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The nature of some doubtful open clusters as revealed by HIPPARCOS
We discuss the nature of some galactic open clusters by using propermotions and parallaxes from the Hipparcos and ACT catalogues. We showthat the clusters Collinder 399, Upgren 1, NGC 1252 and Melotte 227 donot exist. Collinder 132 is found to be mainly composed out of membersof an OB association, but there may be a star cluster present in thisarea too. Roeser & Bastian (1994) proposed that NGC 2451 consists oftwo star clusters. We show that NGC 2451 A definitively does exist, NGC2451 B may exist. A star cluster may also be present in the area ofRoslund 5. The Hipparcos data finally confirm the reality of Collinder135.
| 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.
| Notes on the open cluster NGC 1252 with the variable carbon star TW Horologii as a probable member
Photometric observations of 38 objects in the vicinity of the opencluster NGC 1252 obtained in the UBVRI passbands using a 15.5-arcsecdiaphragm and an RCA 31034A photoelectric tube on the 50-cm and 1-mtelescopes at ESO in November, 1982, are reported. A visualidentification chart and color-color and color-magnitude diagrams areshown, and the photometric data are presented in a table. Fourteenobjects, including the N-type semiregular variable TW Hor (HD 20234),are found to belong to the cluster, which has approximate age = 5 x 10to the 8th years, distance = 470 pc, and diameter (for the 14 objects) =8 pc. The bolometric magnitude of TW Hor is estimated as -5.32 arcmin,suggesting that it belongs to the young population of the disk.
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | שעון |
| התרוממות ימנית: | 03h08m23.93s |
| סירוב: | -57°00'35.8" |
| גודל גלוי: | 8.97 |
| מרחק: | 523.56 פארסק |
| תנועה נכונה: | 17.1 |
| תנועה נכונה: | -12.3 |
| B-T magnitude: | 10.629 |
| V-T magnitude: | 9.107 |
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