Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
New catalogue of blue stragglers in open clusters
We present a catalogue of blue-straggler candidates in galactic openclusters. It is based on the inspection of the colour-magnitude diagramsof the clusters, and it updates and supersedesthe first version(Ahumada & Lapasset 1995). A new bibliographical search was made foreach cluster, and the resulting information is organised into twotables. Some methodological aspects have been revised, in particularthose concerning the delimitation of the area in the diagrams where thestragglers are selected.A total of 1887 blue-straggler candidates have been found in 427 openclusters of all ages, doubling the original number. The catalogued starsare classified into two categories mainly according to membershipinformation.The whole catalogue (Tables 8, 9, notes, and references) is onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/463/789
| CCD photometric search for peculiar stars in open clusters. VIII. King 21, NGC 3293, NGC 5999, NGC 6802, NGC 6830, Ruprecht 44, Ruprecht 115, and Ruprecht 120
Context: We continue our survey of magnetic chemically peculiar (CP2)stars in galactic open clusters to shed more light on their origin andevolution. Aims: To study the group of CP2 stars, it is essential tofind these objects in different galactic environments and at a widerange of evolutionary stages. The knowledge of open cluster ages andmetallicities can help for finding a correlation between theseparameters and the (non-)presence of peculiarities, which has to betaken into account in stellar evolution models. Methods: Theintermediate band Δ a photometric system samples the depth of the5200 Å flux depression by comparing the flux at the centre withthe adjacent regions with bandwidths of 110 Å to 230 Å. Itis capable of detecting magnetic CP2 and CP4 stars with high efficiency,but also the groups of (metal-weak) λ Bootis and classicalBe/shell stars can be successfully investigated. In addition, it allowsthe age, reddening, and distance modulus to be determined withappropriate accuracy by fitting isochrones. Results: From the 1677observed members of the eight open clusters, one Ae and twenty-five CP2stars were identified. Furthermore nineteen deviating stars aredesignated as questionable for several reasons. The estimated age,reddening, and distance for the programme clusters were compared withpublished values of the literature and discussed in this context. Conclusions: .The current paper shows that CP2 stars are continuouslypresent in very young (7 Myr) to intermediate age (500 Myr) openclusters at distances greater than 2 kpc from the Sun.Based on observations at CASLEO, CTIO (Proposal 2003A-0057), and OSN.The Observatorio de Sierra Nevada is operated by the Consejo Superior deInvestigaciones Científicas through the Instituto deAstrofísica de Andalucía (Granada, Spain). Photometricdata are only avaialable in electronic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/462/591 Full Fig. [seefull textsee full textsee full textsee full textsee full text], Tables[see full textsee full textsee full textsee full textsee full text] and[see full textsee full textsee full textsee full textsee full text] areonly available in electronic form at http://www.aanda.org
| The Optical Gravitational Lensing Experiment. Variable Stars in the Field of Open Cluster NGC6259
We present the results of a search for variable stars in the field ofNGC6259. Altogether 85 variable stars have been discovered. 36 of themare eclipsing systems. This group contains 13 EA, 2 EB and 21 EW-typestars. Light curves of two variable stars resemble those of Miras. Theremaining 47 variable stars detected in the field of this open clusterare most probably highly obscured red giants (OSARG, irregular). For alldetected variable stars we provide their light curves, preliminaryclassification, discussion on the possible cluster membership,equatorial coordinates, finding charts and periods when possible.
| Deepsky delights.
Not Available
| Ages and metallicities of star clusters: New calibrations and diagnostic diagrams from visible integrated spectra
We present homogeneous scales of ages and metallicities for starclusters from very young objects, through intermediate-age ones up tothe oldest known clusters. All the selected clusters have integratedspectra in the visible range, as well as reliable determinations oftheir ages and metallicities. From these spectra equivalent widths (EWs)of K Ca II, G band (CH) and Mg I metallic, and Hδ, Hγ andHβ Balmer lines have been measured homogeneously. The analysis ofthese EWs shows that the EW sums of the metallic and Balmer H lines,separately, are good indicators of cluster age for objects younger than10 Gyr, and that the former is also sensitive to cluster metallicity forages greater than 10 Gyr. We propose an iterative procedure forestimating cluster ages by employing two new diagnostic diagrams and agecalibrations based on the above EW sums. For clusters older than 10 Gyr,we also provide a calibration to derive their overall metal contents.
