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 \pm 1.0 pc , and estimate that the central star , DoAr21 , has a mass of about 2.04 \pm 0.70 ~ { } M _ { \odot } .
We suggest that DoAr21 represents a unique case where two sub-stellar companions , DoAr21b and DoAr21c ( m _ { b } \sim 35.6 \pm 27.2 ~ { } M _ { jup } and m _ { c } \sim 44.0 \pm 13.6 ~ { } 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 } \sim 0.35 \pm 0.12 ~ { } 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 } \sim 92.92 \pm 0.02 , P _ { b } \sim 450.9 \pm 3.8 and P _ { c } \sim 1013.5 \pm 25.3 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 .