Articles de revues sur le sujet « Young cluster »
Pour voir les autres types de publications sur ce sujet consultez le lien suivant : Young cluster.
Créez une référence correcte selon les styles APA, MLA, Chicago, Harvard et plusieurs autres
Consultez les 50 meilleurs articles de revues pour votre recherche sur le sujet « Young cluster ».
À côté de chaque source dans la liste de références il y a un bouton « Ajouter à la bibliographie ». Cliquez sur ce bouton, et nous générerons automatiquement la référence bibliographique pour la source choisie selon votre style de citation préféré : APA, MLA, Harvard, Vancouver, Chicago, etc.
Vous pouvez aussi télécharger le texte intégral de la publication scolaire au format pdf et consulter son résumé en ligne lorsque ces informations sont inclues dans les métadonnées.
Parcourez les articles de revues sur diverses disciplines et organisez correctement votre bibliographie.
1
Randriamanakoto, Zara, et Petri Väisänen. « Young massive clusters in Arp 299 ». Proceedings of the International Astronomical Union 14, S351 (mai 2019) : 143–46. http://dx.doi.org/10.1017/s1743921319007701.
Texte intégralRésumé :
AbstractBecause of their young ages and compact densities, young massive star clusters (YMCs) are widely considered as potential proto-globular clusters. They are ubiquitous in environments with ongoing star formation activity such as interacting luminous infrared galaxies. To determine the galactic environmental effects on the star cluster formation and evolution, we study the YMC population of Arp 299 (NGC 3690E/NGC 3690W) using data taken with the HST WFC3/UVIS camera. By fitting the multiband photometry with the Yggdrasil models, we derive the star cluster masses, ages and extinction. While the cluster mass-galactocentric radius relation of NGC 3690E indicates that there could be an influence of the gas density distribution on the cluster formation, the age distribution of the western component suggests that YMCs in that galaxy endure stronger disruption mechanisms. With a cluster formation efficiency of 19 percent, star formation happening in bound clusters in Arp 299 is 3–5 times higher than that of a typical normal spiral.
2
Brown, Gillen, et Oleg Y. Gnedin. « Radii of young star clusters in nearby galaxies ». Monthly Notices of the Royal Astronomical Society 508, no 4 (8 octobre 2021) : 5935–53. http://dx.doi.org/10.1093/mnras/stab2907.
Texte intégralRésumé :
ABSTRACT We measure the projected half-light radii of young star clusters in 31 galaxies from the Legacy Extragalactic UV Survey (LEGUS). We implement a custom pipeline specifically designed to be robust against contamination, which allows us to measure radii for 6097 clusters. This is the largest sample of young star cluster radii currently available. We find that most (but not all) galaxies share a common cluster radius distribution, with the peak at around 3 pc. We find a clear mass–radius relation of the form Reff ∝ M0.24. This relation is present at all cluster ages younger than 1 Gyr, but with a shallower slope for clusters younger than 10 Myr. We present simple toy models to interpret these age trends, finding that high-mass clusters are more likely to be not tidally limited and expand. We also find that most clusters in LEGUS are gravitationally bound, especially at older ages or higher masses. Lastly, we present the cluster density and surface density distributions, finding a large scatter that appears to decrease with cluster age. The youngest clusters have a typical surface density of 100$\, \mathrm{ M}_\odot \, \mathrm{pc}^{-2}$.
3
Rosenberg, A., I. Saviane, G. Piotto, S. Zaggia et A. Aparicio. « Pal 1 : Another Young Globular Cluster ? » Symposium - International Astronomical Union 174 (1996) : 341–42. http://dx.doi.org/10.1017/s0074180900001728.
Texte intégralRésumé :
We present a color magnitude diagram (CMD) in the V and I bands reaching ∼ 4 magnitudes below the turn off (TO) for the galactic globular (?) cluster Pal 1. A comparison with other well-observed clusters and theoretical models suggests that Pal 1 has an age of 8±2 Gyrs, which would make it the youngest globular cluster of our Galaxy.
4
Cox, Georgina R., Jo Robinson, Michelle Williamson, Anne Lockley, Yee Tak Derek Cheung et Jane Pirkis. « Suicide Clusters in Young People ». Crisis 33, no 4 (1 juillet 2012) : 208–14. http://dx.doi.org/10.1027/0227-5910/a000144.
Texte intégralRésumé :
Background: Suicide clusters have commonly been documented in adolescents and young people. Aims: The current review conducts a literature search in order to identify and evaluate postvention strategies that have been employed in response to suicide clusters in young people. Methods: Online databases, gray literature, and Google were searched for relevant articles relating to postvention interventions following a suicide cluster in young people. Results: Few studies have formally documented response strategies to a suicide cluster in young people, and at present only one has been longitudinally evaluated. However, a number of strategies show promise, including: developing a community response plan; educational/psychological debriefings; providing both individual and group counseling to affected peers; screening high risk individuals; responsible media reporting of suicide clusters; and promotion of health recovery within the community to prevent further suicides. Conclusions: There is a gap in formal evidence-based guidelines detailing appropriate postvention response strategies to suicide clusters in young people. The low-frequency nature of suicide clusters means that long-term systematic evaluation of response strategies is problematic. However, some broader suicide prevention strategies could help to inform future suicide cluster postvention responses.
5
Anders, Peter, Uta Fritze –. v. Alvensleben et Richard de Grijs. « Young Star Clusters : Progenitors of Globular Clusters! ? » Highlights of Astronomy 13 (2005) : 366–68. http://dx.doi.org/10.1017/s1539299600015987.
Texte intégralRésumé :
AbstractStar cluster formation is a major mode of star formation in the extreme conditions of interacting galaxies and violent starbursts. Young clusters are observed to form in a variety of such galaxies, a substantial number resembling the progenitors of globular clusters in mass and size, but with significantly enhanced metallicity. From studies of the metal-poor and metal-rich star cluster populations of galaxies, we can therefore learn about the violent star formation history of these galaxies, and eventually about galaxy formation and evolution. We present a new set of evolutionary synthesis models of our GALEV code, with special emphasis on the gaseous emission of presently forming star clusters, and a new tool to compare extensive model grids with multi-color broad-band observations to determine individual cluster masses, metallicities, ages and extinction values independently. First results for young star clusters in the dwarf starburst galaxy NGC 1569 are presented. The mass distributions determined for the young clusters give valuable input to dynamical star cluster system evolution models, regarding survival and destruction of clusters. We plan to investigate an age sequence of galaxy mergers to see dynamical destruction effects in process.
6
Webb, Jeremy J., et Alison Sills. « The initial properties of young star clusters in M83 ». Monthly Notices of the Royal Astronomical Society 501, no 2 (12 décembre 2020) : 1933–39. http://dx.doi.org/10.1093/mnras/staa3832.
