Methods for improving open cluster fundamental parameters applied to M 52 and NGC 3960

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作者：
Bonatto, C. [1 ]
Bica, E. [1 ]
机构：
[1] Universidade Federal do Rio Grande do Sul, Instituto de Física, CP 15051, Porto Alegre 91501-970, RS, Brazil
来源：
Astronomy and Astrophysics | 1600年 / 455卷 / 03期
关键词：
Aims. We derive accurate parameters related to the CMD; structure and dynamical state of M 52 and NGC 3960; whose fields are affected by differential reddening. Previous works estimated their ages in the ranges 35-135 Myr and 0.5-1.0 Gyr; respectively; Methods; J; H and Ks 2MASS photometry with errors core = 0.91 ± 0.14 pc and Rlim = 8.0 ± 1.0 pc. NGC 3960 presents an excess of the stellar density over King's profile (Rcore = 0.62 ± 0.11 pc and Rlim = 6.0 ± 0.8 pc) at the center. The tidal radii of M 52 and NGC 3960 are Rtidal = 13.1 ± 2.2 pc and Rtidal = 10.7 ± 3.7 pc. Cluster ages of M 52 and NGC 3960 derived with Padova isochrones are constrained to 60 ± 10 Myr and 1.1 ± 0.1 Gyr. In M 52 the core MF ( χcore = 0.89 ± 0.12) is flatter than the halo's ( χhalo = 1.65 ± 0.12). In NGC 3960 they are χcore = -0.74 ± 0.35 and χhalo = 1.26 ± 0.26. The mass locked up in MS/evolved stars in M 52 is ˜1200 Mo; and the total mass (extrapolated to 0.08 Mo) is ˜3800 Mo. The total mass in NGC 3960 is ˜1300 Mo. Conclusions. Compared to open clusters in different dynamical states studied with similar methods; the core and overall parameters of M 52 are consistent with an open cluster more massive than 1000 M o and ˜60 Myr old; with some mass segregation in the inner region. The core of NGC 3960 is in an advanced dynamical state with strong mass segregation in the core/halo region; while the somewhat flat overall MF ( χ 1.07) suggests low-mass star evaporation. The excess stellar density in the core may suggest post-core collapse. The dynamical evolution of NGC 3960 may have been accelerated by the tidal Galactic field; since it lies 0.5 kpc inside the Solar circle. © ESO 2006;
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页码：931 / 942
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