Spectropolarimetry of the Classical T Tauri Star T Tauri

High-resolution (R ≈ 60,000) circular spectropolarimetry of the classical T Tauri star T Tau is presented. The star was observed on 1997 November 21 and 22. Analyzing 12 photospheric absorption lines, the mean longitudinal magnetic field is found to be B_z = 12 ± 35 G. The 3 σ upper limit of |B_z| ≤ 105 G. Previously, T Tau was reported to have a mean longitudinal field of 160 ± 40 G. A strong mean magnetic field (∼2.4 kG) has been reported on the surface of T Tau based on Zeeman broadening measurements in unpolarized light. The present observations indicate that it is very unlikely that this field is dipolar in nature. In order to verify the observing techniques and analysis methods used on T Tau, spectra of the Sun obtained by observing the asteroid Vesta are analyzed in the same fashion. Here the mean longitudinal field is B_z = -4 ± 3 G, which is well within the limits of previous observations. As a further check on our results, we also present data for the magnetic Ap star 53 Cam, which gives a mean longitudinal magnetic field that agrees well with the published field variations for this star.