| The relatively young, metal-poor and distant open cluster NGC 2324
We have obtained CCD photometry in the Johnson V, Kron-Cousins I andCT1 Washington systems for NGC 2324, a rich open clusterlocated 35° from the Galactic anticentre direction. We measuredV magnitudes and V-I colours for 2865 stars and T1 magnitudesand C-T1 colours for 1815 stars in an area of 13.6 arcmin× 13.6 arcmin. The comparison of the cluster colour-magnitudediagrams with isochrones of the Geneva group yield E(V-I) = 0.33± 0.07 and V-MV = 13.70 ± 0.15 for log t = 8.65(t = 440 Myr) and Z = 0.008 ([Fe/H] = -0.40), and E(C-T1) =0.40 ± 0.10 and T1-MT1 = 13.65 ±0.15 for the same age and metallicity level. The resulting E(V-I)reddening value implies E(B-V) = 0.25 ± 0.05 and a distance fromthe Sun of (3.8 ± 0.5) kpc. Star counts carried out within andoutside the cluster region allowed us to estimate the cluster angularradius as 5.3 arcmin ± 0.3 arcmin (5.9 pc). When using the E(B-V)reddening value here derived and the original Washington photometricdata of \citet{gcm91} for the stars confirmed as red cluster giants fromCoravel radial velocities, we found [Fe/H] = -0.31 ± 0.04, whichis in good agreement with the best fits of isochrones. Therefore, NGC2324 is found to be a relatively young, metal-poor and distant opencluster located beyond the Perseus spiral arm. A comparison of NGC 2324with 10 well-known open clusters of nearly the same age shows that thecluster metal abundance and its position in the Galaxy are consistentwith the existence of a radial abundance gradient of -0.07 dexkpc-1 in the Galactic disc.
| Integrated spectral evolution of Galactic open clusters
We present a library of 47 open-cluster integrated spectra, mostlyobtained at CASLEO (San Juan, Argentina) in the range 3600 < λ< 7400 Å, which are made available at CDS. The data arecombined with previous spectra to obtain 10 high signal-to-noise ratiobasic templates in the young and intermediate-age domains, which arealso provided in the library. These Galactic disc templates representthe increased time resolution spectral evolution of a stellar populationunit around the Solar metallicity level. The improved signal-to-noiseratio of the present templates with respect to previous template lists,together with their increased time resolution, allowed us to improve thefundamental parameters of some open clusters. The present spectrallibrary will be useful for several astrophysical applications,particularly for population syntheses of star-forming giant galaxies.
| Integrated photometric characteristics of galactic open star clusters
Integrated UBVRI photometric parameters of 140 galactic open clustershave been computed. Integrated I(V-R)0 and I(V-I)0colours as well as integrated parameters for 71 star clusters have beenobtained for the first time. These, in combination with published data,altogether 352 objects, are used to study the integrated photometriccharacteristics of the galactic open clusters. The I(MV)values range from -9.0 to -1.0 mag corresponding to a range in totalmass of the star clusters from ~ 25 to 4*E4 Msun.The integrated colours have a relatively narrow range, e.g., I(B-V){_0}varies from -0.4 to 1.2 mag. The scatter in integrated colours at agiven integrated magnitude can be understood in terms of differences infraction of red giants/supergiants in the clusters. The observedintegrated magnitudes and colours agree with the synthetic ones, exceptthe dependences of I(V-R)0 and I(V-I)0 colours forclusters younger than ~ 100 Myrs and also of the integrated magnitudesof oldest clusters. The large sample provides the most accurate agedependence of integrated magnitudes and colours determined so far. Theluminosity function of the I(MV) has a peak around -3.5 magand its slope indicates that only ~ 1% of the open clusters in thegalactic disc are brighter than I(MV)=-11 mag. No variationhas been found of integrated magnitude with galactocentric distance andmetallicity.
| Variable Stars in the Field of Young Open Cluster NGC 581
We present results of the search for variable stars in the field ofyoung open cluster NGC 581. Based on 19 nights of observations, 6 newvariable stars were discovered. Two of them turned out to be eclipsingbinary systems. Another two detected variable stars are most probably ofgamma Dor type. During our observations one of the known Be starslocated in our field of view showed irregular variations of brightness,typical for this class of stars. The sixth variable star is a pulsatingred giant.
| Modified Newtonian Dynamics as an Alternative to Dark Matter
Modified Newtonian dynamics (MOND) is an empirically motivatedmodification of Newtonian gravity or inertia suggested by Milgrom as analternative to cosmic dark matter. The basic idea is that ataccelerations below ao ~ 10-8 cm/s2 ~cHo/6 the effective gravitational attraction approaches√(gnao), where gn is the usualNewtonian acceleration. This simple algorithm yields flat rotationcurves for spiral galaxies and a mass-rotation velocity relation of theform M ∝ V4 that forms the basis for the observedluminosity-rotation velocity relation-the Tully-Fisher law. We reviewthe phenomenological success of MOND on scales ranging from dwarfspheroidal galaxies to superclusters and demonstrate that the evidencefor dark matter can be equally well interpreted as evidence for MOND. Wediscuss the possible physical basis for an acceleration-basedmodification of Newtonian dynamics as well as the extention of MOND tocosmology and structure formation.
| Variable Stars in the Field of Young Open Cluster NGC 659
We present results of the search for variable stars in young opencluster NGC 659. Based on 35 nights of observations, 7 new variablestars were discovered. Three of them are Be stars. Another three aremost probably pulsating variables of gamma Dor type. One star is adetached binary system.