Texte intégralRésumé :
ABSTRACT The initial sizes and masses of massive star clusters provide information about the cluster formation process and also determine how cluster populations are modified and destroyed, which have implications for using clusters as tracers of galaxy assembly. Young massive cluster populations are often assumed to be unchanged since cluster formation; therefore, their distributions of masses and radii are used as the initial values. However, the first few hundred million years of cluster evolution does change both cluster mass and cluster radius, through both internal and external processes. In this paper, we use a large suite of N-body cluster simulations in an appropriate tidal field to determine the best initial mass and initial size distributions of young clusters in the nearby galaxy M83. We find that the initial masses follow a power-law distribution with a slope of −2.7 ± 0.4 , and the half-mass radii follow a lognormal distribution with a mean of 2.57 ± 0.04 pc and a dispersion of 1.59 ± 0.01 pc. The corresponding initial projected half-light radius function has a mean of 2.7 ± 0.3 pc and a dispersion of 1.7 ± 0.2 pc. The evolution of the initial mass and size distribution functions is consistent with mass-loss and expansion due to stellar evolution, independent of the external tidal field and the cluster’s initial density profile. Observed cluster sizes and masses should not be used as the initial values, even when clusters are only a few hundred million years old.
7
Grosbøl, P., et H. Dottori. « Expulsion of Dust from Young Stellar Clusters ». Proceedings of the International Astronomical Union 8, S292 (août 2012) : 287. http://dx.doi.org/10.1017/s1743921313001415.
Texte intégralRésumé :
AbstractYoung stellar clusters were identified on deep near-infrared images of 6 nearby, grand-design spirals observed with HAWK-I/VLT. A 90% completeness was reached for cluster complexes with MK = −11.5m (corresponding to masses around 104 M⊙) while the linear resolution was around 40 pc. The distribution of clusters in the (H-K)–(J-H) diagrams revealed two groups of clusters. Comparing with Starburst99 model tracks, the groups could be interpreted as one old population of clusters with low extinction and one consisting of young clusters with visual extinction as high as AV = 7m. The clear separation between the two groups suggests a rapid expulsion of dust from the young clusters.Monte-Carlo models were made assuming a cluster distribution function g(Mc, τ) = Mc−a τ−γ where Mc and τ are cluster mass and age, respectively. Fitting such models to the observed NIR color distributions, it was concluded that the cluster mortality had to be significant with γ = 0.8-1.0. Further, the star formation phase of clusters has to extend over several Myr. Young clusters have high extinctions at least the first 3 Myr but then lose their reddening over a period of around 5 Myr, depending on the exact evolutionary tracks used.
8
Rochau, Boyke, Wolfgang Brandner, Andrea Stolte, Mario Gennaro et Thomas Henning. « Internal dynamics of the NGC 3603 young cluster ». Proceedings of the International Astronomical Union 5, S266 (août 2009) : 517. http://dx.doi.org/10.1017/s174392130999189x.
Texte intégralRésumé :
AbstractStarburst clusters are spectacular young and dense stellar systems containing copious numbers of massive O-type and Wolf–Rayet stars. These objects depict a stellar population comprising stars over the entire mass range, making them ideal objects to study cluster formation and evolution as well as to test and calibrate stellar evolutionary models. Among the Galactic spiral-arm starburst clusters, NGC 3603 Young Cluster (YC), which is located in the Carina spiral arm, is the youngest and most compact one. Galactic starburst clusters also serve as templates for extragalactic super star clusters as observed, e.g., in the Antennae galaxies. Based on two epochs (obtained 10 yr apart) of high-quality astrometric HST/WFPC2 observations, we derive individual proper motions for several hundred stars. The proper motions enable us to distinguish cluster members from field stars, and to derive a first estimate of the internal cluster dynamics. Photometry of the clean sample of cluster stars allows us to create color–magnitude diagrams (CMDs) that are not contaminated by field stars, and to compare the sequence of cluster members with different sets of theoretical isochrones and evolutionary tracks. We clearly identify a lower-mass pre-main-sequence and a higher-mass main-sequence stellar population in NGC 3603. A particular focus of our comparison with theoretical isochrones is the exact shape and extent of the pre-main-sequence/main-sequence transition region in NGC 3603 YC. The proper motions also contain dynamical information. From this, we derive a velocity dispersion, which leads to the first dynamical mass estimate of the NGC 3603 cluster. We also investigate whether or not NGC 3603 YC is virialized, and study evidence for primordial versus dynamical mass segregation. Past and future evolution of NGC 3603 YC can be studied and will tell us about the clusters ‘fate’ and its long-term survival chances.
9
Larsen, Søren S. « Open, Massive and Globular Clusters — Part of the Same Family ? » Symposium - International Astronomical Union 207 (2002) : 421–27. http://dx.doi.org/10.1017/s0074180900224133.
Texte intégralRésumé :
Populations of young star clusters show significant differences even among “normal” disk galaxies. In this contribution I discuss how properties of young cluster systems are related to those of their host galaxies, based on a recent study of clusters in a sample of 22 nearby spiral galaxies. Luminous young clusters similar to the “super” star clusters observed in starbursts and mergers exist in several of these galaxies, and it is found that the luminosity of the brightest star cluster as well as the specific luminosity of the cluster systems both correlate well with the host galaxy star formation rate. When considering star clusters in different environments the traditional distinction between “open”, “massive” and “globular” clusters breaks down, underscoring the need for a universal physical description of cluster formation.
10
Hashimoto, Tetsuya, Tomotsugu Goto, Rieko Momose, Chien-Chang Ho, Ryu Makiya, Chia-Ying Chiang et Seong Jin Kim. « A young galaxy cluster in the old Universe ». Monthly Notices of the Royal Astronomical Society 489, no 2 (12 août 2019) : 2014–29. http://dx.doi.org/10.1093/mnras/stz2182.
Texte intégralRésumé :
ABSTRACT Galaxies evolve from a blue star-forming phase into a red quiescent one by quenching their star formation activity. In high-density environments, this galaxy evolution proceeds earlier and more efficiently. Therefore, local galaxy clusters are dominated by well-evolved red elliptical galaxies. The fraction of blue galaxies in clusters monotonically declines with decreasing redshift, i.e. the Butcher–Oemler effect. In the local Universe, observed blue fractions of massive clusters are as small as ≲0.2. Here we report a discovery of a ‘blue cluster’ that is a local galaxy cluster with an unprecedentedly high fraction of blue star-forming galaxies yet hosted by a massive dark matter halo. The blue fraction is 0.57, which is 4.0σ higher than those of the other comparison clusters under the same selection and identification criteria. The velocity dispersion of the member galaxies is 510 km s−1, which corresponds to a dark matter halo mass of 2.0$^{+1.9}_{-1.0}\times 10^{14}$ M⊙. The blue fraction of the cluster is more than 4.7σ beyond the standard theoretical predictions including semi-analytic models of galaxy formation. The probability to find such a high blue fraction in an individual cluster is only 0.003 per cent, which challenges the current standard frameworks of the galaxy formation and evolution in the ΛCDM universe. The spatial distribution of galaxies around the blue cluster suggests that filamentary cold gas streams can exist in massive haloes even in the local Universe. However these cold streams have already disappeared in the theoretically simulated local universes.
