CH₄on−CH₄off vs. J − H, J − K and H − K for the point-like objects detected in Serpens Core (small grey dots). The circles with error bars are the T-dwarf candidates in this study; their ID number is indicated. The squares and triangles show the location of confirmed field L and T dwarfs, respectively (Chiu et al. 2006; Golimowski et al. 2004; Knapp et al. 2004). The position of the CFHT_J0344+3206 mid-T dwarf candidate (green diamond) is plotted for comparison. The lines show the 5 Gyr and 3 Myr COND isochrones (dashed lines) and the 5 Gyr and 3 My DUSTY isochrones (continuous line), as indicated in the labels. The extinction vector is shown for A_V = 10 mag.