Galactic Rotation Parameters from Data on Open Star Clusters.pdf

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Galactic Rotation Parameters from Data on Open Star Clusters.pdf

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Galactic Rotation Parameters from Data on Open Star Clusters

a r X i v : 0 7 0 9 .4 1 6 1 v 1 [ a s t r o - p h ] 2 6 S e p 2 0 0 7 ISSN 1063-7737, Astronomy Letters, 2007, Vol. 33, No. 11, pp. 720–728. c?Pleiades Publishing, Inc., 2007. Original Russian Text c?V.V. Bobylev, A.T. Bajkova, 2007, published in Pis’ma v Astronomicheski?? Zhurnal, 2007, Vol. 33, No. 11, pp. 809–818. Galactic Rotation Parameters from Data on Open Star Clusters V.V. Bobylev, A.T. Bajkova, and S.V. Lebedeva Central (Pulkovo) Astronomical Observatory of RAS, St-Petersburg Abstract–Currently available data on the field of velocities Vr, Vl, Vb for open star clusters are used to perform a kinematic analysis of various samples that differ by heliocentric distance, age, and membership in individual structures (the Orion, Carina–Sagittarius, and Perseus arms). Based on 375 clusters located within 5 kpc of the Sun with ages up to 1 Gyr, we have determined the Galactic rotation parameters ω0 = ?26.0±0.3 km s ?1 kpc?1, ω′0 = 4.18 ± 0.17 km s ?1 kpc?2, ω′′0 = ?0.45 ± 0.06 km s ?1 kpc?3, the system contraction parameter K = ?2.4 ± 0.1 km s?1 kpc?1, and the parameters of the kinematic center R0 = 7.4± 0.3 kpc and l0 = 0± 1 ?. The Galactocentric distance R0 in the model used has been found to depend significantly on the sample age. Thus, for example, it is 9.5 ± 0.7 kpc and 5.6 ± 0.3 kpc for the samples of young (≤ 50 Myr) and old ( 50 Myr) clusters, respectively. Our study of the kinematics of young open star clusters in various spiral arms has shown that the kinematic parameters are similar to the parameters obtained from the entire sample for the Carina-Sagittarius and Perseus arms and differ significantly from them for the Orion arm. The contraction effect is shown to be typical of star clusters with various ages. It is most pronounced for clusters with a mean age of ≈ 100 Myr, with the contraction velocity being Kr = ?4.3± 1.0 km s?1. INTRODUCTION The Galactic rotation parameters have been repeatedly determined by many authors using objects belonging