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Open clusters or their remnants: B and V photometry of NGC 1901 and NGC 1252
Photometry in the B and V bands is presented for the southern stellargroups NGC 1901 and NGC 1252. NGC 1901 is often described as an opencluster while NGC 1252 consists of a concentration of about 20 starscentered ~20' north of the original New General Cataloguecoordinates, and at the southwest edge of the large region previouslyassigned to this object in the literature. NGC 1901 has a clear mainsequence and shares similarities with the Hyades. We derive a reddeningvalue E(B-V) = 0.04, a distance from the Sun dsun = 0.45 kpc(Z = -0.23 kpc) and an age 0.6 +/- 0.1 Gyr. NGC 1901 is conclusively aphysical system, dynamically comparable to or more evolved than theHyades. The colour-magnitude diagram of NGC 1252 suggests a turnoff andmain sequence, and a total of 12 probable members. We simulated theGalactic field colour-magnitude diagram in the same direction and foundit to be a poor match to NGC 1252, suggesting that NGC 1252 is not afield fluctuation. Isochrone fitting to the probable members isconsistent with E(B-V) = 0.02, dsun = 0.64 kpc (Z = -0.46kpc) and an age 3 +/- 1 Gyr. NGC 1252 cannot be ruled out as a physicalgroup with the available data. If so, evidence is found that it is not aclassical open cluster, but rather an open cluster remnant.
| CCD photometry and astrometry of visual double and multiple stars of the HIPPARCOS Catalogue. II. CCD photometry and differential astrometry of 288 southern ``Intermediate'' systems
We present photometric and astrometric data of about 280 visual doublestars of the ``intermediate'' class, i.e. with angular separationsmainly in the range 2arcsec < rho < 12arcsec . The observationshave been obtained in 1991-92 with a CCD camera attached to the 91 cmDutch telescope at ESO La Silla, Chile. Differential magnitudes of thedouble star components as well as magnitudes and colour indices of theindividual components have been determined in the Cousins V and Ipassbands with an internal error of about 0.005 mag and an externalaccuracy of less than 0.03 mag. In addition, angular separations havebeen secured to an internal accuracy of 0.004arcsec and position anglesto about 0.05degr. Tables 1 to 4 are only available in electronic format the CDS via ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html. Based on observationscollected at the European Southern Observatory, La Silla, Chile.
| TW Horologii and NGC 1252 - A rebuttal
The Bouchet and The(1983) suggestion that the carbon variable TW Hor isa member of the open cluster NGC 1252 is questioned on the basis of CapeZone Catalog data for the ten stars observed by them. The most probablemembership for the variable is presently held to be in the HyadesSupercluster, and a distance modulus of 7.7 mag is given. Bouchet andThe's derived distance of 500 parsecs would place NGC 1252 400 pc abovethe galactic plane, which is higher than might be expected for what theyregard as a young disk cluster.
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