11
Goodwin, Simon P. « The theory of young cluster disruption ». Proceedings of the International Astronomical Union 6, S270 (mai 2010) : 283–86. http://dx.doi.org/10.1017/s1743921311000512.
Texte intégralRésumé :
AbstractMost stars seem to form in clusters, but the vast majority of these clusters do not seem to survive much beyond their embedded phase. The most favoured mechanism for the early destruction of star clusters is the effect of the removal of residual gas by feedback which dramatically changes the cluster potential. The effects of feedback depend on the ratio of the masses of stars and gas, and the velocity dispersion of the stars at the onset of gas removal. As gas removal is delayed by a few Myr from star formation these crucial parameters can change significantly from their initial values. In particular, in dynamically cool and clumpy clusters, the stars will collapse to a far denser state and if they decouple from the gas then gas removal may be far less destructive than previously thought. This might well help explain the survival of very massive clusters, such as globular clusters, without the need for extremely high star formation efficiencies or initial masses far greater than their current masses.
12
Pfeffer, Joel, Nate Bastian, J. M. Diederik Kruijssen, Marta Reina-Campos, Robert A. Crain et Christopher Usher. « Young star cluster populations in the E-MOSAICS simulations ». Monthly Notices of the Royal Astronomical Society 490, no 2 (3 octobre 2019) : 1714–33. http://dx.doi.org/10.1093/mnras/stz2721.
Texte intégralRésumé :
ABSTRACT We present an analysis of young star clusters (YSCs) that form in the E-MOSAICS cosmological, hydrodynamical simulations of galaxies and their star cluster populations. Through comparisons with observed YSC populations, this work aims to test models for YSC formation and obtain an insight into the formation processes at work in part of the local galaxy population. We find that the models used in E-MOSAICS for the cluster formation efficiency and high-mass truncation of the initial cluster mass function ($M_\rm {c,\ast }$) both quantitatively reproduce the observed values of cluster populations in nearby galaxies. At higher redshifts (z ≥ 2, near the peak of globular cluster formation) we find that, at a constant star formation rate (SFR) surface density, $M_\rm {c,\ast }$ is larger than at z = 0 by a factor of four due to the higher gas fractions in the simulated high-redshift galaxies. Similar processes should be at work in local galaxies, offering a new way to test the models. We find that cluster age distributions may be sensitive to variations in the cluster formation rate (but not SFR) with time, which may significantly affect their use in tests of cluster mass-loss. By comparing simulations with different implementations of cluster formation physics, we find that (even partially) environmentally independent cluster formation is inconsistent with the brightest cluster-SFR and specific luminosity-$\Sigma _\rm {SFR}$ relations, whereas these observables are reproduced by the fiducial, environmentally varying model. This shows that models in which a constant fraction of stars form in clusters are inconsistent with observations.
13
Mermilliod, Jean-Claude, et Beatriz García. « Spectroscopic Binaries in Young Open Clusters ». Symposium - International Astronomical Union 200 (2001) : 191–98. http://dx.doi.org/10.1017/s0074180900225217.
Texte intégralRésumé :
We have analysed the binarity and multiplicity characteristics of 120 O-type stars in 22 very young open clusters and found marked differences between the “rich” (N ≥ 6 O-type stars and primaries) and “poor” (N = 1) clusters. In the rich clusters, the binary frequencies vary between 14% (1 SB among 7 stars) and 80% (8 SBs among 10 stars). Multiple systems seem not to be frequent and stars are spread all over the cluster area. In poor clusters, the binary frequency of the O-type objects is nearly 100%, with orbital periods around 3 days. Several binaries are also eclipsing. Additional companions are always present. They form either hierarchical multiple stars or trapezium systems. These massive multiple systems are generally found close to the cluster center, although there are exceptions.
14
Larsen, Søren S. « HST Observations of Young Stellar Clusters in Nearby Galaxies ». Highlights of Astronomy 13 (2005) : 183–84. http://dx.doi.org/10.1017/s1539299600015550.
Texte intégralRésumé :
AbstractThe HST data archive contains images of several nearby spirals, suitable for detailed studies of the properties of individual star clusters and their surroundings. By combining structural information derived from HST images with ground-based photometry, it is possible to study cluster properties as a function of age and mass. While both the core and effective radii of young clusters correlate with mass, the slopes of these relations are shallower than for a constant-density relation, implying that the mean density increases with cluster mass. This must be accounted for in theories for cluster formation.
15
Buckner, Anne S. M., Zeinab Khorrami, Marta González, Stuart L. Lumsden, Paul Clark et Estelle Moraux. « The spatial evolution of young massive clusters ». Astronomy & ; Astrophysics 659 (mars 2022) : A72. http://dx.doi.org/10.1051/0004-6361/202140902.
Texte intégralRésumé :
Context. With the third release of the high-precision optical-wavelength Gaia survey, we are in a better position than ever before to study young clusters. However, Gaia is limited in the optical down to G ∼ 21 mag, and therefore it is essential to understand the biases introduced by a magnitude-limited sample on spatial distribution studies. Aims. We ascertain how sample incompleteness in Gaia observations of young clusters affects the local spatial analysis tool INDICATE and subsequently the perceived spatial properties of these clusters. Methods. We created a mock Gaia cluster catalogue from a synthetic dataset using the observation generating tool MYOSOTIS. The effect of cluster distance, uniform and variable extinction, binary fraction, population masking by the point spread function wings of high-mass members, and contrast sensitivity limits on the trends identified by INDICATE are explored. A comparison of the typical index values derived by INDICATE for members of the synthetic dataset and their corresponding mock Gaia catalogue observations is made to identify any significant changes. Results. We typically find only small variations in the pre- and post-observation index values of cluster populations, which can increase as a function of incompleteness percentage and binarity. No significant strengthening or false signatures of stellar concentrations are found, but real signatures may be diluted. Conclusions drawn about the spatial behaviour of Gaia-observed cluster populations that are, and are not, associated with their natal nebulosity are reliable for most clusters, but the perceived behaviours of individual members can change, so INDICATE should be used as a measure of spatial behaviours between members as a function of their intrinsic properties (e.g., mass, age, object type), rather than to draw conclusions about any specific observed member. Conclusions. INDICATE is a robust spatial analysis tool to reliably study Gaia-observed young cluster populations within 1 kpc, up to a sample incompleteness of 83.3% and binarity of 50%.
16
Martins, F., A. N. Chené, J. C. Bouret, J. Borissova, J. Groh, S. Ramírez Alegría et D. Minniti. « Massive stars in the young cluster VVV CL074 ». Astronomy & ; Astrophysics 627 (juillet 2019) : A170. http://dx.doi.org/10.1051/0004-6361/201935605.
