The young open cluster NGc 1981

BRAZ ET AL.; A:E. PIATTI

BOLETIM DA SOCIEDADE ASTRONOMICA BRASILEIRA

SAB

Año: 2024

0101-3440

An stellar cluster is a gravitationally bound group of stars that present a common origin, so that its members have similar age, kinematics and chemical composition. The study of young clusters help to constrain the formation and evolution models as well as the Galatic disc properties. Open clusters in the embedded phase form at a rate that exceeds by more than an order of magnitude the forming rate of optically visible clusters, indicating that these young systems have a very low chance of survival. NGC 1981 is a young cluster, located 1◦ north of the Orion Nebula in the Galactic coordinates (l,b) = (208.9, -18.98). Although NGC 1981 is in a region of intense star formation, with several clouds of gas and dust, it presently inhabits a relatively dust-free field, perhaps as a consequence of its own evolution. Aiming to better understand the star formation in Orion, we have studied NGC 1981, which has been classified with two conflicting ages (30 and 5 Myrs). GAIA DR2 and EDR3 photometry and astrometry, medium resolution spectroscopy collected at CASLEO and OPD, have been analysed with our astrometric decontamination method and together with the radial velocity of the cluster members to dertermine, with better precision, the astrophysical parameters of NGC1981 and its neighbour cluster NGC 1977, which is contaminating spatially and astrometrically NGC 1981. Our analysis has revealed that NGC 1981 and NGC 1977 are indeed young, 8 Myrs and 4 Myrs old, respectively. These findings reinforce the scenario of sequential star formation in the Orion Nebula. The dispersion in the astrometric data of its members, suggest that NGC 1981 may be going through some disruptive processes and it is not expected to survive by more than a few million years.