New atlas of open star clusters

Due to numerous new discoveries of open star clusters in the last two decades, astronomers need an easy-to-use resource to get visual information on the relative position of clusters in the sky. Therefore we propose a new atlas of open star clusters. It is based on a table compiled from the largest modern cluster catalogues. The atlas shows the positions and sizes of 3291 clusters and associations, and consists of two parts. The first contains 108 maps of 12 by 12 degrees with an overlapping of 2 degrees in three strips along the Galactic equator. The second one is an online web application, which shows a square field of an arbitrary size, either in equatorial coordinates or in galactic coordinates by request. The atlas is proposed for the sampling of clusters and cluster stars for further investigation. Another use is the identification of clusters among overdensities in stellar density maps or among stellar groups in images of the sky. © 2017 A. F. Seleznev et al.Acknowledgment: The work of Anton F. Seleznev was partly supported by the Ministry of Education and Science (the basic part of the State assignment, RK no. AAAA-A17-117030310283-7). The work of Anton F. Seleznev and of Eka-terina Avvakumova was supported also by the Act no. 211 of the Government of the Russian Federation, agreement no. 02.A03.21.0006. Authors are very grateful to Tatiana Selezneva for the graphic design of the web application

Unresolved Binaries in the Intermediate Mass Range in the Pleiades Star Cluster

The identification of binary stars of different mass ratios in resolved stellar populations is a challenging task. We show how the photometric diagram constructed with the pseudocolors (H-W2)-W1 versus W2-(BP-K) can be employed to estimate the binary and multiple star ratios and the distribution of their component mass ratio q effectively. As an application, we investigate the Pleiades star cluster in the range of primary component mass between 0.5 and 1.8 M ⊙. The binary star ratio is found to be between 0.54 ± 0.11 and 0.70 ± 0.14. On the other hand, the ratio of systems with a multiplicity of more than two is between 0.10 ± 0.00 and 0.14 ± 0.01. The distribution of the component mass ratio q has been approximated by a power law with the exponent between -0.53 ± 0.10 and -0.63 ± 0.22. Below 0.5 M ⊙, we expect a large number of brown dwarfs among secondary components. © 2022. The Author(s). Published by the American Astronomical Society.The work of A.F.S. was supported by the Ministry of Science and Higher Education of the Russian Federation, FEUZ-2020-0030. The work of G.C. was supported by Padova University grant BIRD191235/19: Internal dynamics of Galactic star clusters in the Gaia era: binaries, blue stragglers, and their effect in estimating dynamical masses

On the Motion of Stars in the Pleiades According to Gaia DR2 Data

Abstract—Several parameters of the Pleiades cluster were estimated. We used Gaia DR2 data on the coordinates, proper motions, and radial velocities of stars in regions with radius d° =2.5° and size 60° × 60° around the cluster center. Based on data on stars with magnitudes mG ≤ 18m, we constructed a map and profile of the density, luminosity and mass functions of the cluster, determined the cluster radius, 10.9° ± 0.3° (26.3 ± 0.7 pc), and the radius of its core, 2.62° (6.24 pc), and obtained estimates for the number of stars in the cluster, 1542 ± 121, and their mass, 855 ± 104M⊙; numbers of stars in the core of the cluster, 1097 ± 77, and their mass 665 ± 71M⊙. Distribution of stars with mG< 16m at distances rs from the cluster center in three-dimensional space of rs< 1 pc and at rs ∼ 1.4–5 pc contains radial density waves. Based on the data on stars with mG< 16m, we determined the average rotation velocity of the core of the cluster vc = 0.56 ± 0.07 km s−1 at distances d in the sky plane d ≤ 4.6 pc from its center. The rotation is “prograde”, the angle between the projection of the axis of rotation of the cluster core onto the sky plane and the direction to the North Pole of the Galaxy is ϕ = 18.8° ± 4.4°, the angle between the axis of rotation of the cluster core and the sky plane is ϑ = 43.2° ± 4.9°, the rotation velocity of the cluster core at a distance of d ≃ 5.5pc from its center is close to zero: vc = 0.1 ± 0.3 km s−1. According to the data on stars with mG< 17m, the velocity of the “retrograde” rotation of the cluster at a distance of d ≃ 7.1 pc from its center is vc = 0.48 ± 0.20 km s−1, the angle ϕ = 37.8° ± 26.4°. The dependences of moduli of the tangential and radial components of the velocity field of the stars of the cluster core in the sky plane on the distance d to the center of the cluster contain a number of periodic oscillations. The dispersions of the velocities of the stars in the cluster core σv increase on average with an increase in rs, which, like the radial density waves and the waves of oscillations of the velocity field in the sky plane, indicates the nonstationarity of the cluster in the field of regular forces. The Jeans wavelength in the cluster core decreases, and the velocity dispersion of the stars in the core under the Jeans instability increases after taking into account the influence of the external field of the Galaxy on the cluster. The region of gravitational instability in the Pleiades cluster is located in the interval rs = 2.2–5.7 pc and contains 39.4–60.5% of the total number of stars in the considered samples of cluster stars. Estimates of the Pleiades dynamic mass and tidal radius are obtained. © 2020, Pleiades Publishing, Ltd.The authors are grateful to A. A. Popov, a researcher at the Astronomical Observatory of the Ural Federal University, who pointed out the possibility of the influence of the OSC motion, perpendicular to the line of sight, on the radial velocities of the cluster stars. This work used data from the European Space Agency (ESA) Gaia mission (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for DPAC was provided by national institutions, in particular institutions participating in the Gaia multilateral agreement

