Contingut
Imatges
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
CCD BVI photometry and Coravel observations of stars in the open cluster NGC2489
We present CCD BVI photometry for the southern open cluster NGC2489 andits surrounding field. The sample consists of 2182 stars measured in anarea of 13.6 × 13.6 arcmin2, extending down to V ~21.5. These data are supplemented with CORAVEL radial-velocityobservations for seven red giant candidates. A cluster angular radius of6.7 +/- 0.6 arcmin, equivalent to 3.5 +/- 0.3 pc, is estimated from starcounts carried out inside and outside the cluster region. The comparisonof the cluster colour-magnitude diagrams with isochrones of the Padovagroup yields E(B - V) = 0.30 +/- 0.05, E(V - I) = 0.40 +/- 0.05 and V -MV = 12.20 +/- 0.25 for log t = 8.70 (t =500+130-100 Myr) and Z = 0.019. NGC2489 is thenlocated at 1.8 +/- 0.3 kpc from the Sun and 25 pc below the Galacticplane. The analysis of the kinematical data allowed us to confirmcluster membership for six red giants, one of them being a spectroscopicbinary. A mean radial velocity of 38.13 +/- 0.33 km s-1 wasderived for the cluster red giants. The properties of a sample of openclusters aligned along the line of sight of NGC2489 are examined.
| Photometric and Coravel observations of red giant candidates in three open clusters: membership, binarity, reddening and metallicity
Aims.We present new CORAVEL radial-velocity observations andphotoelectric photometry in the UBV and DDO systems for a sample ofpotential members of the red-giant branches of NGC 6192, NGC 6208 andNGC 6268, three open clusters projected close to the Galactic centerdirection. We also examine the properties of a sample of 42 inner diskopen clusters projected towards almost the same direction as the threeclusters. Methods: .Cluster members and red field giants werediscriminated by using the CORAVEL radial-velocity data and by applyingtwo photometric criteria. Interstellar reddening and metal content ofthe clusters were derived from combined BV and DDO data. Results:.Cluster membership for five red giants in NGC 6192, three in NGC 6208and three in NGC 6268 has been confirmed by the analysis of thephotometric and kinematic data. Photometric membership probabilitiesshow very good agreement with those obtained from CORAVEL radialvelocities. Three new spectroscopic binaries were discovered among thered giants of NGC 6192 and NGC 6208. Mean radial velocities and E(B-V)colour excesses were derived. Conclusions: .The overallmetallicities were found to be nearly solar for NGC 6208 and above solarfor NGC 6192 and NGC 6268. Most of the clusters located closer than 2kpc from the Sun in the considered direction are slightly more reddenedthan the absorption resulting from the Baade's window absorption law.
| First estimates of the fundamental parameters of the relatively bright Galactic open cluster NGC 5288
In this paper we present charge-coupled device (CCD) images in theJohnson B and V and Kron-Cousins I passbands for the previouslyunstudied open cluster NGC 5288. The sample consists of 15688 starsreaching down to V~ 20.5. The cluster appears to have a relatively smallbut conspicuous nucleus and a low-density extended coronal region. Starcounts carried out in 25 × 25 pixel2 boxes distributedthroughout the whole observed field allowed us to estimate the angularcore and corona radii as ~1.3 and 6.3arcmin, respectively. Our analysissuggests that NGC 5288 is moderately young and probably more metal-richthan the Sun. Adopting the theoretical metal content Z= 0.040, whichprovides the best global fit, we derive an age of130+40-30Myr. Simultaneously, we have obtainedcolour excesses E(B-V) = 0.75 and E(V-I) = 0.95 and an apparent distancemodulus V-MV= 14.00. The law of interstellar extinction inthe cluster direction is found to be normal. NGC 5288 is located at 2.1+/- 0.3kpc from the Sun beyond the Carina spiral feature and ~7.4kpcfrom the Galactic Centre. The cluster metallicity seems to be compatiblewith the cluster position in the Galaxy, given the recognized radialabundance gradient in the disc. For the first time, in this paper wedetermine the basic parameters for the open cluster NGC 5381, situatedin the same direction as NGC 5288. This determination was reached byusing CCD VI data published almost a decade ago by Pietrzyński etal. (1997) for NGC 5381. The properties of some open clusters alignedalong the line of sight of NGC 5288 are examined. The properties ofclusters of similar ages to NGC 5288 are also looked into. Evidence ispresented that these did not form mainly along the spiral arms butrather in the thin Galactic disc (Z~+/-100pc).
| Proper motion determination of open clusters based on the UCAC2 catalogue
We present the kinematics of hundreds of open clusters, based on theUCAC2 Catalogue positions and proper motions. Membership probabilitieswere obtained for the stars in the cluster fields by applying astatistical method uses stellar proper motions. All open clusters withknown distance were investigated, and for 75 clusters this is the firstdetermination of the mean proper motion. The results, including the DSSimages of the cluster's fields with the kinematic members marked, areincorporated in the Open Clusters Catalogue supported on line by ourgroup.
