SIMBAD references

We present a high-resolution image of the region near HL Tau in ¹³CO (1-0) over a region of 3' made with the BIMA array, supplemented by data from the NRAO 12 m telescope to include emission structures with low spatial frequencies. We find evidence for a shell of dimensions ∼2'x1'.5 (∼0.08x0.06 pc), with XZ Tau being the closest known source to its center. The ¹³CO map is consistent with an expanding bubble that has blown out on the far side from earth. Portions of the bubble wall are seen in optical scattered light. HL Tau is situated in the bubble wall; the evacuated region corresponds to the truncation in the reflection nebula northeast of HL Tau. Although it is thought that a remnant protostellar envelope is still infalling onto HL Tau, the existence of the expanding bubble makes it difficult to interpret the geometry and kinematics of the HL Tau circumstellar material. Our results demonstrate the importance of including low-spatial frequency emission for the interpretation of interferometer maps.