2016MNRAS.463.3563T

Using Atacama Large Millimeter/submillimeter Array observations of the C¹⁸O(2-1) line emission of the gas envelope of protostar L1527, we have reconstructed its morphology and kinematics under the assumption of axisymmetry about the west-east axis. The main original contribution to our understanding of the formation process of L1527 is the presentation of a simple 3D parametrization based solely on regions that are not dominated by absorption. In the explored range (∼0.7 to 5 arcsec from the star), the model reproduces observations better than earlier attempts. The main results include: a measurement of the rotation velocity that confirms its evolution to Keplerian towards short distances; a measurement of the mean in-fall velocity, 0.43 ± 0.10 km s^–1, lower than free-fall velocity, with no evidence for the significant r-dependence suggested by an earlier analysis; a measurement of the central mass, 0.23 ± 0.06 M_☉ within a distance of 1.5 arcsec from the star, in agreement with earlier estimates obtained from a different range of distances; evidence for a strong disc plane depression of the in-falling flux resulting in an X-shaped flow possibly caused by the freeze-out of CO molecules on dust grains; a measurement of the accretion rate, 3.5 ± 1.0 10^–7 M_☉ yr^–1at a distance of 1 arcsec (140 au) from the star; evidence for a 10° tilt of the symmetry plane of the envelope about the line of sight, cancelling below ∼3 arcsec from the star, but matching infrared observations and being also apparent on the sky map of the mean Doppler velocity.