2013A&A...553A.108C

An OB association is a gravitationally unbound group of stars. The identification of the members of the association is an important aspect of its study. There are few astrometric membership studies for OB associations, but the combination of these studies with astrophysical techniques becomes a very powerful tool for this type of research. We perform new spectroscopic and astrometric studies of the members of the association CentaurusOB1 (CenOB1) and the open cluster NGC4755. To carry out this study we used new spectroscopic optical observations obtained at CASLEO, and proper motion and photometric data from the Tycho-2 Catalogue and other databases available via the Internet. With this investigation we found 52 members of CenOB1 (l = 303.7,deg b = 0.4)deg and four members of NGC4755 (l = 303.2,deg b = 2.5),deg an open cluster integrated into the CenOB1 stellar association. The distance, heliocentric radial velocity, proper motion, and age of CenOB1 are 2.6 ±0.5 kpc, ~-20 km/s, µ_αcos δ = -4.78 ±0.10 mas/yr, µ_δ = -0.93 ±0.10 mas/yr, and ∼20x10⁶ years old, respectively. The same parameters found for NGC4755 are 1.9 ±0.5 kpc, -18 ±2 km/s, µ_αcos δ = -4.14 ±0.19 mas/yr, µ_δ = -1.09 ±0.12 mas/yr, and ∼15x10⁶ years old. The pulsars PSR J1253-5820 and PSR J1254-6150 could have been born as the result of supernovae explosions that occurred in the past by massive members of CenOB1. We have seen Infrared Astronomical Satellite (IRAS) sources near CenOB1, that show that star formation is still occurring. The age gradient observed between the different members of CenOB1 makes it likely that the stellar association and IRAS sources represent different stages of a sequential formation process.