Accurate proper motions of the protostellar system VLA 1623−2417

ABSTRACT We present a detailed astrometric analysis of the quadruple protostellar system VLA 1623−2417, deriving accurate absolute proper motions for components A, B, and W, as well as, for the first time, individual motions for the compact binary components of VLA 1623−2417 A (Aa and Ab). Our study combines 37 archival interferometric observations from the Atacama Large Millimeter/submillimeter Array (ALMA) and the Karl G. Jansky Very Large Array (VLA) at centimetre and millimetre wavelengths, supplemented with additional data from the Submillimeter Array (SMA) and the Berkeley–Illinois–Maryland Association (BIMA) millimetre array taken from the literature. Together, these data provide time baselines of $\sim$34.5 yr for component B, $\sim$32.5 yr for component W, and $\sim$11 yr for the individual components Aa and Ab. The relative proper motions of Aa/Ab indicate significant orbital motions, but cover too small a fraction of the orbit to provide a reliable mass estimate. The relative proper motions of W with respect to components A and B indicate that W is approaching A/B at a projected speed of 1−2 km s$^{-1}$. These inward motions are inconsistent with scenarios in which component W has been dynamically ejected from the VLA 1623−2417 system. Instead, we argue that W is either not bound to the A/B components or is moving on a highly inclined orbit.