Left:L_bol vs. T_eff for Class III stars and DDs in ρ Ophiuchi cluster with spectral fit to SEDs. Isochrones from Siess et al. (2000) at 1 Myr (dashed line), 5 Myr (dotted line) and 10 Myr (solid line) are traced.Most of the points are comprised betweeen 5 and 10 Myr isochrones. Right panel: L_X/L_bol ratio vs. T_eff for YSOs in the ρ Ophiuchi cluster. Most of the objects lie below the saturation limit of log L_X/L_bol−3 (horizontal line), with the only exception of sources 1 and 61 which are found above it. The cause could be a systematic uncertainty by ~0.6 dex in L_bol or L_X. The points show an overall scatter of about 0.5 dex, and a slight decrease of the L_X/L_bol ratio is visible for T_eff< 3500.