The orbits of open clusters in the Galaxy

Abstract

We present and analyze kinematics and orbits for a sample of 488 open clusters in the Galaxy. The velocity ellipsoid for our present sample is derived as ($\sigma_{U}$, $\sigma_{V}$, $\sigma_{W})$=$(28.7$, 15.8, 11.0) km s$^{-1}$ which represents a young thin disc population. We also confirm that the velocity dispersions increase with the age of cluster subsample. The orbits of open clusters are calculated with three Galactic gravitational potential models. The errors of orbital parameters are also calculated considering the intrinsic variation of the orbital parameters and the effects of observational uncertainties. The observational uncertainties dominate the errors of derived orbital parameters. The vertical motions of clusters calculated using different Galactic disc models are rather different. The observed radial metallicity gradient of clusters is derived with a slope of $b=-0.070\pm0.011$ dex kpc$^{-1}$. The radial metallicity gradient of clusters based on their apogalactic distances is also derived with a slope of $b=-0.082\pm0.014$ dex kpc$^{-1}$. The distribution of derived orbital eccentricities for open clusters is very similar to the one derived for the field population of dwarfs and giants in the thin disc.Comment: Accepted for Publication in MNRAS, 25 pages, 14 figures, 6 table

Proper motions of young stars in Chamaeleon

“…The mean UCAC3 proper motions for these two groups are in good agreement with previously published values (Kharchenko et al 2005;Wu et al 2009). Interestingly, the total proper motion is very similar in both associations, as shown by the histograms in Fig.…”

“…Table 6 also lists the arithmetic and weighted mean radial velocities that we derive for three of the four groups. For the and η Cha clusters, the mean radial velocities are in good agreement with previously published values (Kharchenko et al 2005;Wu et al 2009). …”

The evolution of the Milky Way: new insights from open clusters

“…In contrast, blurring conserves the angular momentum of individual stars but heats the disc in the radial direction, thereby configuring the orbit to eccentric over time so that a star can cover a wider range in galactocentric radii. As a result, all the previously used static and axisymmetric Galactic potential models of Fellhauer et al (2006), Allen &Santillan (1991) andFSC96, andBovy et al (2015) in the orbit reconstruction of OCs by Vande Putte et al (2010), Wu et al (2009), andCantat-Gaudin et al (2016), respectively, and the one adopted in this study yield spurious birthplaces if the radial mixing happened by churning. Therefore, this process is successful in recovering the genuine orbital history and birthplace of OCs only if they underwent radial mixing originating from blurring process.…”

“…We have adopted the static, axisymmetric Galactic gravitational potential model of Flynn, Sommer-Larsen & Christensen (1996, hereafter FSC96) representing a spherical central bulge composed of a superposition of two Plummer spheres (Plummer 1911), a disc potential made up of three concentric analytical discs of Miyamoto-Nagai (1975), and a massive dark halo modeled as a spherical logarithmic potential. For this potential, we adopt a distance of the Sun to Galactic centre of 8 kpc with a local circular velocity of 220 km s −1 (same as adopted earlier in Wu et al 2009). …”

“…The cooler main sequence stars or red giants which are members of OCs provide not only abundance estimates for elements sampling all the major processes of stellar nucleosynthesis -but a collection of stars whose age, distance, kinematics and metallicity can be measured with greater certainty than for field stars. Moreover, it is possible from an OC's space motion and a model of the Galactic gravitational potential to study the dynamics and estimate a cluster's birthplace (Wu et al 2009;Vande Putte et al 2010).…”