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Overlapping Open Clusters NGC 1750 and NGC 1758 Behind the Taurus Dark Clouds. II. CCD Photometry in the Vilnius System
Seven-color photometry in the Vilnius system has been obtained for 420stars down to V = 16 mag in the area containing the overlapping openclusters NGC 1750 and NGC 1758 in Taurus. Spectral and luminosityclasses, color excesses, interstellar extinctions and distances aregiven for 287 stars. The classification of stars is based on theirreddening-free Q-parameters. 18 stars observed photoelectrically wereused as standards. The extinction vs. distance diagram exhibits thepresence of one dust cloud at a distance of 175 pc which almostcoincides with a distance of other dust clouds in the Taurus complex.The clusters NGC 1750 and NGC 1758 are found to be at the same distanceof ~ 760 pc and may penetrate each other. Their interstellarextinction A_V is 1.06 mag which corresponds to EB-V = 0.34mag.
| The overlapping open clusters NGC 1750 and NGC 1758. II. $\vec BVR photographic photometry and proper motions
Astrometry (positions and proper motions) and photographic BVRphotometry were determined from a set of 29 photographic plates and CCDdata in a region of 2.3(deg}x2.3({deg)) in the area of open clusters NGC1750 and NGC 1758 in Taurus. The iterative central overlap algorithm wasused for the proper motion calculations. Plate-to-plate transformationsand astrometric magnitude effects are discussed in detail. CCD datainteract with photographic material in three different ways: for theelimination of astrometric magnitude effects, for the photometricstandard calibration of photographic plates and for building a CCDpseudo-plate used for astrometric purposes as any other photographicplate. A preliminary analysis of the resulting photometric andastrometric catalogue confirmed the reality of two different clusters inthe zone (NGC 1750 and NGC 1758). There were no indications for theexistence of NGC 1746. Tables 6 and 11 are only available in electronicform from CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/Abstract.html
| Determination of proper motions and membership of the open clusters NGC 1750 and NGC 1758
The kinematic state of the open clusters NGC 1750 and NGC 1758 has beenstudied using newly determined proper motions for 540 stars in a fieldof 1.5 deg x 1.5 deg in the Taurus dark cloud region. The proper motionsare obtained from the reduction of PDS measurements of 20 plates thatspan a total time interval of 68 years, resulting in an average propermotion accuracy of 0.67 mas/yr. These proper motions are used todetermine the membership probabilities of stars in the region by meansof a new, improved method described in this paper. Of the 540 starsanalyzed here, 332 are found to be probable members of NGC 1750, and 23are probable members of NGC 1758. The core radii of NGC 1750 and NGC1758 are determined to be 17'2 and 2'25 respectively.
| The overlapping open clusters NGC 1750 and NGC 1758. I. UBVRI-CCD photometry
The existence and relationship of the possible clusters NGC 1746, NGC1750 and NGC 1758 has been a matter of discussion during the lastdecades. This star field is close to the galactic anticenter and lies inthe direction of the Taurus dark cloud complex. As part of acomprehensive astrometric and photometric analysis of this zone, wepresent a brief historical introduction together with deep UBVRI-CCDphotometry of the area. The presence of at least one cluster can bededuced from these data. This object has a position and apparent sizecompatible with those previously quoted for NGC 1750 and NGC 1758. It isnot possible to distinguish the single or double nature of the clusteron the sole basis of our photometry and the spatial distribution of thestars. No photometric evidence was found for NGC 1746. Based onobservations made at the Centro Astronómico Hispano-Alemánand the Observatorio Astronómico Nacional in Calar Alto, Almeria,Spain. Table 5 is only available in electronic form from CDS viaanonymous ftp 130.79.128.5, and by e-mail request todgaladi@pchpc5.am.ub.es
| The Henry Draper Extension Charts: A catalogue of accurate positions, proper motions, magnitudes and spectral types of 86933 stars
The Henry Draper Extension Charts (HDEC), published in the form offinding charts, provide spectral classification for some 87000 starsmostly between 10th and 11th magnitude. This data, being highlyvaluable, as yet was practically unusable for modern computer-basedastronomy. An earlier pilot project (Roeser et al. 1991) demonstrated apossibility to convert this into a star catalogue, using measurements ofcartesian coordinates of stars on the charts and positions of theAstrographic Catalogue (AC) for subsequent identification. We presenthere a final HDEC catalogue comprising accurate positions, propermotions, magnitudes and spectral classes for 86933 stars of the HenryDraper Extension Charts.
| Probable open clusters NGC 1750 and NGC 1758 behind the Taurus dark clouds
The area of 2.5 x 2.5 deg in the direction of the Taurus dark cloudscontaining stellar groupings NGC 1746, NGC 1750, and NGC 1758 isinvestigated in the Vilnius photometric system. Magnitudes V, colorindices, color excesses, interstellar extinctions, and distances aredetermined for 116 stars, some of which are as faint as V = 13. It isconcluded that NGC 1746 is probably not a cluster. Other two groupingsof stars, NGC 1750 and NGC 1758, if real, may be open clusters at 510and 680 pc distances. Interstellar reddenings E(B-V) of both groups are0.42 and 0.37 mag, respectively. The distance of the Taurus dark cloudsin the area is found to be 175 pc, i.e. by 45 pc larger than in otherdirections farther to the south from the galactic equator.
| Red indices in galactic clusters
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