Texte intégralRésumé :
Context. The evolution of massive stars is not fully constrained. Studies of young massive clusters hosting various populations of massive stars can help refine our understanding of the life and fate of massive stars. Aims. In this context, our goal is to study the massive stellar content of the young massive cluster VVV CL074. Methods. We obtained K-band spectroscopy of the brightest cluster members in order to identify the massive star population. We also determined the stellar properties of the cluster’s massive stars to better quantify the evolutionary sequences linking different types of massive stars. We collected integral field spectroscopy of selected fields in the cluster VVV CL074 with SINFONI on the ESO/VLT. We performed a spectral classification based on the K-band spectra and comparison to infrared spectral atlases. We determined the stellar parameters of the massive stars from analysis with atmosphere models computed with the code CMFGEN. Results. We uncover a population of 25 early-type (OB and Wolf–Rayet) stars, 19 being newly discovered by our observations out of which 15 are likely cluster members. The cluster’s spectrophotometric distance is 10.2 ± 1.6 kpc, placing it close to the intersection of the galactic bar and the Norma arm, beyond the galactic center. This makes VVV CL074 one the farthest young massive clusters identified so far. Among the massive stars population, three objects are Wolf–Rayet stars, the remaining are O and B stars. From the Hertzsprung–Russell diagram we find that most stars have an age between 3 and 6 Myr according to the Geneva evolutionary tracks. WN8 and WC8-9 stars are the descendants of stars with initial masses between 40 and 60 M⊙. The massive star population of VVV CL074 is very similar to that of the cluster DBS2003-179 and to a lesser extent to that of the Quintuplet cluster, indicating the same age. The central cluster of the Galaxy is ∼3 Myr older. From the comparison of the massive stars populations in these four clusters, one concludes that galactic stars with an initial mass in the range 40–60 M⊙ likely go through a WN8-9 phase.
17
Grebel, Eva K., Dennis Zaritsky, Jason Harris et Ian Thompson. « Young Magellanic Cloud Clusters (< ; 1 Gyr) : Census, Properties, Star Formation History ». Symposium - International Astronomical Union 190 (1999) : 405–9. http://dx.doi.org/10.1017/s0074180900118418.
Texte intégralRésumé :
We report preliminary results from an automated cluster survey of the Magellanic Clouds aimed at improving the cluster census and at deriving cluster properties from their resolved stellar content. The survey is tripling the number of known clusters. The cluster age distribution shows similar peaks at 100–200 Myr in LMC and SMC, coincident with the closest encounter of the Clouds and perigalacticon.
18
He, Jie, Peihua Qiu, Ka Young Park, Qinmei Xu et Michael Potegal. « Young Chinese children’s anger and distress ». International Journal of Behavioral Development 37, no 4 (28 mai 2013) : 349–56. http://dx.doi.org/10.1177/0165025413477006.
Texte intégralRésumé :
A hierarchical cluster analysis of the time course of the videotaped reactions of 75 Chinese 2–4-year olds to mothers’ toy-removal identified Distress, Low Anger, and High Anger behavior clusters. Anger often begins at low intensity; some children then escalate. The face-validity of Low and High Anger-cluster classifications was supported in that High Anger was displayed by a subset of the children who had first showed Low Anger. The three clusters had different and interpretable correlations with mothers’ temperament ratings. Developmentally, 2-year-olds displayed more Distress, including crying; 3-year-olds showed more Low Anger, including stamp-jump. While Low Anger is predominant during toy-removal in Chinese children, it is, contrastingly, the least-frequent component in the tantrums of North American children.
19
Leisawitz, D., et F. Bash. « A survey of molecular clouds associated by young open star clusters ». Symposium - International Astronomical Union 106 (1985) : 343–44. http://dx.doi.org/10.1017/s0074180900242757.
Texte intégralRésumé :
A major study of the molecular gas surrounding young star clusters is underway. We are using the Columbia University 1.2–m millimeter-wave telescope to observe emission from the J=1→0 rotation transition of 12CO in the vicinities of 128 open star clusters. The survey region around each cluster is at least 10 cluster diameters in size, typically ≳ 5 square degrees. Sensitivity is sufficient to detect lines as weak as 1 K over a range in velocity ± 83 km/s centered on the cluster velocity and with a velocity resolution of 0.65 km/s. Clusters in this sample have well-determined distances ranging from 1 to 5 kpc, and ages ≳ 100 million years (Myr).
20
Mengel, Sabine, Matthew D. Lehnert, Niranjan Thatte et Reinhard Genzel. « IFS and IR Observations of Star Clusters in the Antennae ». Symposium - International Astronomical Union 207 (2002) : 378–82. http://dx.doi.org/10.1017/s007418090022408x.
Texte intégralRésumé :
Over the past decade, it has become clear that interaction induced formation of compact young star clusters is a ubiquitous pheonomenon, and the understanding of this process is thought to also shed light on galaxy evolution in general, because these young clusters are widely believed to be the progenitors of a part of the globular cluster systems seen in local elliptical galaxies. We have observed the prototypical merger NGC 4038/4039 using near-infrared broad- and narrow band imaging, integral field spectroscopy and medium and high resolution spectroscopy. We find that all of the bright star clusters are young (<20 Myrs), but the “overlap region” hosts the youngest clusters (∼5 Myrs), while the nuclear starbursts started ∼100 Myrs ago. Photometric and dynamical masses range from 105 to a few x106M⊙. However, mass-to-light ratios vary from cluster to cluster and suggest differences in the contribution of low-mass stars. While clusters with a deficiency in low-mass stars are likely to evaporate before they are a Hubble time old, those with a high mass-to-light-ratio could represent young globulars.
21
Maíz-Apellániz, Jesus, et Nolan R. Walborn. « Massive Young Clusters in Nearby Galaxies ». Symposium - International Astronomical Union 205 (2001) : 222–23. http://dx.doi.org/10.1017/s0074180900221037.
Texte intégralRésumé :
We study the size distribution of massive young clusters (MYCs) and of the cavities around them. We discuss the existence of two cluster populations and we find evidences for molecular cloud confinement in the early stages of development.
22
Mauluddi, Hasbi Assidiki. « TIPOLOGI MINAT ANAK MUDA TERHADAP LEMBAGA KEUANGAN MIKRO SYARIAH BERDASARKAN LAYANAN MOBILE BANKING ». INTERNAL (Information System Journal) 1, no 2 (15 février 2019) : 1–10. http://dx.doi.org/10.32627/internal.v1i2.48.
Texte intégralRésumé :
This research was conducted to find out typical interest among young people towards Islamic microfinance institutions (LKMS) based on mobile banking services. The research data was taken by purposive sampling method on high school students in Kabupaten Bandung as many as 120 people. The data obtained is then processed using K-means cluster analysis. The results of the study show that the majority of young people in rural areas are interested in becoming customers of Islamic microfinance institutions (LKMS). This is due to the strong attractiveness of LKMS products, satisfaction using LKMS mobile banking applications, knowledge of LKMS institutions, and knowledge of LKMS products. The majority of these youth are members of cluster 2. While cluster members 1 and cluster 3 are minority clusters. In the minority clusters, weak knowledge of LKMS institutions and products causes a weak interest in young people in the use of LKMS mobile banking applications. This is not the case in cluster 2. Thus, the strong interest of young people in the application of Mobile banking LKMS membership is closely related to their knowledge of LKMS institutions and products.
