During the last years and decades several individual studies and large-scale spectroscopic surveys significantly improved our knowledge of the Galactic metallicity distribution based on open clusters. The availability of Gaia data provided a further step forward in our knowledge. However, still some open issues remain, for example the influence of radial migration on the interpretation of the observed gradients. We used spectroscopic metallicities from individual studies and from the APOGEE survey to compile a sample of 136 open clusters, with a membership verification based on Gaia DR2. Additionally, we present photometric metallicity estimates of 14 open clusters in a somewhat outer Galactic region. Eight age groups allow us to study the evolution of the metallicity gradient in detail, showing within the errors an almost constant gradient of about −0.06 dex/kpc. Furthermore, using the derived gradients and an analysis of the individual objects, we estimate a mean migration rate of 1 kpc/Gyr for objects up to about 2 Gyr. Here, the change of the guiding radius is clearly the main contributor. For older and dynamically hotter objects up to 6 Gyr we infer a lower migration rate of up to 0.5 kpc/Gyr. The influence of epicyclic excursions increases with age and contributes already about 1 kpc to the total migration distance after 6 Gyr. A comparison of our results with available models shows good agreement. However, there is still a lack of a suitable coverage of older objects, future studies are still needed to provide a better sampling in this respect.

Fundamental astrophysical parameters have been derived for 20 open clusters (OCs) using CCD UBV(RI) C photometric data observed with the 84 cm telescope at the San Pedro Mártir National Astronomical Observatory, México.The interstellar reddenings, metallicities, distances, and ages have been compared to the literature values. Significant differences are usually due to the usage of diverse empirical calibrations and differing assumptions, such as concerning cluster metallicity, as well as distinct isochrones which correspond to differing element-abundance ratios, internal stellar physics, and photometric systems. Different interstellar reddenings, as well as varying reduction and cluster-membership techniques, are also responsible for these kinds of systematic differences and errors.The morphological ages, which are derived from the morphological indices (δV and δ1) in the CM diagrams, are in good agreement with the isochrone ages of 12 OCs, those with good red clump (RC) and red giant (RG) star candidates. No metal abundance gradient is detected for the range 6.82 ≤ R GC ≤ 15.37 kpc, nor any correlation between the cluster ages and metal abundances for these 20 OCs.Young, metal-poor OCs, observed here in the third Galactic quadrant, may be associated with stellar over-densities, such as that in Canis Major (Martin et al.) and the Monoceros Ring (Newberg et al.), or signatures of past accretion events, as discussed by Yong et al. and Carraro et al.

We present the results of a temporal and spectral analysis of the transient source ULX-4 in the galaxy M51. The data used were drawn from Chandra, XMM-Newton and Swift-XRT archives, spanning the years 2000-2019. The X-ray flux of the source is seen to vary by two orders of magnitudes within a month but a short-term variability was not observed over the time intervals of 100-2000 second in the 0.3−10 keV energy band. We find some evidence for the existence of bi-modality feature in the flux distribution of ULX-4. We identified two optical sources as possible counterparts within an error radius of 0.″18 at 95${{\ \rm per\ cent}}$ confidence level for ULX-4 based on the archival HST/ACS and HST/WFC3 data. Blackbody fits of the spectral energy distributions (SEDs) indicate the spectral type to be B-type stars. One of these counterparts exhibits a low-amplitude optical periodicity of 264 ± 37 days in the F606W filter; if we assume this apparent periodicity is associated with the orbital motion of the donor, then it is more likely that the donor is a red supergiant satisfying the long periodicity and accretion via Roche lobe overflow. Consequently, the SED would then have to be interpreted as a superposition of emissions from a cold donor and a hot flow component, most likely from an accretion disk. If, on the other hand, the periodicity is super orbital in nature i.e. due to possible interactions of the compact object with a circumstellar disk, the donor could then be a Be/X star hosting a neutron star.

We study the X-ray and optical properties of the ultraluminous X-ray source (ULX) X-6 in the nearby galaxy NGC 4258 (M106) based on the archival XMM-Newton, Chandra, Swift, and Hubble Space Telescope (HST) observations. The source has a peak luminosity of L X ∼ 2 × 10 39 erg sin the XMM-Newton observation of 2004 June. Consideration of the hardness ratios and spectral model parameters shows that the source seems to exhibit possible spectral variations throughout the X-ray observations. In the images from the HST/Advanced Camera for Surveys (ACS), three optical sources have been identified as counterpart candidates within the 1σ error radius of 0 .3. The brightest one has an absolute magnitude of M V ≈ −7.0 and shows extended structure. The remaining two sources have absolute magnitudes of M V ≈ −5.8 and −5.3 mag. The possible spectral types of the candidates from brightest to dimmest were determined as B6−A5, B0−A7, and B2−A3, respectively. The counterparts of the X-ray source possibly belong to a young star cluster. Neither the standard disk model nor the slim disk model provides firm evidence to determine the spectral characteristics of ULX X-6. We argue that the mass of the compact object lies in the range 10 − 15M indicating that the compact source is most likely a stellar-mass black hole.

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We present a detailed study of NGC 6791, NGC 6811, NGC 6819 and NGC 6866, the four open clusters that are located in the Kepler prime field. We use new CCD UBV(RI)KC photometry, which was combined with Gaia EDR3 photometric/astrometric data, to derive the astrophysical parameters with two independent methods - one of them the fitCMD algorithm. Furthermore, we provide among others estimates of the mass and mass function, the cluster structure, derive the cluster orbits, and discuss the cluster dynamics. All objects belong to the older open cluster population (∼1 − 7 Gyr), are in an advanced dynamical stage with signs of mass segregation, and are located close to the solar circle, but show a large range in respect of radii, member stars or observed cluster mass (∼100 − 2000 M⊙). For the three younger objects we were also able to provide photometric metallicity estimates, which confirms their status as clusters with a roughly solar metallicity. The most outstanding object is clearly NGC 6791, a very old cluster with a high metallicity at a distance of about 4.5 kpc from the Sun. We estimate a probable radial migration by about 7 kpc, resulting in a birth position close to the Galactic center.

We present the results of a search for the nature of ultraluminous X-ray source (ULX) X-3 in the nearby galaxy NGC 4258. We use archival data from XMM-Newton, Chandra, NuSTAR and HST observations. Total X-ray data analysed to find the model parameters of the system is indicative of a stellar mass black hole, ∼ 10 M⊙, as the central compact object. Furthermore, analyses of the optical data from HST reveal two optical candidates with the 90 per cent confidence level of error radius of 0${_{.}^{\prime\prime}}$28. Assuming the optical emission is dominated by the donor star, both of these candidates are found to have spectral types that lie between B3−F1 with absolute magnitudes of MV ≈ -6.4. Moreover, the age and mass estimates for the candidates are found to be of 10 and 18 Myr and of 13 and 20 M⊙, respectively.

Astrophysical parameters (age, reddening, distance, radius, luminosity function, mass function, total mass, relaxation time and mass segregation) have been estimated for open clusters NGC 2571, NGC 6802, Koposov 53 and Be 89 by using the Two Micron All Sky Survey(2MASS) photometry. We analyse the color-magnitude diagrams and stellar radial density profiles. We have found that NGC 2571 is the youngest one having young main sequence stars while Be 89 is the oldest cluster.