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Context. We investigate the distribution of blue straggler stars in the field of three open star clusters.

Aims.We analyse the point-symmetric planetary nebula NGC 6309in terms of its three-dimensional structure and of internal variations of the physical conditions to deduce the physical processes involved in its formation.

Aims.Identification of the structural components and analysis of the internal kinematics in the planetary nebula IC 5217.

We analyse CCD broad band ($U\!BV(RI)_{\rm C}$) photometric data obtained in the fields of the poorly studied open clusters NGC 2425and NGC 2635. Both clusters are found to be of intermediate age thus increasing the population of open clusters known to be of the age of, or older than, the Hyades. More explicitly, we find that NGC 2425is a 2.2 Gyr old cluster, probably of solar metallicity, located at 3.5 kpc from the Sun. NGC 2635is a Hyades age (600 Myr) cluster located at a distance of 4.0 kpc from the Sun. Its Colour Magnitude Diagram reveals that it is extremely metal poor for its age and position, thus making it a very interesting object in the context of Galactic Disk chemical evolution models.

CCD BVIphotometry of the faint open clusters Berkeley 73, Berkeley 75 and Berkeley 25 are presented. The two latter are previously unstudied clusters to our knowledge. While Berkeley 73 is found to be of intermediate-age (about 1.5 Gyr old), Berkeley 75 and Berkeley 25 are old clusters, with ages greater than 3.0 Gyr. We provide also estimates of the clusters size. All these clusters lie far away from the Galactic Center, at $R_{\rm GC} \geq 16$kpc, and quite high on the Galactic plane, at $|Z_{\odot}| \geq 1.5$kpc. They are therefore important targets to probe the properties of the structure of the Galaxy in this direction, where the Canis Major over-density has been discovered to be located.

CCD UBVIimaging photometry was carried out in the fields of the open clusters Pismis 8 and Pismis 13, located in the Vela-Puppis region in our Galaxy. MKspectral types have also been determined for a number of stars located in the fields of these two clusters which were used to secure membership among the brightest stars. Since our photometry goes to a fainter limit than previous studies we could provide better reddening, distance and age determinations. Both clusters are located close to the edge of the local arm in the third quadrant. Pismis 8 is a cluster about 5–7 My old located at 2000 pc from the Sun, while Pismis 13 was found at 2750 pc with a probable age of about 100 My. The estimate of the slopes of the mass functions in both cases yielded $x\approx 1.7$and $x\approx 2.1$for Pismis 8 and 13 respectively.

Deep CCD $\it UBV(RI)_{\rm C}$photometry has been carried out in the area of the open cluster Stock 16. The different photometric diagrams indicate the presence of three superimposed stellar groups, all composed of early type stars. The first of them, the cluster Stock 16, suffers from slightly variable reddening with a mean color excess $ \langle E_{B-V}\rangle = 0.51~$. The second group, reddened by $ \langle E_{B-V}\rangle = 0.84~$, includes the Wolf-Rayet star WR 50 (a WC7+OB), and the third one, with a mean $ \langle E_{B-V}\rangle = 1.18~$, also includes another Wolf-Rayet star, WR 51 (a WN4+OB?). Our results confirm the distance and reddening already stated for Stock 16 but include new members. Concerning the other two highly reddened groups, we show that the first one – located at a distance of 3600 pc – is probably related to an anonymous OB association behind Cen OB1 also at 3600 pc already mentioned in the literature; the other seems to be a distant OB association – at more than 9000 pc – which may belong to the Scutum-Crux spiral arm. In these two groups we find evidence that the absorption law, $A_V/E_{B-V} = R$amounts to 4.0 approximately. The ages of the different star populations in the zone range from $5 \times 10^6$yr to $6.4 \times 10^6$yr for Stock 16, $8 \times 10^6$for the second most reddened group and $5 \times 10^6$for the probable association in Scutum-Crux. A determination of the IMF slope of Stock 16 was also carried out for stars in the mass range $ 1.8 < M < 14~$$M_{\odot}$, giving a normal value $x = 1.3$.

