spectroscopic selection in identifying new CVs independently of their variability. The spectroscopic properties of short-period CVs in the HQS, newly identified and previously known, suggest that most, or possibly all of them are still evolving towards the minimum period. Their total number agrees with the predictions of population models within an order of magnitude. However, the bulk of all CVs is predicted to have evolved past the minimum period, and those systems remain unidentified. This suggests that those post-bounce systems have markedly weaker H beta emission lines compared to the average known short-period CVs, and undergo no or extremely rare outbursts.

We report the discovery of one unique cataclysmic variable drawn from the Hamburg Quasar Survey, HS2331+3905. Follow-up observations obtained over three years unveiled a very unusual picture. The large amplitude 3.5 h radial velocity variations obtained from our optical spectroscopy is not the orbital period of the system, as one would normally expect. Instead, extensive CCD photometry strongly suggests that HS2331+3905 is a short orbital period cataclysmic variable with Porb = 81.09 min, containing a cold white dwarf which appears to exhibit ZZ Ceti pulsations.

HD 163621 is a double-lined spectroscopic binary in a circular orbit whose period is 3.3 days. Spectral classification of the components has proved difficult, but current results of K0 V and late K V are reasonably consistent with our best model of the system, which has spectral types of G8V and K7V. The object shows photometric variability and chromospheric activity and is therefore a member of the BY Draconis class of variables. The minimum masses are quite small, 0.10 and 0.07 M⊙ for the primary and secondary, respectively, suggesting an orbital inclination of about 30°. The system is synchronously rotating. Its distance is estimated to be 31 pc, which makes it an excellent candidate for a trigonometric parallax determination.

The paper presents photoelectric photometry of Lambda And never before published, obtained between February 1982 and December 1990 at 29 different observatories. Then it is combined with all other photometry available (previously published, contained in the I.A.U. Commission 27 Archives, and obtained with the Vanderbilt 16-inch automatic telescope but not yet published), to yield a 14.8-year data base. Analysis reveals a long-term cycle in mean brightness, with a full range of 0.15 m and a period of 11.4 +/- 0.4 years. Because most of the new photometry was concentrated in the 1983-1984 observing season, this one well-defined light curve is analyzed with a two-spot model. Spot A keeps a 0.04 m amplitude throughout four rotation cycles whereas the amplitude of spot B diminishes from 0.09 m down almost to 0.03 m. The spot rotation periods were 55.9 d +/- 0.6 d and 52.8 d +/- 1.0 d, respectively.

B andV photometry of DM UMa obtained between January, 1980 and June, 1984 is presented. Analysis yields a mean photometric period 7d.478±0d.010, compared to the known oribital period of 7d.492±0d.009. Light curves obtained during any two seasons do not agree in any of the following: shape, amplitude, phases of the light maxima and minima, mean light level, or brightness at the light maxima and minima. From the change inB-V over the photometric period, we concludethat the hemisphere visible during the light minimum is cooler than that seen during light maximum. The mean colorB-V=1m.065±0m.002 is consistent with K1 III or K2 IV. Phases of light minima lie on two well-separated groups with different slopes; the corresponding periods are 7d.471±0d.002 and 7d.481±0d.001, in dicating that both migrate linearly towards decreasing orbital phase. In terms of the starspot model this indicates that two respective centers of activity were situated at different longitudes and latitudes on a differentially rotating star. From circumstantial evidence we infer that the dark region seen from 1979 onwards disintegrated sometime between the 1982 and 1983 observing seasons, leaving behind an area of relatively high surface brightness. We can put a lower limit of about four years on the lifetime of a center of activity.

Photometrie dans la bande V de cette binaire de type RS CVn de longue periode, faites en 1981-82 et 1982-83 en plusieurs observatoires europeens et des Etats-Unis. Plusieurs cycles ont ete couverts

Five years of photoelectric photometry of this bright K1 III RS CVn binary has been obtained at thirteen different observatories. Except for one year, the light curve has shown two minima, separated by roughly a half cycle. At the epoch of discovery (1977.2) one minimum was shallower but as of 1980.2 the two became comparable in depth. During the 1979–80 season the light curve changed shape rapidly, the shallower minimum becoming as deep as the other within about 80 days or perhaps less. Times of both minima can be fit with a photometric period of 19 d .423, which is 0.9% shorter than the 19 d .603 orbital period. The overall brightness range during the five years has been 4 m .13<V<4 m .29.

Differential photometry of the KI IV-III RS CVn-type binary HR 7275 in 1978, 1979, and 1980 at nine different observatories shows it definitely to be variable, thus confirming the suspicion of Herbst. The photometric period determined two ways was 27 . d 91 or 27 . d 65, thus about 3% shorter than the spectroscopically determined orbital period of 28 . d 59. The total variation observed during the three years was 0 . m 22 in theV. The light curve was always asymmetrical, with a stillstand on the rising branch in 1978 but on the falling branch in 1980.