23
Mauluddi, Hasbi Assidiki. « TIPOLOGI MINAT ANAK MUDA TERHADAP LEMBAGA KEUANGAN MIKRO SYARIAH BERDASARKAN LAYANAN MOBILE BANKING ». INTERNAL (Information System Journal) 1, no 2 (15 février 2019) : 1–10. http://dx.doi.org/10.32627/internal.v1i2.318.
Texte intégralRésumé :
This research was conducted to find out typical interest among young people towards Islamic microfinance institutions (LKMS) based on mobile banking services. The research data was taken by purposive sampling method on high school students in Kabupaten Bandung as many as 120 people. The data obtained is then processed using K-means cluster analysis. The results of the study show that the majority of young people in rural areas are interested in becoming customers of Islamic microfinance institutions (LKMS). This is due to the strong attractiveness of LKMS products, satisfaction using LKMS mobile banking applications, knowledge of LKMS institutions, and knowledge of LKMS products. The majority of these youth are members of cluster 2. While cluster members 1 and cluster 3 are minority clusters. In the minority clusters, weak knowledge of LKMS institutions and products causes a weak interest in young people in the use of LKMS mobile banking applications. This is not the case in cluster 2. Thus, the strong interest of young people in the application of Mobile banking LKMS membership is closely related to their knowledge of LKMS institutions and products.
24
Thongprayoon, Charat, Yeshwanter Radhakrishnan, Caroline C. Jadlowiec, Shennen A. Mao, Michael A. Mao, Pradeep Vaitla, Prakrati C. Acharya et al. « Characteristics of Kidney Recipients of High Kidney Donor Profile Index Kidneys as Identified by Machine Learning Consensus Clustering ». Journal of Personalized Medicine 12, no 12 (1 décembre 2022) : 1992. http://dx.doi.org/10.3390/jpm12121992.
Texte intégralRésumé :
Background: Our study aimed to characterize kidney transplant recipients who received high kidney donor profile index (KDPI) kidneys using unsupervised machine learning approach. Methods: We used the OPTN/UNOS database from 2010 to 2019 to perform consensus cluster analysis based on recipient-, donor-, and transplant-related characteristics in 8935 kidney transplant recipients from deceased donors with KDPI ≥ 85%. We identified each cluster’s key characteristics using the standardized mean difference of >0.3. We compared the posttransplant outcomes among the assigned clusters. Results: Consensus cluster analysis identified 6 clinically distinct clusters of kidney transplant recipients from donors with high KDPI. Cluster 1 was characterized by young, black, hypertensive, non-diabetic patients who were on dialysis for more than 3 years before receiving kidney transplant from black donors; cluster 2 by elderly, white, non-diabetic patients who had preemptive kidney transplant or were on dialysis less than 3 years before receiving kidney transplant from older white donors; cluster 3 by young, non-diabetic, retransplant patients; cluster 4 by young, non-obese, non-diabetic patients who received dual kidney transplant from pediatric, black, non-hypertensive non-ECD deceased donors; cluster 5 by low number of HLA mismatch; cluster 6 by diabetes mellitus. Cluster 4 had the best patient survival, whereas cluster 3 had the worst patient survival. Cluster 2 had the best death-censored graft survival, whereas cluster 4 and cluster 3 had the worst death-censored graft survival at 1 and 5 years, respectively. Cluster 2 and cluster 4 had the best overall graft survival at 1 and 5 years, respectively, whereas cluster 3 had the worst overall graft survival. Conclusions: Unsupervised machine learning approach kidney transplant recipients from donors with high KDPI based on their pattern of clinical characteristics into 6 clinically distinct clusters.
25
Herbig, G. H., et S. E. Dahm. « The Young Cluster IC 5146 ». Astronomical Journal 123, no 1 (janvier 2002) : 304–27. http://dx.doi.org/10.1086/324638.
Texte intégral
26
Herbig, G. H. « The Young Cluster IC 348 ». Astrophysical Journal 497, no 2 (20 avril 1998) : 736–58. http://dx.doi.org/10.1086/305500.
Texte intégral
27
Dahm, S. E. « The Young Cluster NGC 2362 ». Astronomical Journal 130, no 4 (octobre 2005) : 1805–28. http://dx.doi.org/10.1086/433178.
Texte intégral
28
Pfalzner, S. « Universality of young cluster sequences ». Astronomy & ; Astrophysics 498, no 2 (8 avril 2009) : L37—L40. http://dx.doi.org/10.1051/0004-6361/200912056.
Texte intégral
29
Bate, Matthew R., et Ian A. Bonnell. « Theory of Young Clusters ». Symposium - International Astronomical Union 221 (2004) : 257–64. http://dx.doi.org/10.1017/s0074180900241661.
Texte intégralRésumé :
We review recent results from hydrodynamical calculations of the formation of young stellar clusters. The calculations present a highly dynamical picture of star formation where the mass function of stars originates from competitive accretion between protostars and dynamical ejections which halt accretion. Large star clusters form hierarchically; a molecular cloud forms many small clusters that later merge into one large cluster, erasing the initial substructure. Using calculations that resolve fragmentation down to the opacity limit, we examine the implications of dynamical star formation for the IMF, the formation of brown dwarfs and close binaries, and the sizes of protoplanetary discs. Finally, we discuss the dependence of the results on the initial conditions.
30
Parmentier, Geneviève. « Early dynamical evolution of star cluster systems ». Proceedings of the International Astronomical Union 5, S266 (août 2009) : 87–94. http://dx.doi.org/10.1017/s1743921309990913.
Texte intégralRésumé :
AbstractViolent relaxation, the protocluster dynamical response to the expulsion of its residual star-forming gas, is a short albeit crucial episode in the evolution of star clusters and star cluster systems. Because it is heavily driven by cluster-formation and environmental conditions, it is a potentially highly rewarding phase in terms of probing star formation and galaxy evolution. In this contribution, I review how cluster-formation and environmental conditions affect the shape of the young cluster mass function and the relation between the present star-formation rate of galaxies and the mass of their young, most massive cluster.
31
de Grijs, Richard. « Young massive star clusters : achievements and challenges ». Proceedings of the International Astronomical Union 5, S266 (août 2009) : 49–57. http://dx.doi.org/10.1017/s174392130999086x.
Texte intégralRésumé :
AbstractIn spite of significant recent and ongoing research efforts, most of the early evolution and long-term fate of young massive star clusters remain clouded in uncertainties. Here, I discuss our understanding of the initial conditions of star cluster formation and the importance of initial substructure for the subsequent dynamical-evolution and mass-segregation timescales. I also assess our current understanding of the (initial) binary fraction in star clusters and the shape of the stellar initial mass function at the low-mass end in the low-metallicity environment of the Large Magellanic Cloud. Finally, I question the validity of our assumptions leading to dynamical cluster mass estimates. I conclude that it seems imperative that observers, modellers and theorists combine efforts and exchange ideas and data freely for the field to make a major leap forward.
32
Cabrera-Ziri, I., N. Bastian, B. Davies, G. Magris, G. Bruzual et F. Schweizer. « Constraining globular cluster formation through studies of young massive clusters - II. A single stellar population young massive cluster in NGC 34 ». Monthly Notices of the Royal Astronomical Society 441, no 3 (26 mai 2014) : 2754–59. http://dx.doi.org/10.1093/mnras/stu764.
