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1
Torres, C. A. O., G. R. Quast, C. H. F. Melo, M. Sterzik, R. de la Reza et Licio da Silva. « sacy : open clusters connected to young nearby associations ». Proceedings of the International Astronomical Union 5, S266 (août 2009) : 544. http://dx.doi.org/10.1017/s1743921309992018.
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AbstractIn recent years. we have spectroscopically observed thousands of counterparts of selected ROSAT bright sources in the sacy project (Search for Associations Containing Young stars). We demonstrated that hundreds of the young stars found this way belong to nearby young, loose associations, some detected only in sacy, with ages in the range from 5 to 100 Myr. For their ages, these associations show no trace of their primitive nurseries, which poses some difficulties as to their origins. Nevertheless, there are some associations clearly associated with young open clusters, such as the ϵ Cha association (6 Myr) with the η Cha cluster, and the Argus association with IC 2391 (40 Myr). There seem to exist also more subtle connections, such as the AB Dor association (75 Myr) with the Pleiades. Here, we present evidence of the connections of young associations to open clusters, to understand their origin and their possible insertion in the cluster infant-mortality and Gould Belt scenarios.
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Freeman, K. C., D. C. Heggie, G. L. H. Harris, G. Lynga, P. E. Nissen, C. Pilachowski et G. N. Salufcvadze. « Commission 37 : Star Clusters and Associations ». Transactions of the International Astronomical Union 19, no 1 (1985) : 521–45. http://dx.doi.org/10.1017/s0251107x0000660x.
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The last three years have been very productive for cluster research. This report, on activities in the field, has been compiled by the members of Commission 37. It begins with sections on recent meetings, and on data catalogs (G. Lynga). Detailed tables of work on associations (P.E. Nissen), open clusters (G.L.H. Harris) and globular clusters (R.E. White) are then given. A section on cluster dynamics (D.C. Heggie) follows, and the final section concerns present trends in cluster research (C. Pilachowski).
3
Medina, Gustavo E., Bertrand Lemasle et Eva K. Grebel. « A revisited study of Cepheids in open clusters in the Gaia era ». Monthly Notices of the Royal Astronomical Society 505, no 1 (4 mai 2021) : 1342–66. http://dx.doi.org/10.1093/mnras/stab1267.
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ABSTRACT In this paper, we revisit the problem of identifying bona fide cluster Cepheids by performing an all-sky search for Cepheids associated with open clusters and making use of state-of-the-art catalogued information for both Cepheids and clusters, based on the unparalleled astrometric precision of the second and early third data releases of the Gaia satellite. We determine membership probabilities by following a Bayesian approach using spatial and kinematic information of the potential cluster-Cepheid pairs. We confirm 19 Cepheid-cluster associations considered in previous studies as bona fide, and question the established cluster membership of six other associations. In addition, we identify 138 cluster Cepheid candidates of potential interest, mostly in recently discovered open clusters. We report on at least two new clusters possibly hosting more than one Cepheid. Furthermore, we explore the feasibility of using open clusters hosting Cepheids to empirically determine the Cepheid period–age relation through the use of Gaia and 2MASS photometry and a semiautomated method to derive cluster ages. We conclude that the usage of cluster Cepheids as tentative probes of the period–age relations still faces difficulties due to the sparsely populated red giant branch and the stochastically sampled main-sequence turn-off of the open clusters, making age determinations a challenging task. This biases the age-datable cluster selection for Cepheid period-age studies towards older and high-mass clusters.
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Deacon, N. R., et A. L. Kraus. « Wide binaries are rare in open clusters ». Monthly Notices of the Royal Astronomical Society 496, no 4 (30 juin 2020) : 5176–200. http://dx.doi.org/10.1093/mnras/staa1877.
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ABSTRACT The population statistics of binary stars are an important output of star formation models. However, populations of wide binaries evolve over time due to interactions within a system’s birth environment and the unfolding of wide, hierarchical triple systems. Hence, the wide binary populations observed in star-forming regions or OB associations may not accurately reflect the wide binary populations that will eventually reach the field. We use Gaia DR2 data to select members of three open clusters, Alpha Per, the Pleiades, and Praesepe and to flag cluster members that are likely unresolved binaries due to overluminosity or elevated astrometric noise. We then identify the resolved wide binary population in each cluster, separating it from coincident pairings of unrelated cluster members. We find that these clusters have an average wide binary fraction in the 300–3000 au projected separation range of 2.1$\pm ^{0.4}_{0.2}$ per cent increasing to 3.0$\pm ^{0.8}_{0.7}$ per cent for primaries with masses in the 0.5–1.5 M⊙ range. This is significantly below the observed field wide binary fraction, but shows some wide binaries survive in these dynamically highly processed environments. We compare our results with another open cluster (the Hyades) and two populations of young stars that likely originated in looser associations (young moving groups and the Pisces-Eridanus stream). We find that the Hyades also has a deficit of wide binaries while the products of looser associations have wide binary fractions at or above field level.
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Zinnecker, Hans. « Embedded and open star clusters : basic questions ». Proceedings of the International Astronomical Union 5, S266 (août 2009) : 17–23. http://dx.doi.org/10.1017/s1743921309990810.
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AbstractThis paper provides an introduction to IAU Symposium 266 on star clusters as basic building blocks in space and time. We define clusters as bound systems and discriminate them from general stellar clusterings or groups and unbound associations. We give a few examples of young, embedded, compact clusters which may evolve into looser, open clusters after dynamical relaxation due to mass loss and secular relaxation processes. We ask how and where star clusters form (in normal and interacting galaxies) and provide statistics of open clusters in terms of cluster masses and ages in the solar neighborhood (where observational data are most complete). Finally, we list a number of basic questions for current and future star cluster research and discuss the prospects for cluster studies with the next generation infrared and submillimeter telescopes (Herschel; JWST, E–ELT; ALMA, NOEMA).
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Heggie, D. C., G. L. H. Harris, K. C. Freeman, J. E. Hesser, P. E. Nissen, C. Pilachowski et G. N. Salukvadze. « Commission 37 : Star Clusters and Associations (Amas Stellaires Et Associations) ». Transactions of the International Astronomical Union 20, no 01 (1988) : 509–35. http://dx.doi.org/10.1017/s0251107x00007355.
Texte intégralRésumé :
The last three years have been very productive for cluster research, especially now that observations with CCDs have become so routine. After a section on recent meetings, and one on data catalogues (by J.-C. Mermilliod), subsequent sections of this report go into details on individual topics: associations (P.E. Nissen), open clusters (G.L.H. Harris), globular clusters and cluster systems (R.E. White) and dynamical theory (D.C. Heggie).The rapid growth in the volume of observational data has meant regrettably that the information has had to be tabulated in an even more compressed form than in earlier Reports. As in previous Reports, three-figure references are to Astronomy and Astrophysics Abstracts, and two-figure references to Physics Abstracts. Most entries cover publications from 1 July 1984 to 30 June 1987, but some exceptions are noted under the individual sections. For abbreviations see §6.
