Spectropolarimetry of Magnetospheric Accretion on the Classical T Tauri Star BP Tauri

High-resolution (R ≈ 60,000) circular spectropolarimetry of the classical T Tauri star BP Tauri is presented. No net polarization is detected in photospheric absorption lines, placing strong limits (3 σ) on the mean longitudinal magnetic field (±200 G) that is present over the surface of the star. On the other hand, strong circular polarization is measured in the He I λ5876 emission line of BP Tau, indicating a mean longitudinal magnetic field of 2460±120 G in the line formation region. This implies that accretion occurs preferentially along large-scale magnetic loops that occupy a small fraction of the stellar surface. These observations represent the first direct evidence for magnetically controlled accretion onto classical T Tauri stars.

[1]  Andrew Collier Cameron,et al.  Spectropolarimetric observations of active stars , 1997 .

[2]  J. Valenti,et al.  Detection of Strong Magnetic Fields on M Dwarfs , 1995 .

[3]  Phillip J. MacQueen,et al.  THE HIGH-RESOLUTION CROSS-DISPERSED ECHELLE WHITE PUPIL SPECTROMETER OF THE MCDONALD OBSERVATORY 2.7-M TELESCOPE , 1995 .

[4]  J. Valenti,et al.  Infrared Zeeman Analysis of epsilon Eridani , 1995 .

[5]  P. Hartigan,et al.  Spectroscopic evidence for magnetospheric accretion in classical T Tauri stars , 1994 .

[6]  Nuria Calvet,et al.  Magnetospheric accretion models for T Tauri stars. 1: Balmer line profiles without rotation , 1994 .

[7]  J. Valenti,et al.  T Tauri stars in blue , 1993 .

[8]  G. Marcy,et al.  Limits on the Magnetic Flux of a Pre-Main Sequence Star , 1992 .

[9]  A. Koenigl.  Disk accretion onto magnetic T Tauri stars , 1991 .

[10]  M. Camenzind.  Magnetized Disk-Winds and the Origin of Bipolar Outflows. , 1990 .

[11]  C. Bertout,et al.  Accretion Disks around T Tauri Stars , 1988 .

[12]  S. Saar.  Improved Methods for the Measurement and Analysis of Stellar Magnetic Fields , 1988 .

[13]  R. Johnstone,et al.  Follow-up Zeeman observations of the T Tauri Star RU Lup , 1987 .

[14]  J. T. Hoeksema,et al.  An atlas of photospheric magnetic field observations and computed coronal magnetic fields: 1976–1985 , 1986 .

[15]  R. Johnstone,et al.  A search for magnetic fields in the T Tauri stars GW Ori, CoD-34 7151, and RU Lup , 1986 .

[16]  J. Landstreet,et al.  A search for weak longitudinal magnetic fields on late-type stars , 1981 .

[17]  S. Vogt.  A magnetic study of spotted UV Ceti flare stars and related late-type dwarfs , 1980 .

[18]  Jr. Robinson.  Magnetic field measurements on stellar sources - A new method , 1980 .

[19]  S. Vogt,et al.  Performance of the Zeeman analyzer system of the McDonald Observatory 2.7 meter telescope , 1980 .

[20]  J. Landstreet,et al.  The magnetic field geometry of HD 215441 , 1978 .

[21]  H. W. Babcock.  The 34-KILOGAUSS Magnetic Field of HD 215441. , 1960 .