2003AJ....125..858J

Centimeter-wavelength radio observations of the T Tauri system between 1983 and 2001 confirm that the radio emission from the optical star T Tau (T Tau N) has a spectral index of 0.6 and may be attributed to a stellar wind and nonthermal flares that are masked by the thermal emission. Right-circular polarization of 26% is detected in the 2 cm T Tau N emission. The infrared source (T Tau S) is confirmed to be nonthermal and variable in intensity, with a radio spectral index ≤0. T Tau S displays weak extended emission and strong, compact left-circular polarization at wavelengths of 3.7 and 2 cm; the percentage of left-circularly polarized emission is larger at the shorter wavelengths. The 2 cm radio and optical positions of T Tau N are found to be coincident to 13 mas. Relative motion between the two radio sources (T Tau N and S) does not agree in detail with that measured at a wavelength of ∼2 µm. The difference in relative position is as large as 100 mas (15 AU) in declination in the 1980s. The recent IR detection of T Tau S as a binary star with a separation of 50 mas (7 AU) in 1997 December may explain this discrepancy. We suggest a scenario in which the radio emission detected toward T Tau S in our most recent observations (epoch 2001) is located at the position of the less luminous member of this binary system, T Tau Sb. A preliminary estimate of the orbital parameters of this system is an eccentricity of 0.7, semimajor axis 113 mas, inclination 69°, period 38.8 yr, and total system mass 5.3 M_☉. The circular polarization of the centimeter radio emission of T Tau N and T Tau S indicates that the emission from both components is gyrosynchrotron in nature. The opposite sense of circular polarization may indicate that it is dipole in nature.