We present CCD broad band photometric observations in the fields of the Third Galactic Quadrant open clusters NGC 2580 and NGC 2588 (V(I)Cand UBV(RI)Crespectively). From the analysis of our data we found that NGC 2580 is located at a distance of about 4 kpc and its age is close to 160 Myr. As for NGC 2588, it is placed at about 5 kpc from the Sun and is 450 Myr old. This means that NGC 2588 belongs to the extension of the Perseus arm, whereas NGC 2580 is closer to the local arm structure. The luminosity functions (LFs) have been constructed for both clusters down to $V \sim 20$together with their initial mass functions (IMFs) for stars with masses above $M \sim 1$–1.5 $M_{\odot}$. The IMF slopes for the most massive bins yielded values of $x \approx 1.3$for NGC 2580 and $x \approx 2$for NGC 2588. In the case of this latter cluster we found evidence of a core-corona structure produced probably by dynamical effect. In the main sequences of both clusters we detected gaps, which we suggest could be real features.

We present (UBVRI) multicolor linear polarimetric data for 26 of the brightest stars in the area of the open cluster Stock 16 that were considered to study the properties of the ISM (interstellar medium) towards the cluster. Our data yield a mean polarization percentage of $P\sim2.5\%$, close to the polarization value produced by the ISM with normal efficiency ($P_{\lambda_{\rm max}} \sim 5 E_{B-V}$) undergoing a color excess of $E_{B-V} =0.51$. The mean angle of the polarization vectors, $\theta= 74\fdg9$, agrees quite well with the expected angle produced by dust particles aligned in the direction of the galactic disk (and the magnetic field) in the region. A study of the extinction suffered by the stars in the zone was also performed combining our new data with previous photometric data. In this sense, our analysis indicates that the visual absorption affecting Stock 16 stars is mainly produced in front of the cluster by a dust cloud at approximately 500 pc from the sun. The large polarization value of the nonmember star, WR 51, confirms its background star nature.

Deep and extensive CCD photometric observations at $UBV(RI)_{\rm C}{\rm H}_{\alpha}$were carried out in the area of the open cluster NGC 3293. The new data set allows to see the entire cluster sequence down to $M_{V} \approx +4.5$, revealing that stars with $M_{V} < -2$are evolving off the main sequence; stars with $-2 < M_{V} < +2$are located on the main sequence and stars with $M_{V} > +2$are placed above it. According to our analysis, the cluster distance is $d = 2750$±$250~{\rm pc}$($V_{0}-M_{V} = 12.2$±0.2) and its nuclear age is 8 ±1 Myr. NGC 3293 contains an important fraction of pre–main sequence (PMS) stars distributed along a parallel band to the ZAMS with masses from 1 to $2.5~\cal M_{\odot}$and a mean contraction age of 10 Myr. This last value does not differ too much from the nuclear age estimate. If we take into account the many factors that may affect the PMS star positions on the colour–magnitude diagram, both ages can be perfectly reconciled. The star formation rate, on the other hand, suggests that NGC 3293 stars formed surely in one single event, therefore favouring a coeval process of star formation. Using the ${\rm H}_{\alpha}$data, we detected nineteen stars with signs of ${\rm H}_{\alpha}$emission in the region of NGC 3293, another indication that the star formation process is still active in the region. The computed initial mass function for the cluster has a slope of $x = 1.2 \pm 0.2$, a bit flatter than the typical slope for field stars and similar to the values found for other young open clusters.

The kinematics and physical conditions of the bipolar planetary nebula M 2-48 are analysed from high and low dispersion long-slit spectra. Previous CCD narrow-band optical observations have suggested that this nebula is mainly formed by a pair of symmetric bow-shocks, an off-center semi-circular shell, and an internal bipolar structure. The bipolar outflow has a complex structure, characterised by a series of shocked regions located between the bright core and the polar tips. There is an apparent kinematic discontinuity between the bright bipolar core and the outer regions. The fragmented ring around the bright bipolar region presents a low expansion velocity and could be associated with ejection in the AGB-PN transition phase, although its nature remains unclear. The chemical abundances of the central region are derived, showing that M 2-48 is a type I planetary nebula (PN).

A deep CCD UBVRIphotometric survey combined with UBVRIpolarimetric observations of 21 bright stars was carried out in the region of the open cluster Havlen-Moffat No. 1. Our data reveal that the extinction law in this cluster is variable and that six cluster stars show very high polarisation values (>4% ), probably because of the presence of a nearby small dust cloud. The cluster is at a distance of $d = 3300$pc, it is 2-4 Myr old and the initial mass function of its most massive stars (${\cal M} > 3 {\cal M_{\sun}}$) has a flat slope of $x\approx 0.7$. As an additional result, it was possible to reconcile the absolute magnitudes of the two WN7-type members using the $R-$values valid in the regions where they are located.