Parallax fit to the observed data. The upper-left panel shows the observed data and the astrometric fit obtained when fitting only the proper motions and the parallax of DoAr21. The upper-right panel shows the proper motions of the source after removing the parallax of the source. The lower-left panel show the residuals in R.A. and decl., and the lower-right panels show the residuals as function of time. The residuals show a clear temporal trend that suggests that they could be due to at least one companion.