Index β_t vs. the temperature-sensitive TiO index μ. Heavily veiled CTTS, if present, would fill the empty triangular region, converging toward the point (1,1). The procedure for determination of veiling r is exemplified by the comparison between the black arrow and its gray prolongement; see text for details. At most two-three moderate-veiling stars may be present in this dataset, near μ ~ 1.2.