1,721,024 research outputs found
CaTaclysm in the SMC - star clusters vs. field stars
No full textWe present new results based on VLT Ca Triplet (CaT) medium resolution spectroscopy of some 200 red giantmembers of 29 SMC intermediate - old age clusters. We derive mean cluster velocities to a few km/s and mean metallicities to 0.05 dex. We also derive accurate velocities and metallicities for about 750 surrounding field giants. We investigate the metallicity distribution, age-metallicity relation and metallicity gradient in great detail for the SMC using this large and homogeneous database. We find a number of interesting results and some surprising differences between the clusters and fields. The clusters display a likely bimodal metallicity distribution while the field stars are unimodal. The clusters show no strong evidence of a metallicity gradient while the field stars show a strong negative gradient in the inner region of the galaxy that appears to reverse sign in the outer region. The difference between the cluster metallicity and the mean of the surrounding field stars is a strong function of the cluster metallicity. The age-metallicity relation of the clusters shows a significant intrinsic metallicity dispersion at all ages, and no satisfactory fit to any current chemical evolution model. We discuss these results and their implications for the formation and evolution of the SMC
Two newly identified, relatively old star clusters in the Small Magellanic Cloud
Get PDFWe present the results on the age and metallicity estimates of the Small Magellanic Cloud (SMC) clusters L110, L112 and L113 obtained from CCD Washington CT1 photometry. We confirm L113 as a relatively old and metal-poor cluster, and report for the first time that L110 and 112 are also relatively old clusters (t ~ 6.5 Gyr). Their derived ages and metallicities reinforce previous suggestions that the farther a cluster is from the centre of the galaxy, the older and more metal-poor it is, with some dispersion. In addition, the bursting star formation model still appears to be the most probable paradigm to describe the SMC´s star formation history. We call attention to a second possible burst at ~6-7 Gyr, besides the known burst at ~3 Gyr.Fil: Piatti, Andres Eduardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Sarajedini, Ata. University of Florida; Estados UnidosFil: Geisler, Doug. Universidad de Concepción; ChileFil: Gallart, Carme. Instituto de Astrof´ısica de Canarias; EspañaFil: Wischnjewsky, Marina
Young star clusters immersed in intermediate-age fields in the Small Magellanic Cloud
Get PDFWe present CCD photometry in the Washington C and T1 filters for six star clusters (B 34, NGC 256, NGC 265, NGC 294, IC 1611 and NGC 376) in the Small Magellanic Cloud (SMC) and their surrounding fields. The resultant colour–magnitude diagrams (CMDs) extend from T1∼ 14 to as faint as T1∼ 22 revealing the main-sequence turnoffs of the clusters. Adopting a metallicity of Z= 0.004, we compare our cluster photometry with theoretical isochrones in the Washington system in order to derive ages. To facilitate age determination of the surrounding fields, we use the magnitude difference between the helium-burning red clump stars and the main-sequence turnoff. Finally, we estimate mean metallicities for the field stars by comparing the location of the field red giant branch with standard giant branches for Galactic globular clusters of known abundance, corrected for age effects. Combining these results with our previous work, we find a clear trend of younger clusters being located closer to the centre of the SMC. In addition, there is a tendency for the mean metallicity and its dispersion to be greater inside 4° of the SMC's centre as compared to outside this radius. As far as the properties of the field stars are concerned, we find little correlation between the ages of the clusters and those of the field stars against which they are projected. Clearly, more work needs to be done to clarify these trends.Fil: Piatti, Andres Eduardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Sarajedini, Ata. University of Florida; Estados UnidosFil: Geisler, Doug. Universidad de Concepción; ChileFil: Clark, David. University of Florida; Estados UnidosFil: Seguel, Juan. Universidad de Concepción; Chil
Seven young star clusters in the inner region of the Small Magellanic Cloud
Get PDFWe present CCD photometry in the Washington system C and T1 passbands down to T1∼ 22 in the fields of L35, L45, L49, L50, L62, L63 and L85, seven poorly studied star clusters in the inner region of the Small Magellanic Cloud (SMC). We measured T1 magnitudes and C−T1 colours for a total of 114 826 stars distributed throughout cluster areas of 13.7 × 13.7 arcmin2 each. Cluster radii were estimated from star counts distributed throughout the entire observed fields. The seven clusters are generally characterized by a relatively small angular size and by a high field star contamination. We performed an in-depth analysis of the field star contamination of the colour–magnitude diagrams (CMDs), and statistically cleaned the cluster CMDs. Based on the best fits of isochrones computed