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Astron. Astrophys. 361, 877-887 (2000)

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3. Photometry results

3.1. Components of the clusters

Fig. 1 presents an image of N 11C on which the clusters Sk-66o41 and HNT as well as the main stars are indicated. The outcomes of the deconvolution processing applied to these clusters are displayed in Fig. 2 and Fig. 3, while Table 1 and Table 2 list the results of the photometry.

[FIGURE] Fig. 2. Deconvolved image of the Sk-66o41 cluster, corresponding to the whole blotch appearing in Fig. 1. North is up and east is left. Field 3".9 [FORMULA] 3".9.

[FIGURE] Fig. 3a and b. A close-up of the Strömgren b image (Fig. 1) focused on the HNT cluster. a Original image. b Restored image using the MCS deconvolution method. Field 16".64 [FORMULA] 16".64.

[FIGURE] Fig. 4. Color-magnitude diagrams of the clusters, Sk-66o41 and HNT, and the field stars.

The comparison of the present results for Sk-66o41 with those obtained using an adaptive optics system (Paper II) is interesting. For this purpose, Fig. 2 has the same size as the Fig. 2 in that paper which displays a deconvolved image in the near infrared K band. The similarity is almost perfect, although the present observations reveal 15 components in Sk-66o41 instead of 12. The cross identification between the components of the visible and infrared images is listed in Table 1. The discrepancy in the number of components is due to the fact that the images represent two distinct wavelength ranges and also the clean procedure used for the K image may be partially responsible. Anyhow, the MCS deconvolution code reveals that the core of Sk-66o41 is most probably made up of at least three components (stars #33, #34, and #36). These are all hot stars, as indicated by their colors. The brightest star of the cluster is #36 with [FORMULA].

The HNT cluster is apparently richer than Sk-66o41 but is made up of fainter stars (Table 2, Fig. 3). Only six stars (#66, #78, #85, #91, #105, and #116) appear brighter than y = 17 mag. HNT is generally composed of blue stars, although apart from star #78, all of the six brightest stars have red colors.

3.2. Field stars

The two compact clusters form the densest parts of the LH 13 association (Lucke & Hodge 1970). Photometry was obtained for 344 stars within the field of LH 13 but lying outside the clusters. Several of the brightest ones were also observed spectroscopically, as presented in Sect. 4.

Of particular interest is Wo599. We applied the deconvolution technique to look into its multiplicity, since it has a composite spectrum (see Sect. 4.3). This method did not reveal any close components towards Wo599. The closest stars to Wo599, as shown by the images, are two faint stars of [FORMULA] and [FORMULA] lying at 2".6 west and 2".9 east of Wo599 respectively. This result does not, however, prove that we are dealing with a single star.

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© European Southern Observatory (ESO) 2000

Online publication: January 29, 2001