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Fragkou, Vasiliki, Quentin A. Parker, Albert A. Zijlstra, Roberto Vázquez, Laurence Sabin et Jackeline Suzett Rechy-Garcia. « The Planetary Nebula in the 500 Myr Old Open Cluster M37 ». Astrophysical Journal Letters 935, no 2 (1 août 2022) : L35. http://dx.doi.org/10.3847/2041-8213/ac88c1.
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Abstract We report confirmation of a large, evolved, bipolar planetary nebula and its blue, white dwarf central star as a member of the ∼500 Myr old Galactic open star cluster M37 (NGC 2099). This is only the third known example of a planetary nebula in a Galactic open cluster and was found via our ongoing program of identifying and studying planetary nebulae—open cluster associations. High confidence in the association comes from the consistent radial velocities and proper motions for the confirmed central star and cluster stars from Gaia, reddening agreement, and location of the planetary nebula well within the tidal cluster boundary. Interestingly, all three Galactic examples have bipolar morphology and likely Type-I chemistry, both characteristics of higher mass progenitors. In this case the progenitor star mass is in the midrange of ∼2.8 M ☉. It provides a valuable, additional point on the key stellar initial-to-final mass relation independent of cluster white dwarf estimates and also falls in a gap in the poorly sampled mass region. This planetary nebula also appears to have the largest kinematical age ever determined and implies increased visibility lifetimes when they are located in clusters.
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Schneider, H. « CP3 Stars in Open Clusters ». International Astronomical Union Colloquium 138 (1993) : 639–43. http://dx.doi.org/10.1017/s0252921100021138.
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AbstractAbt published in 1979 frequencies of peculiar stars in open clusters based on published classifications for 661 stars in 14 open clusters and associations. Among others he discussed an age dependence of the frequencies of CP3 stars and found them increasing with age. Furthermore, he suggested a possible age dependence of the rotational velocity of these stars.But the sample he used was rather small: he found eight CP3 stars in 5 open clusters. In the mean time the number of cluster CP3 stars was more than double. Therefore, the findings of Abt shall be examined on the basis of the larger sample.
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Prišegen, M., M. Piecka, N. Faltová, M. Kajan et E. Paunzen. « White dwarf-open cluster associations based on Gaia DR2 ». Astronomy & ; Astrophysics 645 (21 décembre 2020) : A13. http://dx.doi.org/10.1051/0004-6361/202039276.
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Context. Fundamental parameters and physical processes leading to the formation of white dwarfs (WDs) may be constrained and refined by discovering WDs in open clusters (OCs). Cluster membership can be utilized to establish the precise distances, luminosities, ages, and progenitor masses of such WDs. Aims. We compile a list of probable WDs that are OC members in order to facilitate WD studies that are impractical or difficult to conduct for Galactic field WDs. Methods. We use recent catalogs of WDs and OCs that are based on the second data release of the Gaia satellite mission (GDR2) to identify WDs that are OC members. This crossmatch is facilitated by the astrometric and photometric data contained in GDR2 and the derived catalogs. Assuming that most of the WD members are of the DA type, we estimate the WD masses, cooling ages, and progenitor masses. Results. We have detected several new likely WD members and reassessed the membership of the literature WDs that had been previously associated with the studied OCs. Several of the recovered WDs fall into the recently reported discontinuity in the initial-final mass relation (IFMR) around Mi ∼ 2.0 M⊙, which allows for tighter constrains on the IFMR in this regime.
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Dinnbier, František, Pavel Kroupa, Ladislav Šubr et Tereza Jeřábková. « Estimating the Ages of Open Star Clusters from Properties of Their Extended Tidal Tails ». Astrophysical Journal 925, no 2 (1 février 2022) : 214. http://dx.doi.org/10.3847/1538-4357/ac400e.
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Abstract The most accurate current methods for determining the ages of open star clusters, stellar associations, and stellar streams are based on isochrone fitting or the lithium depletion boundary. We propose another method for dating these objects based on the morphology of their extended tidal tails, which have been recently discovered around several open star clusters. Assuming that the tidal tails originate from the stars released from the cluster during early gas expulsion, or that they form in the same star-forming region as the cluster (i.e., being coeval with the cluster), we derive the analytical formula for the tilt angle β between the long axis of the tidal tail and the orbital direction for clusters or streams on circular trajectories. Since at a given Galactocentric radius β is only a function of age t regardless of the initial properties of the cluster, we estimate the cluster age by inverting the analytical formula β = β(t). We illustrate the method on a sample of 12 objects, which we compiled from the literature, and we find a reasonable agreement with previous dating methods in ≈70% of the cases. This can probably be improved by taking into account the eccentricity of the orbits and by revisiting the dating methods based on stellar evolution. The proposed morphological method is suitable for relatively young clusters (age ≲300 Myr), where it provides a relative age error of the order of 10%−20% for an error in the observed tilt angle of 5°.
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Grebel, Eva K. « Star Clusters in Irregular Galaxies in the Local Group ». Symposium - International Astronomical Union 207 (2002) : 94–104. http://dx.doi.org/10.1017/s0074180900223425.
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I summarize our knowledge of star clusters and associations in irregular galaxies other than the Magellanic Clouds in the Local Group. Surveys affording complete area coverage at high angular resolution are still lacking. Confirmed globular clusters are known only in NGC 6822 and WLM. Very few dIrrs contain populous or sparse open clusters. There is a pronounced deficiency of intermediate-age and young clusters. Apart from parent galaxy mass, the lack of interactions may be a key reason for the lack of cluster formation in the dIrrs. All dIrrs have one or several short-lived OB associations in the star-forming regions in their centers.
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Straižys, V., R. P. Boyle, K. Milašius, K. Černis, M. Macijauskas, U. Munari, R. Janusz et al. « Young open cluster IC 4996 and its vicinity : multicolor photometry and Gaia DR2 astrometry ». Astronomy & ; Astrophysics 623 (26 février 2019) : A22. http://dx.doi.org/10.1051/0004-6361/201833987.
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The open cluster IC 4996 in Cygnus and its vicinity are investigated by applying a two-dimensional photometric classification of stars measured in the Vilnius seven-color photometric system. Cluster members are identified by applying distances based on the Gaia DR2 parallaxes and the point vector diagram of the Gaia DR2 proper motions. For some B-type stars, spectroscopic MK types are also obtained from the Asiago spectra and collected from the literature. New parameters of the cluster are derived. The interstellar extinction AV covers a wide range of values, from 1.3 to 2.4 mag; the mean value in the central part of the cluster is 1.8 mag. The cluster distance is 1915 ± 110 pc, and its age is within 8–10 Myr. The cluster exhibits a long sequence from early-B to G stars, where stars cooler than B8 are in the pre-main-sequence stage. The plot of extinction versus distance shows a steep rise of AV up to 1.6 mag at 700–800 pc, which is probably related to dust clouds at the edge of the Great Cygnus Rift. The next increase in extinction by an additional 0.8 mag at d ≥ 1.7 kpc is probably related to the associations Cyg OB1 and Cyg OB3. The cluster IC 4996 does not belong to the Cyg OB1 association, which is located closer to the Sun, at 1682 ± 116 pc. It seems likely that the cluster and the surrounding O-B stars have a common origin with the nearby association Cyg OB3 since Gaia data show that these stellar groups are located at a similar distance.
