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Open clusters in dense fields : the importance of field-star decontamonation for NGC 5715, Lyngå 4, Lyngå 9, Trumpler 23, Trumpler 26 and Czernik 37

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Open clusters in dense fields : the importance of field-star decontamonation for NGC 5715, Lyngå 4, Lyngå 9, Trumpler 23, Trumpler 26 and Czernik 37

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Título Open clusters in dense fields : the importance of field-star decontamonation for NGC 5715, Lyngå 4, Lyngå 9, Trumpler 23, Trumpler 26 and Czernik 37
Autor Bonatto, Charles Jose
Bica, Eduardo Luiz Damiani
Abstract Star clusters projected on to dense stellar fields in general require field-star (FS) decontamination to confirm their nature and derive intrinsic photometric and structural fundamental parameters. This work focuses on the open clusters (OCs) or candidates NGC5715, Lyngå 4, Lyngå 9, Trumpler 23, Trumpler 26 and Czernik 37 which are projected within 317◦ < ~ l < ~ 2◦.2 and |b| < ~ 2◦.8, against crowded bulge and/or disc fields. To tackle these difficult objects we develop a colour–magnitude diagram FS-decontamination algorithm based on 2MASS J, (J − H) and (J − Ks) data, and respective uncertainties, to detect cluster star excesses over the background. On the other hand, colour–magnitude filters are used to build stellar radial density profiles and mass functions. The results convey compelling evidence that Lyngå 9 and Czernik 37 are intermediate-age OCs, and their fundamental parameters are measured for the first time. Trumpler 23 is a particularly challenging object, since besides high background level, its field presents variable absorption in near-infrared bands. We confirm it to be an intermediate-age OC. Trumpler 26 is studied in more detail than in previous works, while NGC5715 and Lyngå 4 have fundamental parameters determined for the first time. These OCs are located 0.9–1.6 kpc within the solar circle, with ages similar to that of the Hyades. Structurally, they are well described by King profiles. In all cases, core and limiting radii are significantly smaller than those of nearby OCs outside the solar circle. We test the effect of background levels on cluster radii determinations by means of simulations. They indicate that for central clusters, radii may be underestimated by about 10–20 per cent, which suggests that the small sizes measured for the present sample reflect as well intrinsic properties related to dynamical evolution effects. The objects probably have been suffering important tidal effects that may have accelerated dynamical evolution, especially in Czernik 37, the innermost object.
Contido em Monthly notices of the royal astronomical society. Vol. 377, no. 3 (May 2007), p. 1301-1323
Assunto Aglomerados abertos e associações
[en] Oopen clusters and associations: individual: Czernik 37
[en] Open clusters and associations: individual: Lyngå 4
[en] Open clusters and associations: individual: Lyngå 9
[en] Open clusters and associations: individual: NGC5715
[en] Open clusters and associations: individual: Trumpler 23
[en] Open clusters and associations: individual: Trumpler 26
Origem Estrangeiro
Tipo Artigo de periódico
URI http://hdl.handle.net/10183/90262
Arquivos Descrição Formato
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