2003A&A...402.1003D

We present new single-dish (30-m) observations and an improved analysis of our earlier interferometric observations (Simon et al., 2000ApJ...545.1034S) of BP Tau. Our analysis yields a detailed description of the properties of the circumstellar disk. The disk is small (outer radius 120AU) and marginally optically thick in the ¹²CO J=2->1 line. It is also relatively hot, about 50K at 100AU. The mm continuum emission is consistent with a thermal emission from circumstellar dust with an emissivity index β ≃0.7, and a disk mass about 1.2x10^–3M_☉. The anomalously low ¹²CO to dust emission ratio implies that either CO is depleted by a factor of the order of 150 with respect to H₂, or has a very low gas to dust ratio, or highly anomalous dust properties. The disk exhibits direct evidence of Keplerian rotation, but because of a combination of insufficient resolution and optically thin CO emission, the mass derived for the star remains inaccurate (between 0.6 and 1.3M_☉ for 140pc). The unusual properties of the circumstellar disk suggest that BP Tau may be a transient object in the process of clearing its disk.