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Vančová, Viera, Miloš Čambál et Dagmar Cagáňová. « Innovative Improvement and Intensification of Business Relationships Supported by Cooperative Networks ». Research Papers Faculty of Materials Science and Technology Slovak University of Technology 20, Special-Number (1 décembre 2012) : 137–42. http://dx.doi.org/10.2478/v10186-012-0024-3.
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Abstract Nowadays, the opportunity for companies to be involved in cluster initiatives and international business associations is a major factor that contributes to the increase of their innovative potential. Companies organized in technological clusters have greater access to mutual business contacts, faster information transfer and deployment of advanced technologies. These companies cooperate more frequently with universities and research - development institutions on innovative projects. An important benefit of cluster associations is that they create a suitable environment for innovation and the transfer of knowledge by means of international cooperation and networking. This supportive environment is not easy to access for different small and mediumsized companies, who are not members of any clusters or networks. Supplier-customer business channels expand by means of transnational networks and exchanges of experience. Knowledge potential is broadened and joint innovative projects are developed. Reflecting the growing importance of clusters as driving forces of economic and regional development, a number of cluster policies and initiatives have emerged in the last few decades, oriented to encourage the establishment of new clusters, to support existing clusters, or to assist the development of transnational cooperation. To achieve the goals of the Europe 2020 Strategy, European countries should have an interest in building strong clusters and developing cluster cooperation by sharing specialized research infrastructures and testing facilities and facilitating knowledge transfer for crossborder cooperation. This requires developing a long term joint strategy in order to facilitate the development of open global clusters and innovative small and medium entrepreneurs.
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Chentsov, E. L., E. G. Sendzikas et M. V. Yushkin. « Open Cluster NGC6613 in SerOB1 A Association ». Astrophysical Bulletin 73, no 4 (octobre 2018) : 430–36. http://dx.doi.org/10.1134/s1990341318040053.
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Wramdemark, S., G. Lyngå et L. E. B. Johansson. « CO and CS Observations in the Eastern Part of W5 ». Symposium - International Astronomical Union 115 (1987) : 211–12. http://dx.doi.org/10.1017/s0074180900095590.
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At galactic longitudes between 132 and 139 degrees and distances of 2 to 2.5 kpc, the galactic disk contains an unusual concentration of gas clouds, young clusters and OB associations (W3, W4 and W5). The small nebula S 201 is situated to the east of W5, which contains the young open cluster IC 1848. Probably associated with S 201 is one of the originally proposed Bok globules; the region also contains three infrared sources.
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Carraro, Giovanni, Richard de Grijs, Bruce Elmegreen, Peter Stetson, Barbara Anthony-Twarog, Simon Goodwin, Douglas Geisler et Dante Minniti. « HIGHLIGHTS OF COMMISSION 37 SCIENCE RESULTS ». Proceedings of the International Astronomical Union 11, T29A (août 2015) : 502–21. http://dx.doi.org/10.1017/s174392131600096x.
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AbstractIt is widely accepted that stars do not form in isolation but result from the fragmentation of molecular clouds, which in turn leads to star cluster formation. Over time, clusters dissolve or are destroyed by interactions with molecular clouds or tidal stripping, and their members become part of the general field population. Star clusters are thus among the basic building blocks of galaxies. In turn, star cluster populations, from young associations and open clusters to old globulars, are powerful tracers of the formation, assembly, and evolutionary history of their parent galaxies. Although their importance (e.g., in mapping out the Milky Way) had been recognised for decades, major progress in this area has only become possible in recent years, both for Galactic and extragalactic cluster populations. Star clusters are the observational foundation for stellar astrophysics and evolution, provide essential tracers of galactic structure, and are unique stellar dynamical environments. Star formation, stellar structure, stellar evolution, and stellar nucleosynthesis continue to benefit and improve tremendously from the study of these systems. Additionally, fundamental quantities such as the initial mass function can be successfully derived from modelling either the Hertzsprung-Russell diagrams or the integrated velocity structures of, respectively, resolved and unresolved clusters and cluster populations. Star cluster studies thus span the fields of Galactic and extragalactic astrophysics, while heavily affecting our detailed understanding of the process of star formation in dense environments. This report highlights science results of the last decade in the major fields covered by IAU Commission 37: Star clusters and associations. Instead of focusing on the business meeting - the out-going president presentation can be found here:http://www.sc.eso.org/gcarraro/splinter2015.pdf- this legacy report contains highlights of the most important scientific achievements in the Commission science area, compiled by 5 well expert members.
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Terrell, Dirk, John Gross et Walter Cooney. « Analysis of the Open Cluster NGC 2281 ». Galaxies 9, no 1 (21 janvier 2021) : 7. http://dx.doi.org/10.3390/galaxies9010007.
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BV observations of an approximately 68′×48′ field centered on the open cluster NGC 2281 and covering more than 400 nights from 2013 to 2018 are presented. The photometric observations were transformed to the standard system using standards from the American Association of Variable Star Observers Photometric All-sky Survey (APASS) DR10 and analyzed with Gaia DR2 parallaxes and proper motions to determine the distance, age, and metallicity of the cluster. The discovery of an eclipsing binary in the field is discussed.
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DARLING, N. D., D. E. POSS, M. P. SCHOELEN, M. METCALF-KELLY, S. E. HILL et S. HARRIS. « Retrospective, epidemiological cluster analysis of the Middle East respiratory syndrome coronavirus (MERS-CoV) epidemic using open source data ». Epidemiology and Infection 145, no 15 (24 octobre 2017) : 3106–14. http://dx.doi.org/10.1017/s0950268817002345.
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SUMMARYThe Middle East respiratory syndrome coronavirus (MERS-CoV) is caused by a novel coronavirus discovered in 2012. Since then, 1806 cases, including 564 deaths, have been reported by the Kingdom of Saudi Arabia (KSA) and affected countries as of 1 June 2016. Previous literature attributed increases in MERS-CoV transmission to camel breeding season as camels are likely the reservoir for the virus. However, this literature review and subsequent analysis indicate a lack of seasonality. A retrospective, epidemiological cluster analysis was conducted to investigate increases in MERS-CoV transmission and reports of household and nosocomial clusters. Cases were verified and associations between cases were substantiated through an extensive literature review and the Armed Forces Health Surveillance Branch's Tiered Source Classification System. A total of 51 clusters were identified, primarily nosocomial (80·4%) and most occurred in KSA (45·1%). Clusters corresponded temporally with the majority of periods of greatest incidence, suggesting a strong correlation between nosocomial transmission and notable increases in cases.
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Moraux, E. « Open clusters and associations in the Gaia era ». EAS Publications Series 80-81 (2016) : 73–114. http://dx.doi.org/10.1051/eas/1680004.