| delta Scuti and related stars: Analysis of the R00 Catalogue
We present a comprehensive analysis of the properties of the pulsatingdelta Scuti and related variables based mainly on the content of therecently published catalogue by Rodríguez et al.(\cite{retal00a}, hereafter R00). In particular, the primaryobservational properties such as visual amplitude, period and visualmagnitude and the contributions from the Hipparcos, OGLE and MACHOlong-term monitoring projects are examined. The membership of thesevariables in open clusters and multiple systems is also analyzed, withspecial attention given to the delta Scuti pulsators situated ineclipsing binary systems. The location of the delta Scuti variables inthe H-R diagram is discussed on the basis of HIPPARCOS parallaxes anduvbybeta photometry. New borders of the classical instability arepresented. In particular, the properties of the delta Scuti pulsatorswith nonsolar surface abundances (SX Phe, lambda Boo, rho Pup, delta Deland classical Am stars subgroups) are examined. The Hipparcos parallaxesshow that the available photometric uvbybeta absolute magnitudecalibrations by Crawford can be applied correctly to delta Scutivariables rotating faster than v sin i ~ 100 km s{-1} withnormal spectra. It is shown that systematic deviations exist for thephotometrically determined absolute magnitudes, which correlate with vsin i and delta m1. The photometric calibrations are found tofit the lambda Boo stars, but should not be used for the group ofevolved metallic-line A stars. The related gamma Dor variables and thepre-main-sequence delta Scuti variables are also discussed. Finally, thevariables catalogued with periods longer than 0fd 25 are examined on astar-by-star basis in order to assign them to the proper delta Scuti, RRLyrae or gamma Dor class. A search for massive, long-period delta Scutistars similar to the triple-mode variable AC And is also carried out.
| Fundamental parameters of the moderately young open clusters NGC 5999, NGC 6031, Ruprecht 115 and Ruprecht 120
We present CCD BVI Johnson-Cousins photometry for the southern openclusters NGC 5999, NGC 6031, Ruprecht 115 and Ruprecht 120. The sampleconsists of about 1160 stars reaching down to V ~ 19 mag. From theanalysis of the colour-magnitude diagrams, we confirm the reality of theclusters and derive their fundamental parameters (reddening, distanceand age). We also present integrated spectra for NGC 6031, Ruprecht 115and Ruprecht 120, covering a range from 3500 to 9200 A. From theequivalent widths of Balmer and infrared Ca ii triplet lines, as well asfrom a comparison of the obtained spectra with those of templateclusters, we derive reddening, age and metallicity. The photometric andspectroscopic results allow us to conclude that the four clusters aremoderately young (age &sim 100-500 Myr) and are locatedapproximately towards the Galactic Centre at ~ 2.3 kpc from the Sun. NGC6031 and Ruprecht 120 have nearly solar metal content, while Ruprecht115 appears to be slightly metal-rich.
| The Optical Gravitational Lensing Experiment. A CCD Search for Variable Stars in Open Clusters - NGC5999
We report discovery of 41 variable stars in the field of the young opencluster NGC 5999. 30 stars have light curves typical for eclipsingsystems: this group contains three Algol-type and 27 WUMa type variablestars. One RR Lyr and one delta Scuti stars form a group of pulsatingvariables. Nine variable stars are of unknown type and classified asmiscellaneous. One of them is a periodic, most probablychromospherically active star. Our data are too scarce to make anyconclusion about periodicity of remaining eight variable stars.
| Optical Gravitational Lensing Experiment. A CCD Search for Variable Stars in Open Clusters -- NGC 5381
We present results of the search for variable stars in the field of theopen cluster NGC 5381. Observations conducted from March to September1997 led to discovery of 18 new variable stars. 13 stars are eclipsingvariables; light curves of 7 of them are typical for W UMa type starsand remaining six are EA Algol-like systems. Five stars, for which wecannot estimate periods from the present data, we call tentatively longterm variables. For previously known variable QR Cen an accurate lightcurve was obtained. This star turned out to be an EA type eclipsingsystem with the period of 2.^d2903 (about two times longer than obtainedearlier).
| Reddening and age for 11 Galactic open clusters from integrated spectra
We study integrated spectra of 11 Galactic open clusters in the visibleand near-infrared. We use continuum distribution and line strengths toinfer reddening, age and, in some cases, metallicity. These parametersare derived by using different methods, mainly by employing templateintegrated spectra of Magellanic Clouds and Galactic star clusters withknown properties, as well as a grid relating the equivalent widths ofspectral absorption lines to age and metallicity spanning a wide rangeof values. The results indicate a good agreement with previous workbased mainly on color-magnitude diagrams, when available. Internalreddening is significant for very young clusters like NGC 3603 and 6611.A Wolf-Rayet star in NGC 6231 is also analyzed spectroscopically in thecluster context. Wolf-Rayet features appearing in the integrated spectraof NGC 6231 and 3603 are employed as indicators of the clusterevolutionary stage. The oldest cluster in the sample has an age of about300 Myr. The present sample considerably improves the age resolutionaround solar metallicity in the cluster spectral library for populationsynthesis.
| Uniform survey of clusters in the southern Milky Way.
Abstract image available at:http://adsabs.harvard.edu/abs/1975AJ.....80...11V
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
Kataloglar ve belirtme:
|
