Cluster open clusters

Fig. 6. Initial fuel loading of PWR showiag the three enrichments where ( ) represents 3.10 wt % ( ) 2.60 ( ) 2.10 and (0) the cluster openings of...

For c/rwo-boranes and for the larger open-cluster boranes it becomes increasingly difficult to write a simple satisfactory localized orbital structure, and a full MO treatment is required. Intermediate cases, such a.s B5H9, require several resonance hybrids in the localized orbital... 

Wade stated some further rules for open clusters that are interpreted as deltahedra with missing vertices. They are of special importance for boranes ... 

Furthermore, it has been demonstrated that the successful electrocatalytic reduction of C02 with [Ru(bpy)2(CO)2]2+ in aqueous MeCN is mainly due to the formation of a polymeric electroactive film, which occurs during the reduction of the complex.91 This film is composed of an open cluster polymer [Ru(bpy)(CO)2]ra (Scheme 6) based upon extended Ru°—Ru° bonds. Electropolymerization of [Ru(bpy)2(CO)2]2+ results from the overall addition of two electrons per mole of [Ru(bpy)2(CO)2]2+ and is associated with the decoordination of one bpy ligand (Equation (33)). 

Ultimately, however, one seeks abundances from high-resolution spectroscopy, and a full elemental abundance analysis. Data on a broad range of elemental abundances in open clusters have been limited until recently. Fortunately, this situation is beginning to change. 

The most distant clusters in these samples reach to Galactocentric distances of 16 kpc, where [Fe/H] -0.5 to -0.6. Recently two open clusters have been... 

There has been mixed or inconclusive evidence for time variations in the gradient from open cluster data. Most studies that comment on the question ([5,10,6,11]) have shown slight evolution from steeper gradients in the past to more shallow ones, though the effect is at the level of only a few sigma. However,... 

Theoretical models of galactic chemical evolution offer varying predictions of how the gradient should change with time, so using open clusters to measure that time-dependence can provide important constraints on model parameters. 

For years, it has been known that some of the oldest open clusters, such as NGC 188, had roughly solar metallicity, but increasing samples have shown clearly that there is no relationship between overall cluster metallicity and age ([3,10,6,11]) in the solar neighborhood. The existence of clusters like NGC 6791, a 9 Gyr old cluster with metallicity twice solar, requires prompt initial enrichment of the Galactic disk, at least in the solar neighborhood. The metallicity of open clusters depends much more strongly on their position in the disk than on their age. 

Only recently have large numbers of open clusters become the subject of elemental abundance determinations other than those of the lightest elements (Li, C). A survey of the literature (not guaranteed to be complete), including some unpublished data kindly made available for this contribution, revealed [Fe/H] determinations for 45 open clusters. Of these, 33 have determinations of at least some of the a-elements, and these are collected in Table 1. There are very few clusters in common between studies, so it is not possible to investigate systematic differences between studies, nor to bring these measures to a common system. 

Unlike the field stars, the open clusters show enhanced values of [Na/Fe] ( 0.2) and [Al/Fe] ( 0.1). Sodium and aluminum seem to be high and show a large dispersion at all ages and Galactocentric distances. There is recent evidence that... 

Old Open Clusters as Tracers of Galactic Chemical Evolution the BOCCE Project... 

Open clusters (OCs) are important tools both for stellar and for galactic astrophysics, as tests of stellar evolution theory for low and intermediate mass stars and as tracers of the Galactic disk properties. Since old OCs allow us to probe the lifetime of the Milky Way disk, up to about 10 Gyr ago, they can be used to study the disk evolution with time, and in particular its chemical history. 

Abstract. In this contribution we present the results based on high-resolution spectra of 45 clump stars of the Galactic field. The main atmospheric parameters and abundances of 12C, 13C, N, O and other mixing sensitive chemical elements were investigated. Elemental ratios in the sample of field stars are compared to the results available for evolved stars in open clusters and to the theoretical prediction of extra mixing in stellar interiors. 

NGC2324 A Relatively Young, Metal-Poor Open Cluster Located Beyond the Perseus Spiral Arm... 

We present CCD photometry in the Johnson V, Kron-Cousins I and Washington system CTi passbands for NGC2324, a rich open cluster located near the Galactic anticentre direction. We believe that the high discrepancy in the basic cluster parameters derived in previous studies, particularly in the cluster metal content, warrants their redetermination on the basis of more reliable data. 

Studying Old Open Clusters with Detached Eclipsing Binaries... 

We are currently working on detached systems in the old open clusters NGC 2243, NGC 188 and NGC 6791. Presently we have the most complete and best data available for NGC 188 (see Fig. 1 and caption for more details) and NGC 2243. In both clusters the detached system is located close to the cluster turnoff and consists of two quite similar stars. In NGC 6791 we were able to determine the period for the system called V20 [1] and have subsequently obtained photometry for this system covering both eclipses. Due to the faintness (V = 17.34) we have not yet obtained radial velocities for the system which is comprised of a star very close to the cluster turnoff and a main-sequence star approximately 2.2 magnitudes (V) fainter. 

Abundance Variations in the Galactic Disk Planetary Nebulae, Open Clusters and Field Stars... 

Fig. 1. Oxygen abundances as a function of the activity index, Rx, derived from X-ray data (left-hand panels) and the excitation temperature Texc (right-hand panels). The bottom panels show the difference between [O/Fe] yielded by the OI triplet at about 7774 A and the [OI] A6300 line. Filled circles RS CVn binaries ([2] and [3]), filled squares field subgiants [3], filled triangles Pleiades stars, open triangles Hyades stars, open circles, squares and hexagons disk dwarfs. The source of the literature data for the open cluster and Galactic disk stars can be found in [4].

P. North, F. Royer, C. Melo et al. New homogeneous vsinf determinations for B stars in galactic open clusters . In Stellar Rotation, IAIJ Symp. 215, ed. by A. Maeder, P. Eenens (in press)... 

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