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Prokeš, Martin, et Pavel Tomšík. « Increasing competitiveness of wine producers in strategic alliances VOC ». Acta Universitatis Agriculturae et Silviculturae Mendelianae Brunensis 60, no 2 (2012) : 293–98. http://dx.doi.org/10.11118/actaun201260020293.
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The paper describes the main reasons for the formation of new regional association of wineries, based on a different origin for wines in the wine region of Moravia in the southeast part of the Czech Republic. This research aim is to create a plan for new development of such strategic alliances on the basis of results of localization factors. There coefficient of localization is used for identification of cluster. Results are compared with already operating on associations for the appellation in Austria DAC. They were traced changes in consumer preferences in the Czech wine market. Consumers are placing more emphasis on the selection of wine on its descent from a particular area, growing community and the individual grower. This paper specifically introduces new associations for appellation system VOC. This alliance is described in the context of the establishment, operation, development and expansion, respectively the possibility of involvement of additional organizations suppliers and research institutions. The application of the results of research was a plan for the establishment of new alliance VOC Modré Hory, where are associated 30 wine producers of wine in 5 villages around the center Velké Pavlovice. Based on the experience of newly emerging VOC system of appellations was setting up a plan of formation association with the proposed methodological approach. Open cooperation between associations VOC appellation and other entities involving suppliers, customers, research institutions and universities has the possibility of creating an institutionalized wine cluster. The plan to create a wine cluster was proposed to establish cooperation between the newly emerging associations of VOC at three sub-regions of South Moravia, in order to achieve competitive advantage.
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Fragkou, Vasiliki, Quentin A. Parker, Albert A. Zijlstra, Lisa Crause, Laurence Sabin et Roberto Vázquez. « Further Studies of the Association of Planetary Nebula BMP J16135406 with Galactic Open Cluster NGC 6067 ». Galaxies 10, no 2 (7 mars 2022) : 44. http://dx.doi.org/10.3390/galaxies10020044.
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Planetary Nebulae (PNe) that are physical members of Galactic open clusters are powerful probes that allow precise determination of their distance and crucially their initial mass on the main sequence. Here, we revisit the physical association of the PN BMP J1613–5406 with the open cluster NGC 6067 and present our preliminary results based on our new ESO/VLT FORS2 data. Our PN spectral data permit the calculation of a precise radial velocity and reddening to the PN that shows a tight consistency with the literature corresponding cluster parameters including importantly the radial velocity. Our measurements, combined with the agreement between the distances of the two objects and the fact that the PN is located well within the cluster boundaries, confirm that the PN is physically associated with the cluster. The cluster has a turn-off mass of around 5 solar masses that indicates a PN initial mass of around 5.6 solar masses. This is closer to the theoretical lower limit of core-collapse supernova formation than has ever been previously observed, providing a unique opportunity for further stellar and Galactic chemical evolution studies using this system.
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Negueruela, I., C. González-Fernández, A. Marco et J. S. Clark. « A massive association around the obscured open cluster RSGC3 ». Astronomy & ; Astrophysics 528 (1 mars 2011) : A59. http://dx.doi.org/10.1051/0004-6361/201016102.
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Bragaglia, A., E. J. Alfaro, E. Flaccomio, R. Blomme, P. Donati, M. Costado, F. Damiani et al. « The Gaia-ESO Survey : Target selection of open cluster stars ». Astronomy & ; Astrophysics 659 (mars 2022) : A200. http://dx.doi.org/10.1051/0004-6361/202142674.
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Context. The Gaia-ESO Survey (GES) is a public, high-resolution spectroscopic survey, conducted with the multi-object spectrograph Fibre Large Array Multi Element Spectrograph (FLAMES) on the Very Large Telescope (European Southern Observatory, ESO, Cerro Paranal, Chile) from December 2011 to January 2018. Gaia-ESO has targeted all the main stellar components of the Milky Way, including thin and thick disc, bulge, and halo. In particular, a large sample of open clusters has been observed, from very young ones, just out of the embedded phase, to very old ones. Aims. The different kinds of clusters and stars targeted in them are useful to reach the main science goals of the open cluster part of GES, which are the study of the open cluster structure and dynamics, the use of open clusters to constrain and improve stellar evolution models, and the definition of Galactic disc properties (e.g., metallicity distribution). Methods. The Gaia-ESO Survey is organised in 19 working groups (WGs), each one being responsible for a task. We describe here the work of three of them, one in charge of the selection of the targets within each cluster or association (WG4), one responsible for defining the most probable candidate member stars (WG1), and another one in charge of the preparation of the observations (WG6). As the entire GES has been conducted before the second Gaia data release, we could not make use of the Gaia astrometry to define cluster member candidates. We made use of public and private photometry to select the stars to be observed with FLAMES, once brought on a common astrometric system (the one defined by 2MASS). Candidate target selection was based on ground-based proper motions, radial velocities, and X-ray properties when appropriate, for example, and it was mostly used to define the position of the clusters’ evolutionary sequences in the colour-magnitude diagrams. Targets for GIRAFFE were then selected near the sequences in an unbiased way. We used known information on membership, when available, only for the few stars to be observed with UVES. Results. We collected spectra for 62 confirmed clusters in the main observing campaign (and a few more clusters were taken from the ESO archive). Among them are very young clusters, where the main targets are pre-main sequence stars, clusters with very hot and massive stars currently on the main sequence, intermediate-age and old clusters where evolved stars are the main targets. Our strategy of making the selection of targets as inclusive and unbiased as possible and of observing a significant and representative fraction of all possible targets permitted us to collect the largest, most accurate, and most homogeneous spectroscopic data set on open star clusters ever achieved.
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Tomšík, P., et M. Prokeš. « New strategic alliances of wine producers in the Czech Republic ; ». Agricultural Economics (Zemědělská ekonomika) 57, No. 12 (22 décembre 2011) : 573–79. http://dx.doi.org/10.17221/183/2011-agricecon.
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The paper describes the main reasons for the formation of new regional association of wineries, based on a different origin of wines in the wine region of Moravia in the southeast part of the Czech Republic. This research aim is to create a plan for a new development of such strategic alliances on the basis of results of the localization factors. The coefficient of localization is used for the identification of the cluster. The results are compared with the already operating associations for the appellation in Austria (DAC). There were traced changes in the consumer preferences in the Czech wine market. Consumers are placing more emphasis on the selection of wine on its descent from a particular area, the growing community and the individual grower. The dynamic development of the wine category, major changes in the market and the consumer demand are the main causes for the formation of associations of small and medium-sized wineries. This paper specifically introduces new associations for the appellation system VOC. This alliance is described in the context of the establishment, operation, development and expansion, respectively the possibility of the involvement of additional organizations suppliers and research institutions. The application of the results of research was a plan for the establishment of a new alliance VOC Modré Hory, where there are associated 30 wine producers of wine in 5 villages around the centre Velké Pavlovice. Based on the experience of the newly emerging VOC system of appellations, there was set up a plan of formation of the association with the proposed methodological approach. Open cooperation between the associations VOC appellation and other entities involving suppliers, customers, research institutions and universities has the possibility of creating an institutionalized wine cluster. The plan to create a wine cluster was proposed to establish the cooperation between the newly emerging associations of the VOC at three sub-regions of South Moravia, in order to achieve a competitive advantage.