by the Padova group to the (T1, C−T1) CMDs, we derive ages for the sample, assuming Z= 0.004, finding ages between 25 Myr and 1.2 Gyr. We then examined different relationships between positions in the SMC, age and metallicity of a larger sample of clusters including our previous work whose ages and metallicities are on the same scale used in this paper. We confirm previous results in the sense that the further a cluster is from the centre of the galaxy, the older and more metal poor it is, with some dispersion; although clusters associated with the Magellanic Bridge clearly do not obey the general trend. The number of clusters within ∼ 2° of the SMC centre appears to have increased substantially after ∼2.5 Gyr ago, hinting at a burst.Fil: Piatti, Andres Eduardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Geisler, Doug. Universidad de Concepción; ChileFil: Sarajedini, Ata. University of Florida; Estados UnidosFil: Gallart, Carme. Instituto de Astrof´ısica de Canarias; EspañaFil: Wischnjewsky, Marina. Universidad de Chile; Chil
Five young star clusters in the outer region of the Small Magellanic Cloud
Get PDFColour–magnitude diagrams in the Washington system are presented for the first time for five star clusters projected on to the outer region of the Small Magellanic Cloud (SMC). The clusters are found to have ages in the range 0.1–1.0 Gyr, as derived from the fit of isochrones with Z= 0.004. This sample increases substantially the number of young clusters in the outer SMC – particularly in the south-east quadrant – with well-derived parameters. We combine our results with those for other clusters in the literature to derive as large and homogeneous a data base as possible (totalling 49 clusters) in order to study global effects. We find no conclusive evidence for a dispersion in the cluster ages and metallicities as a function of their distance from the galaxy centre, in the SMC outer region. L 114 and 115, although very distant, are very young clusters, lying in the bridge of the SMC and therefore most likely formed during the interaction which formed this feature. We also find very good agreement between the cluster age–metallicity relation (AMR) and the prediction from a bursting model from Pagel & Tautvaišienė with a burst that occurred 3 Gyr ago. Comparing the present cluster AMR with that derived by Harris & Zaritsky for field stars in the main body of the SMC, we find that field stars and clusters underwent similar chemical enrichment histories during approximately the last couple of Gyr, but their chemical evolution was clearly different between 4 and 10 Gyr ago.Fil: Piatti, Andres Eduardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Sarajedini, Ata. University of Florida; Estados UnidosFil: Geisler, Doug. Universidad de Concepción; ChileFil: Gallart, Carme. Instituto de Astrofísica de Canarias; EspañaFil: Wischnjewsky, Marina. Universidad de Chile; Chil
Commission 37: Star Clusters and Associations
No full textResearch on star clusters and associations includes the observation and theory of stellar groupings as they form and evolve, cluster disruption, stellar interactions inside clusters, and star formation in dense environments. In what follows, we list past, present and future meetings (http://www2.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/meetings/), publications statistics and important surveys, reviews, and databases about clusters
The Acs Survey of Globular Clusters. V. Generating a Comprehensive Star Catalog for each Cluster
No full textThe ACS Survey of Globular Clusters has used Hubble Space Telescope's Wide-Field Channel to obtain uniform imaging of 65 of the nearest globular clusters to provide an extensive homogeneous data set for a broad range of scientific investigations. The survey goals required not only a uniform observing strategy, but also a uniform reduction strategy. To this end, we designed a sophisticated software program to process the cluster data in an automated way. The program identifies stars simultaneously in the multiple dithered exposures for each cluster and measures them using the best available point-spread function models. We describe here in detail the program's rationale, algorithms, and output. The routine was also designed to perform artificial-star tests, and we ran a standard set of ~105 tests for each cluster in the survey. The catalog described here will be exploited in a number of upcoming papers and will eventually be made available to the public via the World Wide Web.
Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555
Commission 37: Star Clusters and Associations
Get PDFThe business session for Commission 37 was held on 11 August 2009 at the IAU General Assembly in Rio de Janeiro. The meeting was attended by about a dozen members of our Comission, including President Elmegreen, VP Carraro and several committee members. We introduced ourselves and then went through a powerpoint presentation first prepared by outgoing President Hatzidimitriou and revised by incoming President Elmegreen. The contents of the powerpoint presentation are given in this summary
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