  The compact, non-thermal emission in DoAr21 has been studied with the VLBA to
investigate the possibility that the residuals of the astrometry fitting are
due to the reflex motion induced by a possible companion. We find that the
fitting of VLBA astrometric observations of DoAr21 improves significantly by
adding the orbital motions of three companions. We obtain an improved distance
to the source of $134.6\pm1.0$ pc, and estimate that the central star, DoAr21,
has a mass of about $2.04\pm0.70~M_{\odot}$. We suggest that DoAr21 represents
a unique case where two sub-stellar companions, DoAr21b and DoAr21c ($m_{b}\sim
35.6\pm27.2~M_{jup}$ and $m_{c}\sim44.0\pm13.6~M_{jup}$, respectively), have
been found associated to a relatively low mass, pre-main sequence star. In
addition, we find that this WTTau star is an astrometric double system, having
a low-mass star companion, DoAr21$B$ ($m_{B}\sim0.35\pm0.12~M_{\odot}$), in a
relatively eccentric orbit. The orbit of this low-mass stellar companion is
compact, while the Brown Dwarfs are located in external orbits. DoAr21$c$ has
the strongest astrometric signature in the periodogram, while DoAr21$B$ has a
weak but significant signature. On the other hand, the astrometric signature of
DoAr21$b$ does not appear in the periodogram, however, this Brown Dwarf was
directly detected in some of the VLBA observations. The estimated orbital
periods of DoAr21$B$, DoAr21$b$ and DoAr21$c$ are $P_{B}\sim92.92\pm0.02$,
$P_{b}\sim450.9\pm3.8$ and $P_{c}\sim1013.5\pm25.3$ days, respectively. Since
the estimated age of this young star is about 0.4$-$0.8 Myrs, the detected
Brown Dwarf companion is among the youngest companions observed to date.