Luminosity and mass function of galactic open clusters: I. NGC 4815

We present deep V and I photometry for the open cluster NGC 4815 and four surrounding Galactic fields down to a limiting magnitude $V\sim25$. These data are used to study cluster spatial extension by means of star counts, and to derive the luminosity (LF) and mass function (MF). The radius turns out to be $3.6\pm0.3 arcmin$ at V=19.0 level, whereas the mass amounts at $880\pm230 m_{\odot}$ down to V=20.8. From the color-magnitude diagram, we obtain the LFs in the V and I bands, using both the standard histogram and an adaptive kernel. After correction for incompleteness and field star contamination, the LFs have been transformed into the present day mass functions (PDMF). The PDMFs from the V and I photometry can be represented as a power-law with a slope $\alpha = 3.1\pm0.3$ and $\alpha = 2.9\pm0.3$ (the \cite{salp55} MF in this notation has a slope $\alpha = 2.35$) respectively, in the mass range $2.5 \leq \frac{m}{m_{\odot}} \leq 0.8$. Below this mass, the MF cannot be considered as representative of the cluster IMF, as it is the result of the combined effect of strong irregularities in the stellar background, probable internal dynamical evolution of the cluster and/or interaction of the cluster with the dense Galactic field. Unresolved binaries and mass segregation can only flatten the apparent derived IMF, so we expect that the real IMF must be steeper than the quoted slope by an unknown amount.Comment: 12 pages, 10 eps figures, in press in Astronomy and Astrophysic

Star formation around the H II region Sh2-235

We present a picture of star formation around the H ii region Sh2-235 (S235) based upon data on the spatial distribution of young stellar clusters and the distribution and kinematics of molecular gas around S235. We observed 13CO (1-0) and CS (2-1) emission toward S235 with the Onsala Space Observatory 20-m telescope and analysed the star density distribution with archival data from the Two Micron All-Sky Survey (2MASS). Dense molecular gas forms a shell-like structure at the southeastern part of S235. The young clusters found with 2MASS data are embedded in this shell. The positional relationship of the clusters, the molecular shell and the H ii region indicates that expansion of S235 is responsible for the formation of the clusters. The gas distribution in the S235 molecular complex is clumpy, which hampers interpretation exclusively on the basis of the morphology of the star-forming region. We use data on kinematics of molecular gas to support the hypothesis of induced star formation, and distinguish three basic types of molecular gas components. The first type is primordial undisturbed gas of the giant molecular cloud, the second type is gas entrained in motion by expansion of the H ii region (this is where the embedded clusters were formed) and the third type is a fast-moving gas, which might have been accelerated by winds from the newly formed clusters. The clumpy distribution of molecular gas and its kinematics around the H ii region implies that the picture of triggered star formation around S235 can be a mixture of at least two possibilities: the 'collect-and-collapse' scenario and the compression of pre-existing dense clumps by the shock wave. Journal compilation © 2008 RAS