Texte intégral
33
Hron, J., et H. M. Maitzen. « Young galactic clusters and the rotation curve of our Galaxy ». Symposium - International Astronomical Union 106 (1985) : 105–6. http://dx.doi.org/10.1017/s0074180900242150.
Texte intégralRésumé :
The most recent determination of Oort's galactic rotation constant ‘A’ from open clusters was made by Taff and Littleton (1972). They obtained A=15 km/s/kpc, but unfortunately they omitted a detailed description of their cluster sample. For the present work we compiled a catalogue of O-B3 clusters for which radial velocities and distances are available. The individual cluster references given by Janes and Adler (1982) have been used to find best distances for the clusters. Radial velocities were taken from the list of Dr. Wramdemark (private communication) and from Hron et al. (1984). The catalogue contains 105 clusters distributed over the four galactic quadrants as 16:27:35:27.
34
Sirianni, Marco, Antonella Nota, Guido De Marchi, Claus Leitherer et Mark Clampin. « Mass Segregation in the Young SMC Cluster NGC 330 ». Symposium - International Astronomical Union 207 (2002) : 687–90. http://dx.doi.org/10.1017/s0074180900224558.
Texte intégralRésumé :
We present a new study of the low end of the stellar IMF of NGC 330, the richest young star cluster in the Small Magellanic Cloud (SMC). Using deep broadband images taken with the HST/WFPC2 we have derived the cluster's luminosity function and constructed the initial mass function (IMF) in the mass range 1 − 7M⊙. We have investigated the IMF as a function of the radial distance from the cluster center. We find that, after correction for background contamination, the IMF is fairly homogeneous with a slope slightly steeper than Salpeter's in the central regions of the cluster (< 40″) but becomes increasingly steeper with distance, indicating a preponderance of massive stars in the core of the cluster. NGC 330 is one of the first clusters for which evidence of mass segregation is directly found.
35
Santiago-Cortés, M., Y. D. Mayya et D. Rosa-González. « Study of the young and old compact stellar cluster population in M81 ». Proceedings of the International Astronomical Union 5, S266 (août 2009) : 532. http://dx.doi.org/10.1017/s1743921309991955.
Texte intégralRésumé :
AbstractWe study the population of compact stellar clusters in M 81 using the HST/ACS images in the filters F435W, F606W and F814W that cover a total field of view of approximately 340 square arcmin, the largest area covered to date for this galaxy. We present details about the selection criteria, which were based on both morphological and photometrical features. The extracted sample of compact stellar clusters shows the presence of two cluster populations, a blue cluster group (young) with more than 300 objects, and a red cluster group (old) containing 138 objects. Surprisingly, the young group lacks clusters more massive than 10 000 M⊙ which are present in large numbers in its neighbor M 82. The luminosity function of the young group follows a power-law distribution with an index of 2.0. The luminosity function of the red group closely resembles that of the globular clusters in the Milky Way. Assuming an age of 5 Gyr, these red clusters have masses between 0.1 and 10 × 106 M⊙.
36
Wang, C. K. John, et Stuart J. H. Biddle. « Young People’s Motivational Profiles in Physical Activity : A Cluster Analysis ». Journal of Sport and Exercise Psychology 23, no 1 (mars 2001) : 1–22. http://dx.doi.org/10.1123/jsep.23.1.1.
Texte intégralRésumé :
A great deal has been written about the motivation of young people in physical activity, and the determinants of activity for this age group have been identified as a research priority. Despite this, there are few large-scale studies identifying “types” or “clusters” of young people based on their scores on validated motivation inventories. This study reports the results of a cluster analysis of a large national sample (n = 2,510) of 12- to 15-year-olds using contemporary approaches to physical activity motivation: achievement goal orientations, self-determination theory (including amotivation), the nature of athletic ability beliefs, and perceived competence. Five meaningful clusters were identified reflecting two highly motivated and two less well-motivated clusters, as well as a clearly amotivated cluster. Groupings were validated by investigating differences in physical activity participation and perceptions of physical self-worth. Some clusters reflected age and gender differences. The results provide valuable information for likely strategies to promote physical activity in young people.
37
Hußmann, Benjamin, Andrea Stolte et Wolfgang Brandner. « Proper-motion measurements in the Quintuplet cluster ». Proceedings of the International Astronomical Union 5, S266 (août 2009) : 422. http://dx.doi.org/10.1017/s174392130999158x.
Texte intégralRésumé :
AbstractThe three young, massive star clusters found in the Galactic Centre region (Young Nuclear Cluster, the Arches and Quintuplet clusters) are among the six most massive star clusters in our Galaxy, with masses similar to low-mass, extragalactic starburst clusters. The conditions for star formation in this region are extreme and likely comparable to those found in the Hii regions in starburst galaxies and tidal-interaction zones of mergers. As the inner Galactic star clusters can be resolved, they can serve as templates for extragalactic starburst clusters. With knowledge of the spectral types, masses and ages of the individual stars, their stellar population can be studied in detail, allowing derivation of their present-day mass function (PDMF). The Quintuplet cluster, with an age of about 4 Myr, is the most extended of the three clusters and also displays a lower spatial density. To determine its mass function correctly, the distinction between cluster and field stars is therefore of particular importance. We present the first determination of a proper-motion-membership sample for the Quintuplet cluster. By comparing two high-precision astrometric VLT/NACO data sets with a time baseline of 5 years, the displacement of the Quintuplet cluster relative to the field population was measured and a selection of the proper-motion cluster members could be established, from which the PDMF can be derived.
38
Wünsch, Richard, Jan Palouš, Guillermo Tenorio-Tagle, Casiana Muñoz-Tuñón et Soňa Ehlerová. « Bimodal regime in young massive clusters leading to subsequent stellar generations ». Proceedings of the International Astronomical Union 12, S316 (août 2015) : 294–301. http://dx.doi.org/10.1017/s1743921315009023.
Texte intégralRésumé :
AbstractMassive stars in young massive clusters insert tremendous amounts of mass and energy into their surroundings in the form of stellar winds and supernova ejecta. Mutual shock-shock collisions lead to formation of hot gas, filling the volume of the cluster. The pressure of this gas then drives a powerful cluster wind. However, it has been shown that if the cluster is massive and dense enough, it can evolve in the so–called bimodal regime, in which the hot gas inside the cluster becomes thermally unstable and forms dense clumps which are trapped inside the cluster by its gravity. We will review works on the bimodal regime and discuss the implications for the formation of subsequent stellar generations. The mass accumulates inside the cluster and as soon as a high enough column density is reached, the interior of the clumps becomes self-shielded against the ionising radiation of stars and the clumps collapse and form new stars. The second stellar generation will be enriched by products of stellar evolution from the first generation, and will be concentrated near the cluster center.
39
Turner, Jean L., et Sara C. Beck. « Watching the Birth of Super Star Clusters ». Symposium - International Astronomical Union 221 (2004) : 125–30. http://dx.doi.org/10.1017/s0074180900241521.
