NGC 2659: a probable binary cluster

Abstract

We present and discuss photometric data, proper motions and parallaxes in a field of a 30'x30' centred in the area centered in the open cluster NGC 2659 in the region of Vela. In recent papers on the same region evidences of the presence of another cluster close to the north-east of NGC 2659 have been reported. Data were extracted from Gaia EDR3 and have been employed in combination with ASteCA package to investigate the dimensional structure of the region occupied by this cluster. Surprisingly, by combining parallaxes and proper motions we identify two star groups superposed along the line of sight, and separated from each other by about 100 pc, instead of just one as suggested in the past and present literature. One of them, the younger one, has been historically identified as NGC 2659 while the other is a relatively old open cluster covering a larger area but placed in front of NGC 2659 and is identified as Pismis 9. After assessing individual group membership, we derive their kinematics (mean proper motion components), distances, ages and also the metal content.