All Figures

$\begin{figure} \par\includegraphics[width=14cm,height=10cm]{0642fig1.eps}\end{figure}$ Figure 1: A map of the North America Nebula region. The region of NGC 6996 covered by our study is marked by a dashed square (see also Fig. 3). North is up, East to the left.
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In the text

$\begin{figure} \par\includegraphics[width=7.5cm]{0642fig2.eps}\end{figure}$ Figure 2: DAOPHOT errors in the colour indexes and V magnitude as a function of V.
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In the text

$\begin{figure} \par\includegraphics[width=12cm]{0642fig3.eps}\end{figure}$ Figure 3: Finding chart of the NGC 6996 region (V filter). The black solid circle indicates the adopted angular size (radius = $7^{\prime }$ ) for the cluster (see Sect. 3.1 and Fig. 5). Adopted likely and probable cluster members are enclosed in small circles and triangles, respectively. For a coordinate reference, the center (X = 0; Y=0) corresponds to the cluster coordinates (see Sect. 3.1) and each X-Y are expressed in arcsecs. North is up, East to the left.
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In the text

$\begin{figure} \par\includegraphics[width=13.75cm]{0642fig4.eps}\end{figure}$ Figure 4: Spectra of some bright stars in the field of NGC 6996. A few interesting lines are indicated. See Table 2 for details. Numbers correspond to the Zdanavicius & Straizys (1990) identification.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm]{0642fig5.eps}\end{figure}$ Figure 5: Stellar density in the region of NGC 6996 as a function of the radius from 2MASS and DSS-2 red data. The dashed line indicates the adopted limit for the cluster.
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In the text

$\begin{figure} \par\includegraphics[width=7.75cm]{0642fig6.eps}\end{figure}$ Figure 6: Vector point diagram for the stars $10^{\prime }$ around the center of NGC 6996 (data from Tycho-2 catalogue). See Fig. 7 caption for the meaning of the symbols. The cross indicates the mean error values.
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In the text

$\begin{figure} \par\includegraphics[height=10cm]{0642fig7.eps}\end{figure}$ Figure 7: Color-color diagrams (CCDs) of stars in the region of NGC 6996. a) U-B vs. B-V diagram. Symbols have the following meaning: circles are likely member stars (lm), triangles are probable member stars (pm), white squares are non-members (nm) and small hollow circles are stars without any membership assignment. The solid line is the Schmidt-Kaler's (1982) ZAMS, whereas the dashed lines are the same ZAMS, but shifted by E_B-V = 0.43 and 0.65, respectively (see also Fig. 10a). The dashed arrow indicates the reddening path. b) B-V vs. V-I diagram. Symbols as in Fig. 7a. Solid lines are the intrinsic positions for stars of luminosity classes V and III (Cousins 1978a,b). The two dashed lines give the typical excess ratio for the Cygnus region ( E_V-I / E_B-V = 1.25) and that adopted for the cluster ( E_V-I / E_B-V = 1.69).
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In the text

$\begin{figure} \par\includegraphics[height=10cm]{0642fig8.eps}\end{figure}$ Figure 8: Color-magnitude diagrams (CMDs) for all the stars covered in the field of NGC 6996. Symbols as in Fig. 7a. The solid line is the Schmidt-Kaler (1982) empirical ZAMS shifted by the apparent distance modulus V-M_V = 11.2 ( $V-M_{V} = V_{0}-M_{V} + 4.1 \times (E_{B-V})$ , see Sect. 4).The dashed curves are the isochrones from Girardi et al. (2000). The reported numbers give the $\log~(age)$ .
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In the text

$\begin{figure} \par\includegraphics[height=9.25cm]{0642fig9.eps}\end{figure}$ Figure 9: CMDs from the 2MASS catalog. Symbols as in Fig. 7a. a) Stars placed inside the cluster area ( $R < 7^{\prime }$ , see Fig. 5). b) Stars located in the comparison field around the cluster ( $R > 8\hbox {$.\mkern -4mu^\prime $ }85$ and inside a box $20^{\prime } \times 20^{\prime }$ ). The solid line in panel a) and the dotted one in panel b) are the intrinsic position for MS stars from the Schmidt-Kaler (1982) and Koorneef (1983) calibrations fitted to the apparent distance modulus K-M_K = 9.6 ( K-M_K = V₀-M_V + (3.1-2.78) (4.1/3.1) E_B-V, see Sect. 4). The dashed curves are the isochrones from Girardi et al. (2000). The reported numbers give the $\log~(age)$ .
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In the text

