2018ApJ...865...51T

We present results from our Submillimeter Array (SMA) observations and data analyses of the SMA archival data of the Class I protostar IRAS 04169+2702. The high-resolution (∼0.''5) ¹³CO (3-2) image cube shows a compact (r <= 100 au) structure with a northwest (blue) to southeast (red) velocity gradient, centered on the 0.9 mm dust continuum emission. The direction of the velocity gradient is orthogonal to the axis of the molecular outflow as seen in the SMA ¹²CO (2-1) data. A similar gas component is seen in the SO (6₅-5₄) line. On the other hand, the C¹⁸O (2-1) emission traces a more extended (r ∼ 400 au) component with the opposite, northwest (red) to southeast (blue) velocity gradient. Such opposite velocity gradients in the different molecular lines are also confirmed from direct fitting to the visibility data. We have constructed models of a forward-rotating and counterrotating Keplerian disk and a protostellar envelope, including the SMA imaging simulations. The counterrotating model could better reproduce the observed velocity channel maps, although we could not obtain statistically significant fitting results. The derived model parameters are as follows: Keplerian radius of 200 au, central stellar mass of 0.1 M_☉, and envelope rotational and infalling velocities of 0.20 and 0.16 km s^–1, respectively. One possible interpretation for these results is the effect of the magnetic field in the process of disk formation around protostars, i.e., the Hall effect.