The pre-main-sequence binary T Tauri was observed in 1991 September using a simultaneous combination of the Very Large Array (VLA) and a four-antenna Very Long Baseline Interferometry (VLBI) array operating at λ = 18 cm. Strong circular polarization (25%-30%) was detected in the VLA measurements, and there was evidence for variations in both circular polarization V and total intensity / on time scales of 1 hr. VLBI measurements of T Tauri taken in parallel failed to detect any compact flux density, despite having sufficient sensitivity to measure fringe visibilities as faint as 15% of the total flux density from the source. If the radiation from T Tau resembles that from other stellar radio sources in circular polarization fraction n, the VLBI measurements imply a lower limit on the size of unpolarized radiation of ∼ 1 AU or 70 stellar radii. The circular polarization and rapid flux variations indicate a significant nonthermal contribution in the radio emission from T Tau, previously thought to be solely thermal free-free radiation from stellar winds or inflows. Reanalysis of high-resolution 1983 VLA data implicates the protostar T Tau(S) as the probable source of the circular polarization. It thus appears to be the first protostar system to show nonthermal radio activity, previously documented to be present around weak-lined T Tauri stars (e.g., Phillips, Lonsdale, & Feigelson 1991).
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science