$\begin{figure} \par\includegraphics[width=7.5cm,height=16cm]{0642fig10.eps}\end{figure}$ Figure 10: a) E_B-V distribution for stars inside the $7^{\prime }$ cluster radius (white histogram) and for adopted likely and probable cluster members (dashed histogram). b) E_U-B vs. E_B-V diagram for stars with available spectral classification. c) E_V-I vs. E_B-V diagram. d) Variable extinction method. Symbols in panels b), c) and d) as in Fig. 7a. Dashed lines represent normal relations and solid ones those obtained for NGC 6996.
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In the text

$\begin{figure} \par\includegraphics[width=13cm]{0642fig11.eps}\end{figure}$ Figure 11: The color difference method. a) Solid lines are individual curves computed for stars with spectral classification and luminosity class V (see Table 2). b) Solid line is the obtained average curve together with their extrapolation up to $1/\lambda _{\rm eff} = 0$ . Dotted lines with grey simbols in both panels are the extinction curve # 15 from van de Hulst (Johnson 1968).
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In the text

$\begin{figure} \par\includegraphics[height=10cm]{0642fig12.eps}\end{figure}$ Figure 12: V₀ vs. (B-V)₀ diagram of the likely and probable member stars in the region of NGC 6996. Symbols as in Fig. 7a. Solid and dotted lines are the Schmidt-Kaler (1982) ZAMS shifted by the adopted distance modulus V₀ - M_V = 9.4 and the 0.75 envelope limit for binaries. Dashed curves are the isochrones from Girardi et al. (2000). Numbers give the $\log~(age)$ .
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In the text

$\begin{figure} \par\includegraphics[width=14cm,height=10cm]{0642fig1.eps}\end{figure}$	Figure 1: A map of the North America Nebula region. The region of NGC 6996 covered by our study is marked by a dashed square (see also Fig. 3). North is up, East to the left.
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$\begin{figure} \par\includegraphics[width=7.5cm]{0642fig2.eps}\end{figure}$	Figure 2: DAOPHOT errors in the colour indexes and V magnitude as a function of V.
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$\begin{figure} \par\includegraphics[width=13.75cm]{0642fig4.eps}\end{figure}$	Figure 4: Spectra of some bright stars in the field of NGC 6996. A few interesting lines are indicated. See Table 2 for details. Numbers correspond to the Zdanavicius & Straizys (1990) identification.
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$\begin{figure} \par\includegraphics[width=8.8cm]{0642fig5.eps}\end{figure}$	Figure 5: Stellar density in the region of NGC 6996 as a function of the radius from 2MASS and DSS-2 red data. The dashed line indicates the adopted limit for the cluster.
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$\begin{figure} \par\includegraphics[width=7.75cm]{0642fig6.eps}\end{figure}$	Figure 6: Vector point diagram for the stars $10^{\prime }$ around the center of NGC 6996 (data from Tycho-2 catalogue). See Fig. 7 caption for the meaning of the symbols. The cross indicates the mean error values.
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$\begin{figure} \par\includegraphics[width=13cm]{0642fig11.eps}\end{figure}$	Figure 11: The color difference method. a) Solid lines are individual curves computed for stars with spectral classification and luminosity class V (see Table 2). b) Solid line is the obtained average curve together with their extrapolation up to $1/\lambda _{\rm eff} = 0$ . Dotted lines with grey simbols in both panels are the extinction curve # 15 from van de Hulst (Johnson 1968).
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$\begin{figure} \par\includegraphics[height=10cm]{0642fig12.eps}\end{figure}$	Figure 12: V₀ vs. (B-V)₀ diagram of the likely and probable member stars in the region of NGC 6996. Symbols as in Fig. 7a. Solid and dotted lines are the Schmidt-Kaler (1982) ZAMS shifted by the adopted distance modulus V₀ - M_V = 9.4 and the 0.75 envelope limit for binaries. Dashed curves are the isochrones from Girardi et al. (2000). Numbers give the $\log~(age)$ .
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