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V1154 Tau: a New Eclipsing Star within a Triple System
V1154 Tau has been discovered by Hipparcos as a a low amplitude variableof unsolved nature. We have carried out extensive B,V photometry fromDec 2002 to February 2003 and discovered that V1154 Tau is an eclipsingsystem with an orbital period of 1.7678805 days. The system is triplewith the third component on an extremely wide orbit, 0.355 arcsec away,or 90 AU at the system distance, contributing 21 of the total systemlight. The orbit of the eclipsing binary is eccentric and the totalcolor difference between primary and secondary eclipse is 0.02 mag inB-V, both being total with flat bottom.
| Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| 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.
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