8 Comparison with NIR observations

  From 510 objects from the deep near-infrared survey of Lada & Lada (1995) in their survey area indicated in Fig. 1 we were able to identify 44 optical counterparts in our sample of 1431 stars using a search radius of 2arcsec. For 41 of these stars the proper motion errors are < 10mas/yr, for 28 stars they are < 5mas/yr. If we define the cluster members with proper motion membership probabilities > 50% and the foreground stars, respectively with small membership probabilities of both cluster stars and distant field stars ($P_{\rm cl} < 5$% and $P_{\rm df} < 5$%) we get 30 IC348 members and 5 foreground stars among the optical counterparts of NIR sources.

  

Figure 14: Near-infrared two colour diagram for 510 objects (dots) from Lada & Lada (1995). From 44 objects with optical counterparts in our sample of 1431 stars (search radius 2arcsec) those with proper motion cluster membership probabilities $P_{\rm cl} \gt 50$% (30 objects) are overplotted as open triangles whereas the 5 proper motion foreground stars (cluster membership probabilities $P_{\rm cl} < 5$% and distant field stars membership probabilities $P_{\rm df} < 5$%) are overplotted as open circles

Figure 14 shows the location of these optical counterparts in the two-colour diagram of Lada & Lada (1995). One can see that the proper motion members of IC348 tend to be redder in both colours (H-K) and (J-H), but especially in (J-H) in comparison to the foreground stars. The members show also a larger dispersion in their colours than the foreground stars. This is in agreement with the comparison of the NIR photometry of Lada & Lada (1995) in the field of IC348 with two control fields outside the one square degree region around IC348.

If we allow for a larger uncertainty in the positions of the NIR sources, e.g. using search radii of 3 and 4 arcmin, we identify 70 and 97 sources, respectively.