On the distance scale of open clusters

We discuss the state of the distance scale of open clusters in view of various capabilities provided by optical and near-IR observations of galactic objects. Various checks lead to the conclusion that open cluster distance scale requires no appreciable correction. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

On the two-dimensional maps of the distribution of interstellar extinction

A modified version of the method for determining the mean interstellar extinction and constructing the maps of its distribution based on JHK s photometry is proposed. The extinction for each star of the sample is estimated from the Q -index by linearly approximating the line of unreddened stars on the QJHK - (J - H) diagram. The J -band extinction can be calculated by the equation AJ = 2.68 [(J - H) + 0.03 - 1.18 QJHK]. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Planets in triple star systems--the case of HD188753

We consider the formation of the recently discovered ``hot Jupiter'' planet orbiting the primary component of the triple star system HD188753. Although the current outer orbit of the triple is too tight for a Jupiter-like planet to have formed and migrated to its current location, the binary may have been much wider in the past. We assume here that the planetary system formed in an open star cluster, the dynamical evolution of which subsequently led to changes in the system's orbital parameters and binary configuration. We calculate cross sections for various scenarios that could have led to the multiple system currently observed, and conclude that component A of HD188753 with its planet were most likely formed in isolation to be swapped in a triple star system by a dynamical encounter in an open star cluster. We estimate that within 500pc of the Sun there are about 1200 planetary systems which, like Hd188753, have orbital parameters unfavorable for forming planets but still having a planet, making it quite possible that the HD188753 system was indeed formed by a dynamical encounter in an open star cluster.Comment: ApJ Letters in pres

On the metallicity gradient in the Galactic disk

The problem of the chemical composition gradient in the Galactic disk is studied based on a sample of metallicity estimates of open star clusters, using Gaia DR2-improved distance estimates. A clearly non-monotonic variation was observed in the average metallicity of clusters with increasing Galactocentric distance. One can clearly see the metallicity jump of 0.22 in [Fe/H] at a Galactocentric distance of about 9.5 kpc, which appears to be linked to the outer boundary of the thinnest and youngest component of the Galactic disk. The absence of a significant metallicity gradient in the internal (R 10 kpc) regions of the disk demonstrates the absence of noticeable metal enrichment at times of the order of the ages corresponding to those of the disk regions under consideration. Observational data show that the disk experiences noticeable metal enrichment only during the starburst epochs. No significant dependence was identified between the average metallicity and the age of the clusters. © 2020 National Astronomical Observatories, CAS and IOP Publishing Ltd.

The Homogeneous Catalog of the Main Parameters of Open Star Clusters

A brief summary of the updated catalog of homogeneously estimated reddenings, distances from the Sun and ages for 367 open star clusters is given

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

В ходе работы были изучены возможности каталога LAMOST для статистических исследований спектров звезд рассеянных звездных скоплений (РЗС). Были рассмотрены скопления Плеяды и Ясли. Для членов этих скоплений рассмотрены зависимости абсолютная звездная величина — металличность. Вопреки ожиданиям у звезд главных последовательностей исследуемых скоплений обнаружена заметная зависимость металличности от абсолютной звездной величины, которая может быть связана с систематическими ошибками измерения металличностей для визуально слабых звезд.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

Feasibility of an Infrared Parallax Program Using the Fan Mountain Tinsley Reflector

Despite the continuing importance of ground-based parallax measurements, few active programs remain. Because new members of the solar neighborhood tend towards later spectral types, infrared parallax programs are particularly desirable. Consequently, the astrometric quality of the new infrared camera, FanCam, developed by the Virginia Astronomical Instrumentation Laboratory (VAIL) for the 31-in (0.8-m) Tinsley reflector at Fan Mountain Observatory was assessed using 68 J-band exposures of an open cluster, NGC 2420, over a range of hour angles during 2005. Positions of 16 astrometric evaluation stars were measured and the repeatability of those positions was evaluated using the mean error in a single observation of unit weight. Overall, a precision of 1.3 +/- 0.7 microns in x (RA) and 1.3 +/- 0.8 microns in y (Dec) was attained, which corresponds to 0.04" +/- 0.02" in each axis. Although greater precision is expected from CCDs in the visual and near-infrared, this instrument can achieve precision similar to that of the ESO NTT infrared parallax program. Therefore, measuring parallaxes in the infrared would be feasible using this equipment. If initiated, such a program could provide essential distances for brown dwarfs and very low mass stars that would contribute significantly to the solar neighborhood census.Comment: accepted by New Astronomy, minor revisions per refere

Stellar Rotation in Young Clusters. I. Evolution of Projected Rotational Velocity Distributions

Open clusters offer us the means to study stellar properties in samples with well-defined ages and initial chemical composition. Here we present a survey of projected rotational velocities for a large sample of mainly B-type stars in young clusters to study the time evolution of the rotational properties of massive stars. The survey is based upon moderate resolution spectra made with the WIYN 3.5 m and CTIO 4 m telescopes and Hydra multi-object spectrographs, and the target stars are members of 19 young open clusters with an age range of approximately 6 to 73 Myr. We made fits of the observed lines He I 4026, 4387, 4471 and Mg II 4481 using model theoretical profiles to find projected rotational velocities for a total of 496 OB stars. We find that there are fewer slow rotators among the cluster B-type stars relative to nearby B stars in the field. We present evidence consistent with the idea that the more massive B stars (M > 9 solar masses) spin down during their main sequence phase. However, we also find that the rotational velocity distribution appears to show an increase in the numbers of rapid rotators among clusters with ages of 10 Myr and higher. These rapid rotators appear to be distributed between the zero age and terminal age main sequence locations in the Hertzsprung-Russell diagram, and thus only a minority of them can be explained as the result of a spin up at the terminal age main sequence due to core contraction. We suggest instead that some of these rapid rotators may have been spun up through mass transfer in close binary systems.Comment: 33 pages, 11 figures, accepted by Ap

Gaia and Open Clusters

We show the results of our first attempts to use Gaia DR2 data for estimation of the parameters of open clusters using on the base of 42 objects.На примере 42 рассеянных звездных скоплений показаны результаты наших первых попыток использования данных DR2 Gaia при оценивании параметров этих объектов.Работа выполнена при финансовой поддержке государства в лице Министерства науки Российской Федерации (базовая часть госзадания, РК № AAAA-A17-117030310283-7)

On the Metallicity Gradient in the Galaxy

Based on open clusters data, the problem of the metallicity gradient in the galactic disk was studied. A saltatory variation in the average metallicity of clusters with galactocentric distance was obtained. No significant dependence of the average metallicity on the age of the clusters was revealed.По данным о рассеянных звездных скоплениях исследован вопрос о градиенте металличности в диске Галактики. Получено скачкообразное изменение средней металличности скоплений с ростом галактоцентрического расстояния. Не выявлено значимой зависимости средней металличности от возраста скоплений.Работа проведена при финансовой поддержке государства в лице Министерства науки Российской Федерации (базовая часть госзадания, РК № AAAA-A17-117030310283-7), а также при финансовой поддержке Правительства Российской Федерации, постановление № 211, контракт № 02.A03.21.0006