25
Hojaev, Alisher S. « Galaxy open clusters and associations : study of stellar population ». Proceedings of the International Astronomical Union 2, S237 (août 2006) : 428. http://dx.doi.org/10.1017/s1743921307002165.
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Messina, S., D. Nardiello, S. Desidera, M. Baratella, S. Benatti, K. Biazzo et V. D’Orazi. « Gyrochronological dating of the stellar moving group Group X ». Astronomy & ; Astrophysics 657 (janvier 2022) : L3. http://dx.doi.org/10.1051/0004-6361/202142276.
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Context. Gyrochronology is one of the methods currently used to estimate the age of stellar open clusters. Hundreds of new clusters, associations, and moving groups unveiled by Gaia and complemented by accurate rotation period measurements provided by recent space missions such as Kepler and TESS are allowing us to significantly improve the reliability of this method. Aims. We use gyrochronology, that is, the calibrated age-mass-rotation relation valid for low-mass stars, to measure the age of the recently discovered moving group Group X. Methods. We extracted the light curves of all candidate members from the TESS full frame images and measured their rotation periods using different period search methods. Results. We measured the rotation period of 168 of a total of 218 stars and compared their period-colour distribution with those of two age-benchmark clusters, the Pleiades (125 Myr) and Praesepe (625 Myr), as well as with the recently characterised open cluster NGC 3532 (300 Myr). Conclusions. As result of our analysis, we derived a gyro age of 300 ± 60 Myr. We also applied as independent methods the fitting of the entire isochrone and of the three brightest candidate members individually with the most precise stellar parameters, deriving comparable values of 250 Myr and 290 Myr, respectively. Our dating of Group X allows us to definitively rule out the previously proposed connection with the nearby but much older Coma Berenices cluster.
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Hanke, Michael, Andreas Koch, Zdeněk Prudil, Eva K. Grebel et Ulrich Bastian. « Purveyors of fine halos ». Astronomy & ; Astrophysics 637 (mai 2020) : A98. http://dx.doi.org/10.1051/0004-6361/202037853.
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A long-lasting open question in the field of Galactic archeology refers to the size of the contribution from former globular cluster (GC) stars to the formation of the stellar halo of the Milky Way. We contribute to answering this important question by establishing observational links between the present-day halo field star population and GCs. To this end, we combined astrometric information such as space motions and parallaxes from the second data release of the Gaia mission (Gaia DR2) with spectroscopic radial velocities and metallicities ([Fe/H]) from the Sloan Digital Sky Survey (SDSS-IV, DR14) to end up with a seven-dimensional chemodynamical information space for more than 3 × 105 stars. Moreover, from our previous study, we incorporated the sample of halo giant stars with a distinct chemical signature (strong CN bandheads) that resembles the light-elements anomaly otherwise only seen in the second generation of globular cluster stellar populations. Using three different tagging techniques – among which is the exploration of conservative integrals of motion – we are able to establish unique associations between 151 extratidal stars in the neighborhood of eight GCs, which coincide with earlier findings of stellar envelopes beyond the tidal radius and even beyond (out to several tens of tidal radii). In addition, we trace the possible origin of about 62% of the sample of CN-strong giants to their potential host clusters. We find a connection between several of the involved GCs and the Gaia-Enceladus and Sequoia merger events. By establishing kinematic and chemical connections between 17 CN-strong stars and their surrounding fields, we identify co-moving groups of stars at the same [Fe/H] with a possible cluster origin. Some of these associations contain RR Lyrae variables, which allows meaningful distance inferences to be made. From these, we find strong evidence that four CN-strong stars and their associates are connected to the Sagittarius stream whilst their tightly confined [Fe/H] may hint to a birth site in M 54, the massive cluster in Sagittarius’ core remnant. Finally, by employing the counts of CN-strong and bona-fide CN-normal giants from our novel sample, we provide tentative estimates for the fraction of first-generation cluster stars among all stars lost to the halo. In the immediate cluster vicinity, this value amounts to 50.0 ± 16.7% while the associations in the halo field rather imply 80.2−5.2+4.9%. We speculate that – if proven real by spectroscopic follow-up – the disparity between these numbers could indicate a major contribution of low-mass clusters to the overall number of stars escaped to the halo or could alternatively suggest strong mass loss from the first generation during early cluster dissolution.
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Brown, Anthony. « OB Associations, Open Clusters, and the Luminosity Calibration of the Nearer Stars ». Highlights of Astronomy 12 (2002) : 665–68. http://dx.doi.org/10.1017/s1539299600014611.
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AbstractIn the context of the luminosity calibration of the nearer stars I discuss the Hipparcos results on distances to nearby OB associations and open clusters. The shortcomings and assumptions in the analyses used to derive these results are pointed out and for the open clusters a comparison is made with results obtained from main sequence fitting. I conclude that given the considerable uncertainties in the latter technique there is no convincing evidence that the Hipparcos based distances to open clusters beyond the Hyades should not be trusted.
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Hatzidimitriou, Despina, Charles J. Lada, Ata Sarajedini, Russell D. Cannon, Kyle McC Cudworth, Gary S. Da Costa, LiCai Deng, Young-Wook Lee, Ata Sarajedini et Monica Tosi. « COMMISSION 37 : STAR CLUSTERS AND ASSOCIATIONS ». Proceedings of the International Astronomical Union 4, T27A (décembre 2008) : 277–79. http://dx.doi.org/10.1017/s1743921308025684.
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Star clusters are valuable tools for theoretical and observational astronomy across a wide range of disciplines from cosmology to stellar spectroscopy. For example, properties of globular clusters are used to constrain stellar evolutionary models, nucleosynthesis and chemical evolution, as well as the star formation and assembly histories of galaxies and the distribution of dark matter in present-day galaxies. Open clusters are widely used as stellar laboratories for the study of specific stellar phenomena (e.g., various emission-line stars, pulsating pre-MS stars, magnetic massive stars, binarity, stellar rotation, etc.). They also provide observational constraints on models of massive star evolution and of Galactic disk formation and chemical evolution.
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Maslak, O., K. Doroshkevych et I. Salata. « Principles of formation and development of clustering systems of the national economy ». Scientific Messenger of LNU of Veterinary Medicine and Biotechnologies 20, no 86 (26 février 2018) : 68–72. http://dx.doi.org/10.15421/nvlvet8613.