Texte intégralRésumé :
Subarcsecond infrared and radio observations yield important information about the formation of super star clusters from their surrounding gas. We discuss the general properties of ionized and molecular gas near young, forming SSCs, as illustrated by the prototypical young, forming super star cluster nebula in the dwarf galaxy NGC 5253. This super star cluster appears to have a gravitationally bound nebula, and the lack of molecular gas suggests a very high star formation efficiency, consistent with the formation of a large, bound cluster.
40
Gouliermis, Dimitrios A., et Sacha Hony. « NGC 346 : Looking in the Cradle of a Massive Star Cluster ». Proceedings of the International Astronomical Union 12, S316 (août 2015) : 117–22. http://dx.doi.org/10.1017/s1743921316008759.
Texte intégralRésumé :
AbstractHow does a star cluster of more than few 10,000 solar masses form? We present the case of the cluster NGC 346 in the Small Magellanic Cloud, still embedded in its natal star-forming region N66, and we propose a scenario for its formation, based on observations of the rich stellar populations in the region. Young massive clusters host a high fraction of early-type stars, indicating an extremely high star formation efficiency. The Milky Way galaxy hosts several young massive clusters that fill the gap between young low-mass open clusters and old massive globular clusters. Only a handful, though, are young enough to study their formation. Moreover, the investigation of their gaseous natal environments suffers from contamination by the Galactic disk. Young massive clusters are very abundant in distant starburst and interacting galaxies, but the distance of their hosting galaxies do not also allow a detailed analysis of their formation. The Magellanic Clouds, on the other hand, host young massive clusters in a wide range of ages with the youngest being still embedded in their giant HII regions. Hubble Space Telescope imaging of such star-forming complexes provide a stellar sampling with a high dynamic range in stellar masses, allowing the detailed study of star formation at scales typical for molecular clouds. Our cluster analysis on the distribution of newly-born stars in N66 shows that star formation in the region proceeds in a clumpy hierarchical fashion, leading to the formation of both a dominant young massive cluster, hosting about half of the observed pre–main-sequence population, and a self-similar dispersed distribution of the remaining stars. We investigate the correlation between stellar surface density (and star formation rate derived from star-counts) and molecular gas surface density (derived from dust column density) in order to unravel the physical conditions that gave birth to NGC 346. A power law fit to the data yields a steep correlation between these two parameters with a considerable scatter. The fraction of stellar over the total (gas plus young stars) mass is found to be systematically higher within the central 15 pc (where the young massive cluster is located) than outside, which suggests variations in the star formation efficiency within the same star-forming complex. This trend possibly reflects a change of star formation efficiency in N66 between clustered and non-clustered star formation. Our findings suggest that the formation of NGC 346 is the combined result of star formation regulated by turbulence and of early dynamical evolution induced by the gravitational potential of the dense interstellar medium.
41
Grosbøl, Preben, et Horacio Dottori. « Comparing ALMA, VLT, and HST data for Massive, Young Clusters in Grand-Design Spirals ». Proceedings of the International Astronomical Union 12, S316 (août 2015) : 141–42. http://dx.doi.org/10.1017/s1743921316007080.
Texte intégralRésumé :
AbstractA population of young, massive stellar cluster complexes with near-infrared (NIR) colors indicating high extinction (i.e. Av ~ 7m) was identified on HAWK-I/VLT images of several nearby, grand-design spiral galaxies. Models suggest that they are very young cluster complexes still embedded in a dust/gas envelope which will be expelled after 5-7 Myr. This type of very young, embedded clusters are not seen in optical studies using HST data.A detailed comparison of HST and HAWK-I images was done to better understand the discrepancy between the optical and NIR detection of stellar clusters in nearby galaxies. More than 70% of the NIR clusters are located close to dust lanes which would make an optical detection difficult. A comparison of the ALMA CO(1-0)-map of NGC 4321 and the young, massive clusters shows that 60% of them have CO emission within 2“ indicating a correlation between giant molecular clouds and formation of massive clusters.
42
Larsen, Søren S. « Young and intermediate-age massive star clusters ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 368, no 1913 (28 février 2010) : 867–87. http://dx.doi.org/10.1098/rsta.2009.0255.
Texte intégralRésumé :
An overview of our current understanding of the formation and evolution of star clusters is given, with the main emphasis on high-mass clusters. Clusters form deeply embedded within dense clouds of molecular gas. Left-over gas is cleared within a few million years and, depending on the efficiency of star formation, the clusters may disperse almost immediately or remain gravitationally bound. Current evidence suggests that a small percentage of star formation occurs in clusters that remain bound, although it is not yet clear whether this fraction is truly universal. Internal two-body relaxation and external shocks will lead to further, gradual dissolution on time scales of up to a few hundred million years for low-mass open clusters in the Milky Way, while the most massive clusters (>10 5 M ⊙ ) have lifetimes comparable to or exceeding the age of the Universe. The low-mass end of the initial cluster mass function is well approximated by a power-law distribution, , but there is mounting evidence that quiescent spiral discs form relatively few clusters with masses M >2×10 5 M ⊙ . In starburst galaxies and old globular cluster systems, this limit appears to be higher, at least several ×10 6 M ⊙ . The difference is likely related to the higher gas densities and pressures in starburst galaxies, which allow denser, more massive giant molecular clouds to form. Low-mass clusters may thus trace star formation quite universally, while the more long-lived, massive clusters appear to form preferentially in the context of violent star formation.
43
Braden, Ella K., Robert D. Mathieu et Sören Meibom. « Defining the Binary Star Population in the Young Open Cluster M35 (NGC 2168) ». Proceedings of the International Astronomical Union 3, S246 (septembre 2007) : 105–6. http://dx.doi.org/10.1017/s1743921308015391.
Texte intégralRésumé :
AbstractWe present current results from the ongoing WIYN Open Cluster Study radial-velocity survey for 1410 stars in the young (150 Myr) open cluster M35 (NGC 2168) and establish a benchmark for initial conditions in young open clusters. We find for periods ≲ 1000 days a minimum binary frequency of 0.36 – 0.51. We also analyze the spatial, period and eccentricity distributions of the binary systems and find that the period and eccentricity distributions are well approximated by scaled field distributions from Duquennoy & Mayor (1991). With our large sample size and long baseline, we have a unique understanding of the binary population in this young cluster, making it ideal for defining initial conditions for dynamical simulations.
44
Yeh, Sherry C. C., Chao-Wei Tsai, Thomas R. Geballe et Cinthya N. Herrera. « Mid-infrared [NeII] Imaging of Young Massive Star Clusters Near Galactic Nuclei ». Proceedings of the International Astronomical Union 12, S316 (août 2015) : 161–62. http://dx.doi.org/10.1017/s1743921316008711.
Texte intégralRésumé :
AbstractWe investigate the formation of young massive clusters near the nuclei in NGC 6946, IC 342, Maffei II, and NGC 7714, using ground-based mid-infrared [NeII] imaging. We derive the cluster formation efficiency and cluster mass function, and the results suggest that environmental effects on YMC formation may not be significant.