| New fundamental parameters for the inner disk open cluster Lyngå 11
We have obtained CCD BVIKC photometry down to V ˜ 21.5for the open cluster Lyngå 11 and its surrounding field. Thispreviously unstudied object appears to be rich and highly absorbed. Acluster angular radius of 4.5′ ± 0.5′, equivalent to(3.0 ± 0.3) pc, is estimated from star counts in 100-pixel a sideboxes distributed throughout the whole observed field. Our analysissuggests that Lyngå 11 is moderately young and probably of solarmetallicity. Adopting the theoretical metal content Z = 0.02, whichprovides the best global fit, we derive an age of (630 ± 70) Myr.Simultaneously, colour excesses E(B ‑ V) = 0.70 and E(V ‑ I)= 0.85 and an apparent distance modulus V ‑ MV = 14.0are obtained. These results place Lyngå 11 at a distance of (2.3± 0.5) kpc from the Sun and ˜6.5 kpc from the Galacticcentre. The properties of a sample of clusters aligned along theline-of-sight of Lyngå 11 are examined as well.
| A CCD BVI Photometric Study of the Young, Highly Reddened Open Cluster NGC 6318
We present CCD BVI photometry for the southern open cluster NGC 6318.The sample consists of 9876 stars measured in an area of13.6m×13.6m, extending down to V~21.5 mag. Star countscarried out within and outside the cluster region allowed us to estimatethe cluster angular radius as ~8'. The comparison of the clustercolor-magnitude diagrams with isochrones of the Geneva group yieldsE(B-V)=1.20+/-0.05, E(V-I)=1.55+/-0.10, and V-MV=15.45+/-0.35for logt=8.20 (t=160 Myr) and Z=0.020. NGC 6318 is then located at2.1+/-0.5 kpc from the Sun and 30 pc below the Galactic plane. Using theWEBDA open cluster database, we examined the structure of the Galacticdisk along the line of sight of NGC 6318. Among the known clusters inthis direction, HM 1 and BH 222 are the farthest ones, while thoselocated between 1 and 2 kpc of the Sun appear to be more absorbed thanthose expected to follow a quasi-linear extinction law.
| 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.
| 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.
| Two highly reddened young open clusters located beyond the Sagittarius arm
We present the results of CCD BVI Johnson-Cousins photometry down to V ~19 mag in the regions of the unstudied stellar groups Pismis 23 and BH222, both projected close to the direction towards the Galactic centre.We measured V magnitude and B-V and V-I colours for a total of 928 starsin fields of about 4arcmin x4arcmin . Pismis 23 is conclusively aphysical system, since a clear main sequence and other meaningfulfeatures can be seen in the colour-magnitude diagrams. The reality ofthis cluster is also supported by star counts carried out within andoutside the cluster field. For Pismis 23 we derive colour excessesE(B-V) = 2.0 +/- 0.1 and E(V-I) = 2.6 +/- 0.1, a distance from the Sunof 2.6 +/- 0.6 kpc (Z = -19 pc) and an age of 300 +/- 100 Myr (assumingsolar metal content). BH 222 appears to be a young open cluster formedby a vertical main sequence and by a conspicuous group of luminous,typically red supergiant stars. We derived for this cluster a colourexcess of E(V-I) = 2.4 +/- 0.2, a distance from the Sun of 6.0 +/- 2.7kpc (Z = -46 pc) and an age of 60 +/- 30 Myr. The resulting reddeningand distance estimates place these two young objects among the mostreddened and distant open clusters known in the direction towards theGalactic centre. They are located beyond the Sagittarius arm, close tothe direction where this arm probably bifurcates into two arms. Based onobservations made at the University of Toronto (David DunlapObservatory) 24-inch telescope, Las Campanas, Chile. Tables \ref{t2} and3 are only available 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/388/179
| BVI photometry and integrated spectroscopy of the very young open clusters Ruprecht 119, NGC 6318 and BH 245
We present CCD BVI observations obtained for stars in the fields of theunstudied or poorly studied open clusters Ruprecht 119, NGC 6318, and BH245 projected close to the direction towards the Galactic centre. Wemeasured V magnitude and B-V and V-I colours for about 600 starsreaching down to V ~ 19 mag. From the analysis of the colour magnitudediagrams, we confirmed the physical reality of the clusters and derivedtheir reddening, distance and age for the first time. In addition, weobtained flux-calibrated integrated spectra in the range 3500-9200Å for the cluster sample. Using the equivalent widths of theBalmer lines and comparing the cluster spectra with template spectra wederive both foreground reddening and age. The photometric andspectroscopic results reveal that the three studied objects are veryyoung open clusters with ages ranging between 10 and 15 Myr, which havealready undergone the HII region evolutionary phase and are dominated bythe upper MS stars. The clusters, located between 1.1 kpc and 3.3 kpcfrom the Sun, are affected by different amounts of interstellar visualabsorption (2.4 <= A_v <= 7.0). In particular, BH 245 turned outto be a highly reddened open cluster located at a distance of scarcely1.1 kpc. Based on observations made at the University of Toronto (DavidDunlap Observatory) 24inch telescope, Las Campanas, Chile, and at theComplejo Astronómico El Leoncito, which is operated underagreement between the Consejo Nacional de InvestigacionesCientíficas y Técnics de la República Argentina andthe National Universities of La Plata, Córdoba, and San Juan,Argentina.
| Colour excesses and absolute magnitudes for non-Cepheid F-G supergiants from uvbybeta photometry
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990A&A...239..205A&db_key=AST
|
Enviar un nou article
Enllaços Relacionats
- - No s'ha trobat enllaços -
Enviar un nou enllaç
Membre dels grups següents:
|
Dades d'Observació i Astrometria
Catàlegs i designacions:
|
