Abstract.A CCD photometric study of the dense galactic open cluster M 37 is presented and discussed. The majority of the analysed data are time-series measurements obtained through an RC filter. The observations were carried out on seven nights between December 1999 and February 2000, and have led to the discovery of 7 new variable stars in the field. Three of them have been unambiguously identified as W UMa-type eclipsing binaries, while two more are monoperiodic pulsating stars, most probably high-amplitude δ Scuti-type variables. The remaining two stars seem to be long-period eclipsing binaries without firm period determination. Johnson B and V frames have been used to construct a new colour-magnitude (CM) diagram of the cluster, and to find the locations of the new variable stars. The pulsating variables are most likely background objects. The CM diagram is fitted with recent isochrones yielding the main parameters of the cluster.

Abstract. We present low-and medium resolution spectra of the recurrent nova CI Aquilae taken at 14 epochs in May and June, 2000. The overall appearance is similar to other U Sco-type recurrent novae (U Sco, V394 CrA). Medium resolution (λ/∆λ ≈ 7000-10 000) hydrogen and iron profiles suggest an early expansion velocity of 2000-2500 km s −1 . The Hα evolution is followed from ∆t = −0.6 d to +53 d, starting from a nearly Gaussian shape to a double peaked profile through strong P-Cyg profiles. The interstellar component of the sodium D line and two diffuse interstellar bands put constraints on the interstellar reddening which is estimated to beThe available visual and CCD-V observations are used to determine t0, t2 and t3. The resulting parameters are: t0 = 2451669.5 ± 0.1, t2 = 30 ± 1 d, t3 = 36 ± 1 d. The recent lightcurve is found to be generally similar to that observed in 1917 with departures as large as 1-2 mag in certain phases. This behaviour is also typical for the U Sco subclass.

Aims. We define the relationship between the double-mode pulsation of Cepheids and metallicity in a more accurate way, determine the empirical metallicities of double-mode Cepheids from homogeneous, high-resolution spectroscopic data, and study of the periodratio -metallicity dependence. Methods. The high S /N echelle spectra obtained with the FEROS spectrograph were analyzed using a self-developed IRAF script, and the iron abundances were determined by comparing with synthetic spectra assuming LTE. Results. Accurate [Fe/H] values of 17 galactic beat Cepheids were determined. All these stars have solar or slightly subsolar metallicity. Their period ratio (P 1 /P 0 ) shows strong correlation with their derived [Fe/H] values. The corresponding period ratio -metallicity relation has been evaluated.