We present recent measurements of the orbital motion in the binaries , DF Tau and ZZ Tau , and in the triples , Elias 12 , T Tau , and V853 Oph .
We observed these systems with the Fine Guidance Sensors on the Hubble Space Telescope and with adaptive optics imaging at the W. M. Keck and Gemini North Observatories .
Based on our measurements and those presented in the literature , we perform preliminary orbital analyses for DF Tau , ZZ Tau , Elias 12 Na-Nb , and T Tau Sa-Sb .
Because the orbital coverage in most of these systems does not yet span a sufficient portion of the orbit , we are not able to find definitive orbit solutions .
By using a Monte Carlo search technique , we explored the orbital parameter space allowed by the current set of data available for each binary .
We constructed weighted distributions for the total mass of the binaries derived from a large sample of possible orbits that fit the data .
These mass distributions show that the total mass is already well-defined .
We compute total mass estimates of 0.78 ^ { +0.25 } _ { -0.15 } M _ { \odot } , 0.66 ^ { +0.15 } _ { -0.11 } M _ { \odot } , 1.13 ^ { +0.36 } _ { -0.09 } M _ { \odot } , and 4.13 ^ { +1.58 } _ { -0.97 } M _ { \odot } for DF Tau , ZZ Tau , Elias 12 Na-Nb , and T Tau Sa-Sb respectively , using a distance of 140 pc .
For Elias 12 Na-Nb , where the orbital coverage spans \sim 164 ^ { \circ } , we compute a preliminary orbit solution with a period of \sim 9-12 years .
By including an earlier lunar occultation measurement , we also find a likely orbit solution for ZZ Tau , with a period of \sim 32 years .
With additional measurements to continue mapping the orbits , the derived dynamical masses will be useful in constraining the theoretical tracks of pre-main sequence evolution .