Abstract
The nature of the Local (Orion) arm - LOA is poorly known. We summarize the first results from a program to determine its properties, based on a large and homogeneous set of kinematic and photometric data. We present a study of the LOA cluster NGC 2302 (Costa et al. 2015, A&A, 580, A4) which includes a photometric analysis and determination of its kinematic properties and orbital parameters. A density analysis revealed a round concentration of stars within a radius of 2.5', centered at α2000=102.965916°, δ2000=-7.086300° Making a geometric registration of our first and second epoch frames (12-year timebase), we determined the systemic PM of NGC 2302 relative to the local field, and, through a comparison with UCAC4, we transformed this PM into absolute. We obtained: μα cosδ, μδ=(-2.09,-2.11) mas yr-1, with a standard error of 0.40 mas yr-1, per coordinate. Using medium-resolution spectroscopy of 76 stars in the field, we derived its systemic RV, which resulted to be 31.2 km sec-1, with a standard error of 0.7 km sec-1. With photometric diagrams we identified the stellar populations in the field. More than one exists, each affected by a different reddening, with the cluster sequence at E(B-V)=0.23. Isochrone fits, displaced for this reddening and for a distance modulus of (m-M)0=10.69 (d=1.40> kpc), indicate a cluster age of log(t)=7.90-8.00. With the kinematics and distance we determined the space motion of NGC 2302, by adopting a gravitational potential for the MW. The shape of the orbit and the resulting orbital parameters, indicate that it is a typical PopI object.