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The article deals with the process of formation and development of clustering systems of the national economy, which ensures the generation of competitive advantages of enterprises, regions and the state as a whole and achievement of their competitiveness, ensuring rapid economic growth, achieving synergy effects, promoting the development of national trade and the formation of a favorable business environment, etc. At the same time, clusterization is considered in the article as a process of creating clusters and other network structures to achieve the goals of these associations by providing appropriate conditions and taking organizational and economic measures by their participants. Clusters are proposed to be considered as open systems, in which material, financial, labor and other resources, separate economic units, institutions, authorities are located at the entrance, and at the output – are products, profit, synergy effect, innovations, etc. The clusters consist of management and managed subsystems. Cluster management bodies may be formed from representatives of a managed subsystem, regional executive bodies or in a mixed form. The achievements of the mentioned advantages in the article are grounded from the point of observing the principles of clusterization as the basic laws, rules and regularities of the formation of cluster entities. The principles of clusterization in the article are summarized in the local (geographic localization, the tightness of economic ties, voluntary association of enterprises and organizations in clusters, systemic, resource support, public-private partnership, etc.), regional (priority of stimulating innovation activity, support of small and medium enterprises, systematic and interrelated with the strategic tasks of the development of related industries, unity and collegiality, etc.) and national (polycentrism, priority, the unity of the economic space, legality, etc.). This classification is aimed at forming a comprehensive understanding of clustering, gaining experience in its implementation, developing processes for the formation of clustering systems of the national economy.
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Fu, Tiwei, Xiangyu Fan, Quanxin Long, Wanyan Deng, Jinlin Song et Enyi Huang. « Comparative analysis of prophages in Streptococcus mutans genomes ». PeerJ 5 (17 novembre 2017) : e4057. http://dx.doi.org/10.7717/peerj.4057.
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Prophages have been considered genetic units that have an intimate association with novel phenotypic properties of bacterial hosts, such as pathogenicity and genomic variation. Little is known about the genetic information of prophages in the genome of Streptococcus mutans, a major pathogen of human dental caries. In this study, we identified 35 prophage-like elements in S. mutans genomes and performed a comparative genomic analysis. Comparative genomic and phylogenetic analyses of prophage sequences revealed that the prophages could be classified into three main large clusters: Cluster A, Cluster B, and Cluster C. The S. mutans prophages in each cluster were compared. The genomic sequences of phismuN66-1, phismuNLML9-1, and phismu24-1 all shared similarities with the previously reported S. mutans phages M102, M102AD, and ϕAPCM01. The genomes were organized into seven major gene clusters according to the putative functions of the predicted open reading frames: packaging and structural modules, integrase, host lysis modules, DNA replication/recombination modules, transcriptional regulatory modules, other protein modules, and hypothetical protein modules. Moreover, an integrase gene was only identified in phismuNLML9-1 prophages.
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Pigulski, A., G. Kopacki, Z. Kołaczkowski et M. Jerzykiewicz. « Pulsating B-Type Stars in Young Open Clusters ». International Astronomical Union Colloquium 185 (2002) : 146–47. http://dx.doi.org/10.1017/s0252921100015827.
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AbstractDuring the last several years about a dozen young northern clusters and associations have been observed in our program of searching for B-type variables. As far as B-type pulsators are concerned, we found that (i) young northern open clusters are a few times less abundant in β Cephei stars than the southern ones, (ii) all newly discovered SPB stars seem to be monoperiodic.
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Majaess, Daniel J., David G. Turner et David J. Lane. « In Search of Possible Associations between Planetary Nebulae and Open Clusters ». Publications of the Astronomical Society of the Pacific 119, no 862 (décembre 2007) : 1349–60. http://dx.doi.org/10.1086/524414.
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Gieren, Wolfgang P. « A note on several galactic Cepheids in open clusters and associations ». Publications of the Astronomical Society of the Pacific 100 (février 1988) : 262. http://dx.doi.org/10.1086/132164.
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Sterken, C., et M. Y. Bouzid. « Photometric Monitoring of Binaries in Open Clusters and Associations : NGC 6231 ». International Astronomical Union Colloquium 194 (juillet 2004) : 79–80. http://dx.doi.org/10.1017/s0252921100151991.
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AbstractOver the last couple of years we carried out long-term CCD monitoring of open clusters and associations with as principal goal the detection and study of pulsating stars. A by-product of this project is the serendipitous collection of multicolour photometry of most interesting compact binaries which show signs of activity, viz. variable periods and strongly variable light curves. This presentation illustrates the project, and concentrates on intriguing species of interacting binaries in NGC 6231.
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Knödlseder, J., M. Cerviño, J. M. Le Duigou, G. Meynet, D. Schaerer et P. von Ballmoos. « Gamma-ray line emission from OB associations and young open clusters ». Astronomy & ; Astrophysics 390, no 3 (août 2002) : 945–60. http://dx.doi.org/10.1051/0004-6361:20020799.
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Da Costa, G. S. « AM-3 : An Intermediate-Age Star Cluster in the Extreme Outskirts of the SMC ». Symposium - International Astronomical Union 190 (1999) : 446–47. http://dx.doi.org/10.1017/s0074180900118522.
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The faint star cluster AM-3 is one of three such objects discovered by Madore & Arp (1979). AM-1 has since been shown to be one of the most distant of the Galaxy's halo globular clusters, while AM-2 is now recognized as a distant, reddened Galactic open cluster. AM-3, however, has been largely ignored despite the fact that it lies only ~4.5 degrees from the center of the SMC making association with the SMC a possibility. This possibility was strengthened by the results of Irwin (1990) who showed that AM-3 lies (in projection) just within the outermost density contours of the SMC field population.
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Hetem, Annibal, et Jane Gregorio-Hetem. « Fractal statistics in young star clusters : structural parameters and dynamical evolution ». Monthly Notices of the Royal Astronomical Society 490, no 2 (23 octobre 2019) : 2521–41. http://dx.doi.org/10.1093/mnras/stz2698.
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ABSTRACT We used fractal statistics to quantify the degree of observed substructures in a sample of 50 embedded clusters and more evolved open clusters (< 100 Myr) found in different galactic regions. The observed fractal parameters were compared with N-body simulations from the literature, which reproduce star-forming regions under different initial conditions and geometries that are related to the cluster's dynamical evolution. Parallax and proper motion from Gaia-DR2 were used to accurately determine cluster membership by using the Bayesian model and cross-entropy technique. The statistical parameters $\mathcal {Q}$, $\overline{m}$ and $\overline{s}$ were used to compare observed cluster structure with simulations. A low level of substructures ($\mathcal {Q} \lt $ 0.8) is found for most of the sample that coincides with simulations of regions showing fractal dimension D ∼ 2–3. Few clusters (<20 per cent) have uniform distribution with a radial density profile (α < 2). A comparison of $\mathcal {Q}$ with mass segregation (ΛMSR) and local density as a function of mass (ΣLDR) shows the clusters coinciding with models that adopt supervirial initial conditions. The age–crossing time plot indicates that our objects are dynamically young, similar to the unbound associations found in the Milky Way. We conclude that this sample may be expanding very slowly. The flat distribution in the $\mathcal {Q}$–age plot and the absence of trends in the distributions of ΛMSR and ΣLDR against age show that in the first 10 Myr the clusters did not change structurally and seem not to have expanded from a much denser region.
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Santamar, Celina, Julio Gonzalo et Felisa Verdejo. « Automatic Association of Web Directories with Word Senses ». Computational Linguistics 29, no 3 (septembre 2003) : 485–502. http://dx.doi.org/10.1162/089120103322711613.
