2026/06/17 by S. G. Ansari
Physics and Astronomy · #astro-ph.SR #astro-ph.GA
We test whether the peculiar (bulk-subtracted) proper-motion directions of young stellar objects (YSOs) show a preferred orientation relative to the plane-of-sky magnetic field of their natal cloud, and whether such behaviour is universal or cloud dependent. For 2160 YSOs in seven nearby clouds (Chamaeleon I, Perseus, Ophiuchus, Orion A South and North, Taurus, Lupus) we cross-matched published membership catalogues with Gaia DR3. Bulk motion was removed per kinematic subgroup by subtracting the mean space velocity including the perspective term; the residual peculiar proper motion was compared with the Planck 353 GHz plane-of-sky field. Alignment was quantified with the Projected Rayleigh Statistic (Zx) and a Kuiper test. Using total proper motions, every cloud shows a spurious preferred orientation (Zx\rm tot up to +16.5). After bulk removal the picture changes qualitatively: Orion A South and North show significant perpendicular orientation (Zx=-4.4, -6.7), Perseus shows significant alignment (Zx=+3.9), and Chamaeleon I, Taurus, Ophiuchus and Lupus are consistent with isotropy. The apparent `universal alignment' seen in the raw motions is a bulk-motion artefact. Frame-corrected YSO peculiar motions thus retain a measurable but heterogeneous relationship to the natal field, consistent with stars inheriting the velocity field of field-organised natal gas rather than being dynamically steered by the field.