Star formation around the H II region Sh2-235

We present a picture of star formation around the H ii region Sh2-235 (S235) based upon data on the spatial distribution of young stellar clusters and the distribution and kinematics of molecular gas around S235. We observed 13CO (1-0) and CS (2-1) emission toward S235 with the Onsala Space Observatory 20-m telescope and analysed the star density distribution with archival data from the Two Micron All-Sky Survey (2MASS). Dense molecular gas forms a shell-like structure at the southeastern part of S235. The young clusters found with 2MASS data are embedded in this shell. The positional relationship of the clusters, the molecular shell and the H ii region indicates that expansion of S235 is responsible for the formation of the clusters. The gas distribution in the S235 molecular complex is clumpy, which hampers interpretation exclusively on the basis of the morphology of the star-forming region. We use data on kinematics of molecular gas to support the hypothesis of induced star formation, and distinguish three basic types of molecular gas components. The first type is primordial undisturbed gas of the giant molecular cloud, the second type is gas entrained in motion by expansion of the H ii region (this is where the embedded clusters were formed) and the third type is a fast-moving gas, which might have been accelerated by winds from the newly formed clusters. The clumpy distribution of molecular gas and its kinematics around the H ii region implies that the picture of triggered star formation around S235 can be a mixture of at least two possibilities: the 'collect-and-collapse' scenario and the compression of pre-existing dense clumps by the shock wave. Journal compilation © 2008 RAS

Consideration of unresolved binaries with evaluation of the mass of star clusters

При различных предположениях о функции масс компонент двойных систем оценивается, как наличие неразрешенных двойных систем влияет на определение массы скопления.An influence of the presence of unresolved binaries onto star cluster mass estimation is evaluated with different assumptions on the mass function of binary components.Часть работ проведена при финансовой поддержке государства в лице Министерства образования и науки Российской Федерации (базовая часть госзадания, РК №AAAA-A17-117030310283-7), а также при финансовой поддержке Правительства РФ (постановление № 211, контракт № 02.A03.21.0006)

Comparative Analysis of the Dynamical Spectra of a Polarization of an Active Medium and an Electromagnetic Field in the Superradiant Heterolasers

The complicated pulsed generation regimes of a CW-pumped superradiant semiconductor laser are analyzed via the dynamical spectra of the dipole optical oscillations of active centers. This novel approach appears to be more informative than the standard analysis of the dynamical spectra of laser emission if a dipole relaxation rate is less than a cavity relaxation rate. The advantages of the method are demonstrated for a number of superradiant lasing regimes on the basis of the numerical solution to 1D Maxwell–Bloch equations for a two-level active medium in a low-Q cavity within one-dimensional approximation

Superconducting parallel nanowire detector with photon number resolving functionality

We present a new photon number resolving detector (PNR), the Parallel Nanowire Detector (PND), which uses spatial multiplexing on a subwavelength scale to provide a single electrical output proportional to the photon number. The basic structure of the PND is the parallel connection of several NbN superconducting nanowires (100 nm-wide, few nm-thick), folded in a meander pattern. Electrical and optical equivalents of the device were developed in order to gain insight on its working principle. PNDs were fabricated on 3-4 nm thick NbN films grown on sapphire (substrate temperature TS=900C) or MgO (TS=400C) substrates by reactive magnetron sputtering in an Ar/N2 gas mixture. The device performance was characterized in terms of speed and sensitivity. The photoresponse shows a full width at half maximum (FWHM) as low as 660ps. PNDs showed counting performance at 80 MHz repetition rate. Building the histograms of the photoresponse peak, no multiplication noise buildup is observable and a one photon quantum efficiency can be estimated to be QE=3% (at 700 nm wavelength and 4.2 K temperature). The PND significantly outperforms existing PNR detectors in terms of simplicity, sensitivity, speed, and multiplication noise

Study of Clusters in the Star-Forming Region G174+2.5

В работе исследуются широкие окрестности области G174+2.5, которые включают как известные погруженные скопления, так и кандидаты в скопления. Последний релиз UKIDSS позволяет обнаруживать звезды до 17—18 звездной величины, что дает возможность дополнить перепись звезд скоплений. В работе определяются астрофизические параметры скоплений (центры, радиусы, количество звезд, покраснение). Для четырех областей дополнительно определены вероятности принадлежности звезд к скоплениям, оценены расстояния до скоплений и исследована их кинематика с использованием данных Gaia EDR3.We study the wide vicinity of the G174+2.5 region, which includes both known embedded clusters and cluster candidates. The latest release of UKIDSS makes it possible to detect stars up to 17—18 magnitudes, which allows to supplement the list of the cluster’s stars. Astrophysical parameters of clusters (centers, radii, number of stars, reddening) are determined in the work. For 4 regions, the star membership probabilities in clusters were additionally determined, distances to clusters were estimated, and their kinematics was studied using Gaia EDR3 data.Работа выполнена при финансовой поддержке Министерства науки и высшего образования Российской Федерации, тема FEUZ-2023-0019