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We describe an algorithm that combines lexical information (from WordNet 1.7) with Web directories (from the Open Directory Project) to associate word senses with such directories. Such associations can be used as rich characterizations to acquire sense-tagged corpora automatically, cluster topically related senses, and detect sense specializations. The algorithm is evaluated for the 29 nouns (147 senses) used in the Senseval 2 competition, obtaining 148 (word sense, Web directory) associations covering 88% of the domain-specific word senses in the test data with 86% accuracy. The richness of Web directories as sense characterizations is evaluated in a supervised word sense disambiguation task using the Senseval 2 test suite. The results indicate that, when the directory/word sense association is correct, the samples automatically acquired from the Web directories are nearly as valid for training as the original Senseval 2 training instances. The results support our hypothesis that Web directories are a rich source of lexical information: cleaner, more reliable, and more structured than the full Web as a corpus.
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Topasna, G. A., N. T. Kaltcheva et E. Paunzen. « Interstellar polarization and extinction towards the young open cluster NGC 1502 ». Astronomy & ; Astrophysics 615 (juillet 2018) : A166. http://dx.doi.org/10.1051/0004-6361/201731903.
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Aims. NGC 1502 is located at the periphery of the Cam OB1 association and probably within the Orion Spur, with published distance estimates varying between 0.7 and 1.5 kpc. We combine new polarimetric observations and existing uvbyβ and UBV photometries to provide new estimates of the cluster’s parameters. Methods. We present new multi-wavelength polarization observations of 22 stars in the direction of the cluster and, using the wavelength of maximum polarization, calculate the total-to-selective extinction ratio for each of these stars. These are combined with homogenized uvbyβ and UBV photometries to obtain the individual stellar distances and study the structure of the field. Results. We found no evidence of significant extinction variation across the cluster and obtained an average color excess E(b − y) = 0.56 ± 0.02 mag, corresponding to E(B − V) = 0.76 mag. Given the uniformity of both pmax and λmax toward the cluster and the distribution of the color excess with distance, it seems likely that the polarization in this region arises from aligned dust grains in the foreground of the cluster, not farther than 500–600 pc. Based on 20 stars located beyond 500 pc within the studied field of view, we obtained an average polarization-based total-to-selective extinction ratio R = 2.83 ± 0.14 yielding visual absorption AV = 2.14 ± 0.16 mag. Using 11 stars with uvbyβ data that represent the main sequence of the cluster, we calculated a photometric distance of 1117−89+96 pc. This estimate is fully supported by the UBV -based analysis and the new individual membership probabilities that we derive. Assuming a solar metallicity yields an age of 5 Myr. Our analysis yields controversial results regarding the membership of the stars associated with the SZ Cam system (HD 25638 and HD 25639) to the cluster.
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Criss, Robert E., et Anne M. Hofmeister. « Quantification of Sub-Solar Star Ages from the Symmetry of Conjugate Histograms of Spin Period and Angular Velocity ». Symmetry 13, no 8 (18 août 2021) : 1519. http://dx.doi.org/10.3390/sym13081519.
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Empirical laws proposed for the decline in star spin with time have heretofore been tested using ambiguous fitting models. We develop an analytical inverse model that uses histogram data to unequivocally determine the physical law governing how dwarf star spin depends on time (t) and mass (M). We analyze shapes of paired histograms of axial rotation period (П) and angular velocity (ω = 2π/П) to utilize the fact that a variable and its reciprocal are governed by the same physics. Copious data on open clusters are used to test the formula ∂ω/∂t ∝ − ωn where n is unrestricted, and thus covers diverse possibilities. Histogram conjugates for each of 15 clusters with 120 to 812 measurements provide n = 1.13 ± 0.19. Results are independent of initial spin rate, bin size, cluster parameters, and star mass. Notably, 11 large clusters with mostly M-types yield fits with n = 1.07 ± 0.12. Associations behave similarly. Only exponential decay (n = 1) explains the similar shapes of the conjugate histograms for the spin period and angular velocity, despite the asymmetric (inverse) relationship of these variables. This rate law is consistent with viscous dissipation. Forward modeling confirms that n is near unity and further shows that coeval formation of all stars in a cluster does not occur. We therefore explore a constant rate of star production, which is reasonable for tiny stars. Inverse models show that episodic production increases with mass, but is unimportant below ~0.55 MSun. We infer star and cluster ages, and find that star production becomes less regular with time, as interstellar gas and dust are progressively depleted. Our new analytical approach of extracting a physical law from conjugate histograms is general and widely applicable.
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Hall, Michael W., Robin R. Rohwer, Jonathan Perrie, Katherine D. McMahon et Robert G. Beiko. « Ananke : temporal clustering reveals ecological dynamics of microbial communities ». PeerJ 5 (26 septembre 2017) : e3812. http://dx.doi.org/10.7717/peerj.3812.
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Taxonomic markers such as the 16S ribosomal RNA gene are widely used in microbial community analysis. A common first step in marker-gene analysis is grouping genes into clusters to reduce data sets to a more manageable size and potentially mitigate the effects of sequencing error. Instead of clustering based on sequence identity, marker-gene data sets collected over time can be clustered based on temporal correlation to reveal ecologically meaningful associations. We present Ananke, a free and open-source algorithm and software package that complements existing sequence-identity-based clustering approaches by clustering marker-gene data based on time-series profiles and provides interactive visualization of clusters, including highlighting of internal OTU inconsistencies. Ananke is able to cluster distinct temporal patterns from simulations of multiple ecological patterns, such as periodic seasonal dynamics and organism appearances/disappearances. We apply our algorithm to two longitudinal marker gene data sets: faecal communities from the human gut of an individual sampled over one year, and communities from a freshwater lake sampled over eleven years. Within the gut, the segregation of the bacterial community around a food-poisoning event was immediately clear. In the freshwater lake, we found that high sequence identity between marker genes does not guarantee similar temporal dynamics, and Ananke time-series clusters revealed patterns obscured by clustering based on sequence identity or taxonomy. Ananke is free and open-source software available at https://github.com/beiko-lab/ananke.
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Gieren, Wolfgang P., et Pascal Fouqué. « Comparison of the Galactic Cepheid Open Cluster and Surface Brightness Distance Scales ». International Astronomical Union Colloquium 155 (1995) : 365–66. http://dx.doi.org/10.1017/s0252921100037520.
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AbstractWe compare the best determined Baade-Wesselink (BW) period-luminosity (PL) relation for 100 galactic Cepheids to the PL relation derived for 32 open cluster and association Cepheids by the ZAMS-fitting method. Eighteen stars in common lead to the conclusion that BW and ZAMS-fitting distances can agree to better than 0.1 mag, after proper allowance of systematic effects in both methods.
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Caballero, J. A., A. de Burgos, F. J. Alonso-Floriano, A. Cabrera-Lavers, D. García-Álvarez et D. Montes. « Stars and brown dwarfs in the σ Orionis cluster ». Astronomy & ; Astrophysics 629 (septembre 2019) : A114. http://dx.doi.org/10.1051/0004-6361/201935987.
