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CCD Photometry and Classification of Stars in the North America and Pelican Nebulae Region. III. The Dark Cloud L935
Magnitudes and color indices of 430 stars down to V ˜ 17.5 mag inthe eight-color Vilnius + I photometric system were obtained in fourareas of diameter 20' within the dark cloud L935 separating the NorthAmerica and Pelican nebulae. Spectral types, interstellar colorexcesses, extinctions and distances of stars were determined from thephotometric data. The plot of extinction vs. distance shows that thedark cloud begins at a distance of 520±50 pc. About 40 stars inthe cloud, mostly K and M dwarfs, are suspected to have Hαemission; these stars also exhibit infrared excesses. Four of them areknown pre-main-sequence stars. Our star set contains J205551.3+435225 (V= 13.24) which, according to Camerón and Pasquali (2005), is theO5 V type star ionizing the North America and Pelican nebulae. If thisspectral type is confirmed, the star would have an extinctionAV between 9 and 10 magnitudes (depending on the acceptedextinction law) and a distance which is not very different from the dustcloud distance.
| CCD Photometry and Classification of Stars in the North America and Pelican Nebulae Region. II. The Region of NGC 6996
Magnitudes and color indices of 620 stars down to V = 17.5 mag in theeight-color Vilnius + I photometric system are obtained in the area ofthe open cluster NGC 6996 in the North America Nebula. By combining theresults of optical photometry and the infrared 2MASS data an increasedvalue of the ratio of total-to-selective extinction is found. Forearly-type stars it corresponds to RBV=3.5. Spectral types,interstellar color excesses, extinctions and distances of stars aredetermined from the photometric data. The plot of extinction vs.distance shows that the extinction exhibits a steep rise at 400 pcreaching 3--4 mag. Forty seven main-sequence stars and three red giantsare identified as probable cluster members. The cluster distance isfound to be 794 pc by ZAMS fitting and 781 pc by averaging individualdistances of the 50 probable cluster members. The cluster stars show arange of interstellar extinction, with an average value of AVis 1.92 mag. Fitting the main sequence and red giants of the cluster tothe isochrones in the MV vs. (B--V)0 plane givesan age of 3.5× 108 yr. Probably NGC 6996 has no geneticrelation to the star-forming region in the North America and Pelicannebulae. About 35 stars in the magnitude range 16--17 in the field ofNGC 6996 are suspected to be O--B5 stars belonging to the Perseus spiralarm.
| Optical photometry and spectral classification in the field of the open cluster NGC 6996 in the North America Nebula
We present and discuss broad band CCD UBV(I)_C photometry and lowresolution spectroscopy for stars in the region of the open cluster NGC6996, located in the North America Nebula. The new data allow us totightly constrain the basic properties of this object. We revise thecluster size, which in the past has been significantly underestimated.The width of the Main Sequence is mainly interpreted in terms ofdifferential reddening, and indeed the stars' color excessEB-V ranges from 0.43 to 0.65, implying the presence of asignificant and evenly distributed dust component. We cross-correlateour optical photometry with near infrared photometry from 2MASS, and bymeans of spectral classification we are able to build extinction curvesfor an handful of bright members. We find that the reddening slope andthe total to selective absorption ratio R_V toward NGC 6996 areanomalous. Moreover the reddening-corrected colors and magnitudes allowus to derive estimates for the cluster distance and age, which turn outto be 760 ± 70 pc (V0-MV = 9.4 ±0.2) and 350 Myr, respectively. Based on our results, we suggestthat NGC 6996 is located in front of the North America Nebula, and doesnot seem to have any apparent relationship with it.Based on observations carried out at Asiago and Teramo Observatories,Italy.Photometry is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/419/149
| Proper motions of open clusters within 1 kpc based on the TYCHO2 Catalogue
We present mean absolute proper motions of 112 open clusters, determinedusing the data from the Tycho2 Catalogue. For 28 clusters, this is thefirst determination of proper motion. The measurements made use of alarge number of stars (usually several tens) for each cluster. The totalnumber of stars studied in the fields of the 164 open clusters is 5016,of which 4006 were considered members. The mean proper motions of theclusters and membership probability of individual stars were obtainedfrom the proper motion data by applying the statistical method proposedby Sanders (\cite{Sanders71}). Based on observations of the ESAHipparcos satellite. Tables 1, 2 and 5 to 117 are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/376/441
| Probable binary open star clusters in the Galaxy.
The existence of double/binary clusters in the Magellanic Clouds isfairly well established, whereas only one such pair, h + χ Persei,is known in the Galaxy. From the catalogues of open clusters of theGalaxy, we have identified 18 probable pairs of clusters (with knowndistances), with spatial separations less than 20pc. The tidaldisruption timescales for these pairs, due to Galactic differentialrotation are calculated, using cluster data where available or byassuming typical values. In some cases, these timescales are larger thanthe average open cluster lifetime, =~10^8^yr. About 8% of open clustersappear to be members of binary systems, and hence binary cluster systemsmay not be very uncommon in the Galaxy.
| Photometry of the open cluster NGC 6996 in the North America nebula
Thirty stars in the direction of the open cluster NGC 6996 are measuredin the Vilnius photometric system. Photometric spectral types, absolutemagnitudes, interstellar reddenings, extinctions, and distances aredetermined for most of them. Fifteen stars are suspected to be clustermembers. Their mean distance is 620 + or - 30 pc and mean extinctionA(v) is 1.74 mag. The extinction within the cluster is variable. The ageof the cluster is of the order of 100 million yr, and this excludes thepossibility that it is evolutionary related with the North America andPelican Nebulae complex. The distance of this complex 550 pc isconfirmed.
| Catalog of open clusters and associated interstellar matter.
Not Available
| Deep-sky wonders.
Not Available
| Clusters in the Region of the North America Nebula.
Not Available
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