The Structure and the Distance of Collinder 121 from Hipparcos and Photometry: Resolving the Discrepancy

Abstract

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 been already 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 uvbybeta parallaxes, but the structure of the field they reveal is no longer in discrepancy with that found by the photometric method.

arXiv comment7 pages, 1 figure, ApJL accepted

References in corpus (9)

• A Hipparcos census of the nearby OB associations
• The Problem of Hipparcos Distances to Open Clusters: I. Constraints from Multicolor Main Sequence Fitting
• Confirmation of Errors in Hipparcos Parallaxes from HST/FGS Astrometry of the Pleiades
• Correlated errors in Hipparcos parallaxes towards the Pleiades and the Hyades
• The problem of the Pleiades distance. Constraints from Stromgren photometry of nearby field stars
• The Problem of Hipparcos Distances to Open Clusters. II. Constraints from Nearby Field Stars
• WIYN Open Cluster Study. XXVI. Improved kinematic membership and spectroscopy of IC 2391
• The distance to the Pleiades: Main sequence fitting in the near infrared
• On the Nature of Collinder 121: Insights from the Low-Mass Pre-Main Sequence

Cited by in corpus (7)

• 3D maps of the local ISM from inversion of individual color excess measurements
• Identifying birth places of young isolated neutron stars
• Unlocking Galactic Wolf-Rayet stars with $\text{Gaia}$ DR2 II: Cluster and Association membership
• A revisit to agglomerates of early-type Hipparcos stars
• Galactic Structure Toward the Carina Tangent
• Massive Stellar Content of the Galactic Supershell GSH 305+01-24
• Stellar clustering and the kinematics of stars around Collinder 121 using Gaia DR3