All Figures

	Figure 1: The Palomar (rectangles) and Calar (squares) photometric surveys carried out in the Praesepe ( left panel) and  Orionis ( right panel) star open clusters. Solid squares correspond to candidates with high photometric cluster membership probability, and open circles stand for low probability candidates. Bottom images are taken from the Digital Sky Survey (DSS1, red data).
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In the text

Figure 2: Optical color-magnitude diagramas of our Palomar ( left) and Calar ( right) surveys in the Praesepe star cluster. Selected Praesepe candidates are plotted as filled circles. Previously known members, which are labeled, define the cluster photometric sequence depicted with a dashed line. The solid lines indicate the limiting magnitudes of our surveys; completeness is about 1 mag brighter. Masses for an age of 500 Myr are indicated to the right side of the diagrams. Note that only PSF photometric errors are plotted.

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In the text

Figure 3: Optical color-magnitude diagramas of our Palomar ( left) and Calar ( right) surveys in the  Orionis star cluster. Selected  Orionis candidates are plotted as filled circles. Previously known members, which are labeled, define the cluster photometric sequence depicted with a dashed line. The solid lines indicate the limiting magnitudes of our surveys; completeness is about 1 mag brighter. Masses for an age of 3 Myr are indicated to the right side of the diagrams. Note that only PSF photometric errors are plotted.

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In the text

Figure 4: Our Praesepe ( left panel) and  Orionis ( right panel) candidates in the optical color-magnitude diagram. Filled circles stand for the newly discovered cluster candidates with high membership probability, while previously known cluster members are plotted as open circles. Our "less'' probable member candidates are depicted with open triangles (they lie in a sequence that appears slightly bluer than those of the clusters). Overplotted onto the data are the 500-Myr (Praesepe) and 3-Myr ( Orionis) isochrones (solid lines) from the Lyon group (Chabrier et al. 2000; Baraffe et al. 1998, 2003). Masses in Jovian units are indicated to the right of the diagrams. The field sequence of late-M and L-type dwarfs at the distance of the Praesepe cluster is plotted as a dotted line in the left panel (spectral types are labeled). Note that only PSF photometric errors are shown.

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In the text

Figure 5: Near-infrared color-magnitude diagram of Praesepe members. Our "low'' and "high'' new optical candidates with photometry are plotted as open triangles and filled circles, respectively, along with their associated error bars. Previously known members and data from the literature are shown with open circles. The field sequence at the distance of the cluster is plotted as a solid line (spectral types are labeled). Masses according to an age of 500 Myr and the models by Chabrier et al. (2000) are indicated to the right side of the diagram.

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In the text

Figure 6: Optical and near-infrared color-magnitude diagram of  Orionis members. Our candidates with i'z' high photometric membership probability are plotted as filled circles, open triangles stand for low probability ones. Previously identified cluster members are shown with open circles. Overplotted onto the data is the 3-Myr isochrone from Chabrier et al. (2000) and Baraffe et al. (2003). Masses are labeled to the right.

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In the text

	Figure 7: Images ( in extent) of Prae J084111.9+192043 taken at four different wavelengths.
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In the text

Figure 8: Praesepe (500 Myr, left panel) and  Orionis (3 Myr, right panel) mass functions from stars to substellar objects. The results from our surveys are depicted with filled dots and histograms. Error bars are Poissonian. In the left panel, we have also plotted the Praesepe stellar mass functions from Adams et al. (2002, solid line) and Hambly et al. (1995a, dotted line). In both panels, and for comparison purposes, the  Orionis mass function of Caballero (2006) is shown with a dashed line. It is conveniently scaled to the stellar (Praesepe) and substellar ( Orionis) regimes. Vertical dotted lines correspond to the hydrogen (0.075 ) and deuterium (0.012 ) burning-mass limits.

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In the text

	Figure 9: Finding charts (z'-band, in extent) of Praesepe candidates labeled with a "high'' photometric cluster membership probability.
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In the text

	Figure 10: Finding charts (z'-band, in extent) of Praesepe candidates labeled with a "low'' photometric cluster membership probability.
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In the text

	Figure 11: Finding charts (z'-band, in extent) of  Orionis candidates labeled with a "high'' photometric cluster membership probability.
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In the text

	Figure 12: Finding charts (z'-band, in extent) of  Orionis candidates labeled with a "low'' photometric cluster membership probability.
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In the text