Development of a Southern Vilnius Standard Photometric System

<p>The Vilnius Standard Photometric System is said to have several advantages over other photometric systems; reduction procedures free of systematic errors, a homogeneous set of standard stars, accurate dereddening, spectral classification and calibration of physical parameters for normal stars, and a good detection rate of abnormal stars. To investigate these, two southern, open star clusters (Omicron Velorum and Kappa Crucis) have been measured in the Vilnius system. The observations were used to derive astrophysical parameters such as age ((45 plus-minus l5)x106 and (10 plus-minus 3)x10 6 years respectively), composition (both solar metallicity), distance to the clusters (m-M = 5m.94 plus-minus 0.02 and 12m.18 plus-minus 0.05), interstellar reddening along our light of sight to the clusters (Ey-v = 0m.00 plus-minus 0.02 and 0m.31 plus-minus 0.09), and cluster membership probabilities for the individual stars. These compared favorably with the consensus of similar analyses made by observers using other photometric systems, with one exception being the distance to Kappa Crucis ( = 11m.59). As no stars further south than declination -26 degrees have been measured in the (original) Vilnius System, it was necessary to calibrate the local system to the standard system by measuring equatorial stars common to both. To alleviate this problem in the future, suitable southern stars were measured to form a southern standard system. Initially bright stars evenly spread across the sky were calibrated - this will ensure any future observing programme will have nearby standards. The next phase of the programme was to calibrate the E-region stars - this is a set of stars in common use as southern standards in other photometric systems. The final phase was to calibrate a sequence of stars near the south celestial pole - producing a set of stars so that the same standards can be observed at any time during the year. This southern standard system could not be completely established in the time available (it is approximately 50% finished), due to the larger than expected uncertainties in the measurements largely caused by the atmospheric effects of the Mount Pinatubo eruption.</p>

Development of a Southern Vilnius Standard Photometric System

<p>The Vilnius Standard Photometric System is said to have several advantages over other photometric systems; reduction procedures free of systematic errors, a homogeneous set of standard stars, accurate dereddening, spectral classification and calibration of physical parameters for normal stars, and a good detection rate of abnormal stars. To investigate these, two southern, open star clusters (Omicron Velorum and Kappa Crucis) have been measured in the Vilnius system. The observations were used to derive astrophysical parameters such as age ((45 plus-minus l5)x106 and (10 plus-minus 3)x10 6 years respectively), composition (both solar metallicity), distance to the clusters (m-M = 5m.94 plus-minus 0.02 and 12m.18 plus-minus 0.05), interstellar reddening along our light of sight to the clusters (Ey-v = 0m.00 plus-minus 0.02 and 0m.31 plus-minus 0.09), and cluster membership probabilities for the individual stars. These compared favorably with the consensus of similar analyses made by observers using other photometric systems, with one exception being the distance to Kappa Crucis ( = 11m.59). As no stars further south than declination -26 degrees have been measured in the (original) Vilnius System, it was necessary to calibrate the local system to the standard system by measuring equatorial stars common to both. To alleviate this problem in the future, suitable southern stars were measured to form a southern standard system. Initially bright stars evenly spread across the sky were calibrated - this will ensure any future observing programme will have nearby standards. The next phase of the programme was to calibrate the E-region stars - this is a set of stars in common use as southern standards in other photometric systems. The final phase was to calibrate a sequence of stars near the south celestial pole - producing a set of stars so that the same standards can be observed at any time during the year. This southern standard system could not be completely established in the time available (it is approximately 50% finished), due to the larger than expected uncertainties in the measurements largely caused by the atmospheric effects of the Mount Pinatubo eruption.</p>

Study of possible regularities of the metallic distribution of open cluster stars according to the LAMOST catalog

In this study were discussed the LAMOST catalog opportunities in the statistical studies of the spectra of stars in open star clusters (OSC). We considered the Pleiades and Praesepe clusters. We examined the absolute stellar magnitude — metallicity relationships for the members of these clusters. Contrary to expectations, a noticeable dependence of the metallicity on the absolute magnitude of the stars in the main sequences of the studied clusters was found, which may be associated with systematic errors in measuring the metallicities for visually faint stars.

Non-stationarity of Open Star Clusters

The monograph poses issues related to the study of the non-stationarity of open star clusters (OSCs), starting with an analysis of the properties of the trajectories of individual stars to the study of collective motion of stars. A discussion of the dynamics of correlations and wave processes in such clusters is presented. The mechanisms of the dynamic evolution of OSCs, the gravitational instability of OSC nuclei, the spectra of frequencies and wavenumbers for oscillations of numerical models of OSCs, astrophysical applications of the results of studies of the dynamics of OSCs are considered. We address the monograph to academic researchers (astronomers and physicists) who are interested in astrophysics, the dynamics of stellar systems, and PhD and senior students of relevant specialities.

Unresolved binaries in open clusters

Проведено исследование популяции двойных звезд в рассеянных звездных скоплениях Галактики с использованием данных космической миссии Европейского космического агентства Gaia. Разработаны две независимые методики определения доли неразрешенных двойных звезд в рассеянных звездных скоплениях. Методики исследованы на моделях скоплений, изучены их возможности и ограничения с учетом особенностей наблюдательных данных. Сделаны оценки доли неразрешенных двойных звезд в скоплениях NGC 2516 и NGC 2447. A study of the binary stars population in open star clusters in the Galaxy was carried out using data from the Gaia space mission of the European Space Agency. Two independent methods have been developed for determining the fraction of unresolved binary stars in open clusters. The techniques were studied on the models of clusters, their capabilities and limitations were studied taking into account the peculiarities of the observational data. The unresolved stars fraction was estimated for the clusters NGC 2516 and NGC 2447.

The star cluster age function in the Galactic disc with Gaia DR2

We perform a systematic reanalysis of the age distribution of Galactic open star clusters. Using a catalogue of homogeneously determined ages for 834 open clusters contained in a 2 kpc cylinder around the Sun and characterised with astrometric and photometric data from the Gaia satellite, we find that it is necessary to revise earlier works that relied on data from the Milky Way Star Cluster survey. After establishing age-dependent completeness limits for our sample, we find that the cluster age function in the range 6.5 < log t < 10 is compatible with Schechter-type or broken power-law functions. Our best-fit values indicate an earlier drop of the age function (by a factor of 2−3) with respect to the results obtained in the last five years, and are instead more compatible with results obtained in the early 2000s along with radio observations of inner-disc clusters. Furthermore, we find a typical destruction timescale of ∼1.5 Gyr for a 104 M⊙ cluster and a present-day cluster formation rate of 0.55−0.15+0.19 Myr−1 kpc−2, suggesting that only 16−8+11% of all stars born in the solar neighbourhood form in bound clusters. Accurate cluster-mass measurements are now needed to place more precise constraints on open-cluster formation and evolution models.