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The structure and the distance of Collinder 121 from Hipparcos and photometry: resolving the discrepancy

Kaltcheva, Nadia and Makarov, Valeri V. (2007) The structure and the distance of Collinder 121 from Hipparcos and photometry: resolving the discrepancy. Astrophysical Journal, 667 (2). L155-L157. ISSN 0004-637X. doi:10.1086/522495.

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We present further arguments that the Hipparcos parallaxes for some of the clusters and associations represented in the Hipparcos catalog should be used with caution in the study of the Galactic structure. It has already been shown that the discrepancy between the Hipparcos and ground-based parallaxes for several clusters including the Pleiades, Coma Ber, and NGC 6231 can be resolved by recomputing the Hipparcos astrometric solutions with an improved algorithm diminishing correlated errors in the attitude parameters. Here we present new parallaxes obtained with this algorithm for another group of stars with discrepant data - the galactic cluster Cr 121. The original Hipparcos parallaxes led de Zeeuw et al. to conclude that Cr 121 and the surrounding association of OB stars form a relatively compact and coherent moving group at a distance of ≃550-600 pc. Our corrected parallaxes reveal a different spatial distribution of young stellar populace in this area. Both the cluster Cr 121 and the extended OB association are considerably more distant (750 - 1000 pc), and the latter has a large depth probably extending beyond 1 kpc. Therefore, not only are the recalculated parallaxes in complete agreement with the photometric uvbyβ parallaxes, but the structure of the field they reveal is no longer in discrepancy with that found by the photometric method.

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Additional Information:© 2007 The American Astronomical Society. Received 2007 June 15; accepted 2007 August 15; published 2007 September 19. We are grateful to the referee R. Hanson for a number of valuable comments. A UW Oshkosh Vander Putten Award is acknowledged. Partial support was provided by the National Science Foundation under grant AST-0708950 to N. K. The research described in this Letter was in part carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.
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Subject Keywords:galaxy: structure; open clusters and associations: individual (Collinder 121); stars: distances
Issue or Number:2
Record Number:CaltechAUTHORS:KALapjl07
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:13425
Deposited By: Tony Diaz
Deposited On:27 May 2009 21:38
Last Modified:08 Nov 2021 22:37

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