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Context. Only a few open clusters are as important for the study of stellar and substellar objects, and their formation and evolution, as the young σ Orionis cluster. However, a complete spectroscopic characterisation of its whole stellar population is still missing. Aims. We filled most of that gap with a large spectroscopic and astrometric survey of targets towards σ Orionis. Eventually, it will be one of the open clusters with the lowest proportion of interlopers and the largest proportion of confirmed cluster members with known uncontrovertible youth features. Methods. We acquired 317 low-resolution optical spectra with the Intermediate Dispersion Spectrograph (IDS) at the 2.5 m Isaac Newton Telescope (INT) and the Optical System for Imaging and low Resolution Integrated Spectroscopy (OSIRIS) at the 10.4 m Gran Telescopio Canarias (GTC). We measured equivalent widths of Li I, Hα, and other key lines from these spectra, and determined spectral types. We complemented this information with Gaia DR2 astrometric data and other features of youth (mid-infrared excess, X-ray emission) compiled with Virtual Observatory tools and from the literature. Results. Of the 168 observed targets, we determined for the first time spectral types of 39 stars and equivalent widths of Li I and Hα of 34 and 12 stars, respectively. We identified 11 close (ρ ≲ 3 arcsec) binaries resolved by Gaia, of which three are new, 14 strong accretors, of which four are new and another four have Hα emission shifted by over 120 km s−1, two juvenile star candidates in the sparse population of the Ori OB1b association, and one spectroscopic binary candidate. Remarkably, we found 51 non-cluster-members, 35 of which were previously considered as σ Orionis members and taken into account in high-impact works on, for example, disc frequency and initial mass function.
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VERDÚ, M. E., P. COLL, J. A. VÁZQUEZ, F. MARCH, D. FONTANALS, S. BERRÓN, I. PONS, D. VAN ESSO et G. PRATS. « Association between asymptomatic carriage and sporadic (endemic) meningococcal disease in an open community ». Epidemiology and Infection 127, no 2 (octobre 2001) : 245–59. http://dx.doi.org/10.1017/s095026880100591x.
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We analysed a strain collection representative of the overall Neisseria meningitidis population circulating in an open community (46000 inhabitants, Spain) during an endemic period (30 isolates from patients and 191 from throat cultures of healthy individuals) by both phenotypic and molecular techniques. Almost all patient isolates were assigned to three hyper-virulent lineages (ET-5 complex, ET-37 complex and cluster A4) by both multilocus enzyme electrophoresis (MEE) and pulsed-field gel electrophoresis (PFGE). In contrast, MEE and PFGE assigned 20% and 15% respectively of carrier isolates to the hyper-virulent clones (4% for both methods together). There was also a higher correlation between PFGE and phenotypes associated with virulent clones. These notable differences between the two molecular methods were further observed in more than half the carrier isolates, suggesting that the associations between these strains were distorted by recombination events. However, almost one-third of total endemic strains from symptom-free carriers and almost all patient strains belonged to clones defined by MEE and PFGE, with no known epidemiological connection. These data indicate low transmission and a weak clonal structure for N. meningitidis.
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Lin, Chien-Cheng, W. P. Chen et Neelam Panwar. « CHARACTERIZATION OF THE YOUNG OPEN CLUSTER G144.9+0.4 IN THE CAMELOPARDALIS OB1 ASSOCIATION ». Astrophysical Journal 775, no 2 (13 septembre 2013) : 123. http://dx.doi.org/10.1088/0004-637x/775/2/123.
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Gutiérrez Albarrán, M. L., D. Montes, M. Gómez Garrido, H. M. Tabernero, J. I. González Hernández, E. Marfil, A. Frasca et al. « The Gaia-ESO Survey : Calibrating the lithium–age relation with open clusters and associations ». Astronomy & ; Astrophysics 643 (novembre 2020) : A71. http://dx.doi.org/10.1051/0004-6361/202037620.
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Context. Previous studies of open clusters have shown that lithium depletion is not only strongly age dependent but also shows a complex pattern with other parameters that is not yet understood. For pre- and main-sequence late-type stars, these parameters include metallicity, mixing mechanisms, convection structure, rotation, and magnetic activity. Aims. We perform a thorough membership analysis for a large number of stars observed within the Gaia-ESO survey (GES) in the field of 20 open clusters, ranging in age from young clusters and associations, to intermediate-age and old open clusters. Methods. Based on the parameters derived from the GES spectroscopic observations, we obtained lists of candidate members for each of the clusters in the sample by deriving radial velocity distributions and studying the position of the kinematic selections in the EW(Li)-versus-Teff plane to obtain lithium members. We used gravity indicators to discard field contaminants and studied [Fe/H] metallicity to further confirm the membership of the candidates. We also made use of studies using recent data from the Gaia DR1 and DR2 releases to assess our member selections. Results. We identified likely member candidates for the sample of 20 clusters observed in GES (iDR4) with UVES and GIRAFFE, and conducted a comparative study that allowed us to characterize the properties of these members as well as identify field contaminant stars, both lithium-rich giants and non-giant outliers. Conclusions. This work is the first step towards the calibration of the lithium–age relation and its dependence on other GES parameters. During this project we aim to use this relation to infer the ages of GES field stars, and identify their potential membership to young associations and stellar kinematic groups of different ages.
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Kaltcheva, N. T., et L. N. Georgiev. « Stromgren and H photometry of OB associations and open clusters - I. ARA OB1 ». Monthly Notices of the Royal Astronomical Society 259, no 1 (1 novembre 1992) : 166–74. http://dx.doi.org/10.1093/mnras/259.1.166.
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Bobylev, V. V., et A. T. Bajkova. « Gould Belt kinematics on the basis of the open clusters and OB associations ». Astronomical & ; Astrophysical Transactions 25, no 2-3 (avril 2006) : 139–42. http://dx.doi.org/10.1080/10556790600893088.
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Ivanov, Anton A., Pavel A. Abramov, Mohamed Haouas, Yann Molard, Stéphane Cordier, Clément Falaise, Emmanuel Cadot et Michael A. Shestopalov. « Supramolecular Host–Guest Assemblies of [M6Cl14]2–, M = Mo, W, Clusters with γ-Cyclodextrin for the Development of CLUSPOMs ». Inorganics 11, no 2 (7 février 2023) : 77. http://dx.doi.org/10.3390/inorganics11020077.
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Host–guest assemblies open up opportunities for developing novel functional CLUSPOM multicomponent systems based on transition metal clusters (CLUS), polyoxometalates (POMs) and macrocyclic organic ligands. In water–ethanol solution γ-cyclodextrin (γ-CD) interacts with halide metal clusters [M6Cl14]2– (M = Mo, W) to form sandwich-type structures. The supramolecular association between the clusters and CDs, however, remains weak in solution, and the interactions are not strong enough to prevent the hydrolysis of the inorganic guest. Although analysis of the resulting crystal structures reveals inclusion complexation, 1H NMR experiments in solution show no specific affinity between the two components. The luminescent properties of the host–guest compounds in comparison with the initial cluster complexes are also studied to evaluate the influence of CD.