45
Kontizas, M., D. Gouliermis et E. Kontizas. « Central Densities of Star Clusters in the Magellanic Clouds ». Symposium - International Astronomical Union 174 (1996) : 335–36. http://dx.doi.org/10.1017/s0074180900001698.
Texte intégralRésumé :
The way star cluster systems in galaxies are forming and survive seem to depend on the relation of the central density ρ (at half mass radius) of each cluster with its galactocentric distance Rgc. It is found that this relation takes the form of: The cluster systems of our Galaxy and of the two Magellanic Clouds, have been investigated. We have taken the cluster system of the conventional globulars of our Galaxy whereas the young and old systems of clusters in the LMC and SMC were treated separately. The radial distributions of central densities and half mass radii were found for all these systems showing a definite trend which depends on: (α) The total mass of the parent galaxy & (β) The age of the cluster system (young - old). It therefore appears that the total mass and/or the morphology of the parent galaxy plays a major role on the loci where clusters survive and form.
46
Elmegreen, Bruce G. « The nature and nurture of star clusters ». Proceedings of the International Astronomical Union 5, S266 (août 2009) : 3–13. http://dx.doi.org/10.1017/s1743921309990809.
Texte intégralRésumé :
AbstractStar clusters have hierarchical patterns in space and time, suggesting formation processes in the densest regions of a turbulent interstellar medium. Clusters also have hierarchical substructure when they are young, which makes them all look like the inner mixed parts of a pervasive stellar hierarchy. Young field stars share this distribution, presumably because some of them came from dissolved clusters and others formed in a dispersed fashion in the same gas. The fraction of star formation that ends up in clusters is apparently not constant, but may increase with interstellar pressure. Hierarchical structure explains why stars form in clusters and why many of these clusters are self-bound. It also explains the cluster mass function. Halo globular clusters share many properties of disk clusters, including what appears to be an upper cluster cutoff mass. However, halo globulars are self-enriched and often connected with dwarf galaxy streams. The mass function of halo globulars could have initially been like the power-law mass function of disk clusters, but the halo globulars have lost their low-mass members. The reasons for this loss are not understood. It could have happened slowly over time as a result of cluster evaporation, or it could have happened early after cluster formation as a result of gas loss. The latter model explains best the observation that the globular cluster mass function has no radial gradient in galaxies.
47
Li, Hui, Oleg Y. Gnedin, Nickolay Y. Gnedin, Xi Meng, Vadim A. Semenov et Andrey V. Kravtsov. « STAR CLUSTER FORMATION IN COSMOLOGICAL SIMULATIONS. I. PROPERTIES OF YOUNG CLUSTERS ». Astrophysical Journal 834, no 1 (3 janvier 2017) : 69. http://dx.doi.org/10.3847/1538-4357/834/1/69.
Texte intégral
48
Harris, William E. « Young, old, massive : Steps to understanding globular cluster formation ». Proceedings of the International Astronomical Union 14, S351 (mai 2019) : 3–12. http://dx.doi.org/10.1017/s1743921319006495.
Texte intégralRésumé :
AbstractOn observational grounds we now know a huge amount about the characteristics of massive star clusters in galaxies of all types, from the smallest dwarfs to the most massive giants and even into the Intracluster Medium. The old globular clusters (GCs) in particular exhibit a high degree of uniformity across all these environments in their physical properties including scale size, luminosity distribution, metallicity distribution, and age. As survivors of a long period of dynamical evolution, they are “unusual, but not special” among star clusters.The past few years have seen major advances in theoretical modelling that are starting to reveal how these massive star clusters formed in the early stages of galaxy evolution. Several suites of models point to their emergence in GMCs (Giant Molecular Clouds), which provide the turbulent big reservoirs of gas within which star clusters can be built. At cluster masses ∼105M⊙ and above, clusters form hierarchically through a nearly equal combination of direct gas accretion, and mergers with smaller clusters scattered throughout the GMC. GCs and YMCs (young massive clusters) in this high mass range should therefore be composite systems right from birth. To make such high-mass clusters, host GMCs of ∼107M⊙ are needed, and these are most commonly found in galaxies at redshifts z ≳ 2.
49
Hamraz, E., R. F. Peletier, H. G. Khosroshahi, E. A. Valentijn, M. den Brok et A. Venhola. « Young stellar populations in early-type dwarf galaxies ». Astronomy & ; Astrophysics 625 (mai 2019) : A94. http://dx.doi.org/10.1051/0004-6361/201935076.
Texte intégralRésumé :
Aims. To understand the stellar population content of early-type dwarf galaxies (dEs) and their environmental dependence, we compare the slopes and intrinsic scatter of color–magnitude relations (CMRs) for three nearby clusters, Fornax, Virgo, and Coma. Additionally, we present and compare internal color profiles of these galaxies to identify central blue regions with younger stars. Methods. We use the imaging of the HST/ACS Fornax cluster in the magnitude range of −18.7 ≤ Mg′ ≤ −16.0 to derive magnitudes, colors, and color profiles, which we compare with literature measurements from the HST/ACS Virgo and Coma Cluster Survey. We take advantage of HST accuracy to investigate and parameterize the (g′−z′) color profiles of these dEs. Results. Based on analysis of the color profiles, we report on a large number of dEs with young stellar populations at their center in all three clusters. While for Virgo and Coma the number of blue-cored dEs is found to be 85%±2% and 53%±3%, respectively, for Fornax, we find that all galaxies have a blue core. We show that bluer cores reside in fainter dEs, similar to the trend seen in nucleated dEs. We find no correlation between the luminosity of the galaxy and the size of its blue core. Moreover, a comparison of the CMRs of the three clusters shows that the scatter in the CMR of Virgo is considerably larger than in the Fornax and Coma clusters. Presenting adaptive smoothing we show that the galaxies on the blue side of the CMR often show evidence for dust extinction, which strengthens the interpretation that the bluer colors are due to young stellar populations. We also find that outliers on the red side of the CMR are more compact than what is expected for their luminosity. We find several of these red outliers in Virgo, often close to more massive galaxies. No red outlying compact early-types are found in Fornax and Coma in this magnitude range while we find three in the Virgo cluster. We show that the CMR of the Fornax and Virgo clusters are slightly bluer than that of Coma. We suggest that the large number of outliers and larger scatter found for Virgo CMR are a result of the alternative assembly history of this cluster.
50
Krzesinski, J. « Search for Pulsational Instability among h Persei Stars ». International Astronomical Union Colloquium 155 (1995) : 299–300. http://dx.doi.org/10.1017/s0252921100037192.
Texte intégralRésumé :
AbstractThe northern-hemisphere double cluster h and χ Persei is one of the richest young open clusters. At least half of the brightest stars in the cluster appear to be variables and most of them axe Be stars. Till now there was no evidence for the presence of β Cephei stars in the cluster. It is remarkable that the similar age southern cluster NGC 3293 and other clusters belonging to the same age group are documented as clusters in which β Cephei stars have been observed. In this work we report finding one suspected β Cephei-like object, basing on our own observations.