N-body model of open cluster remnant NGC 1901

Milky Way galaxy hosts more than 2000 open clusters. Some of them are evolved clusters that dissolved by Galactic tidal field, leave behind only few members and known as Open Cluster Remnants (OCR). They have very low surface density but high binary fraction. One of well-studied OCRs is NGC 1901 (α = 5h18m15s and δ = −68°26’12”; l = 279.022° and b = −33.603°). This middle aged (approximately 400 to 850 Myr) cluster is 400 pc away from sun at the same direction of Large Magellanic Cloud. Based on astrometric, photometric, and spectroscopic observation, there are 13 cluster members confirmed with binary fraction of 62%, mostly A-F stars. According to several data and parameters derived from the observation of NGC 1901, the authors performed some N-body models using various initial mass function (IMF), density parameter, number of member, and primordial binary fraction. Evolution of these model were simulated under Galactic tidal field until completely dissolved. Model B84-600 with 600 members (single and binary), Kroupa IMF, density parameter W0 = 4, along with 40% primordial binary fraction gives fairly good result. At cluster age t ~ 800 Myr, this model leaves only 7% of its initial members with 50% binary fraction. Cluster’s structure which is parameterized by core radius (rc) 1.9 pc and tidal radius (rt) 5.6 pc rather close to observational study, rt = 6.2 pc. However, with density parameter log(rt/rc) = 0.45, this model is more loose compared to another observational analysis which yields log(rt/rc) = 0.64.