Top: contour plots of the blue (dotted contours, 0.8–6 km s ⁻¹ velocity range) and red (dashed contours, 6–9.5 km s ⁻¹ velocity range) parts of the ¹²CO (2–1) line, superimposed on the contours of the adjacent 1.3 mm continuum (solid contours). Contours are drawn at 22.5%, 45%, and 90% of the peak intensity in each map. The reconstructed beam is shown for comparison. The origin of the relative coordinates is at 04 ^h38 ^m35 51, +26°10′41 5 (J2000), the nominal position of HV Tau C. The inset represents the integrated line profile. Bottom: position–velocity diagram along the disk major axis (indicated by the two solid segments in the top panel). The three-dimensional datacube has been smoothed using a 1 km s ⁻¹×1'' running boxcar function. The contours in the position–velocity diagram are at 15%, 30%, 60%, and 90% of the peak intensity. The dashed curve represents the theoretical Keplerian rotation curve for an 0.7  M _☉ star with v _sys = 5.75 km s ⁻¹. This is not meant as a fit but a reference to guide the eye. The dotted lines indicate the velocity range in which ¹³CO emission from the Taurus molecular cloud was observed by Mizuno et al. (1995) at the location of HV Tau.