Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993aas...18111604e&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #116.04; Bulletin of the American Astronomical Society, Vol. 25, p.734
Astronomy and Astrophysics
Astronomy
Scientific paper
The optical and infrared continuum emission excesses in classical T Tauri stars are frequently attributed to accretion disks with characteristic mass accretion rates of 10(-7) Msun yr(-1) . In the presence of strong stellar magnetic fields, inferred from x-ray fluxes and spot properties, coupling between the accretion disk and the stellar magnetosphere is predicted to 1) control the structure of the boundary layer interface between the disk and the star and 2) regulate the stellar angular velocity at a value an order of magnitude below break-up. One observable consequence of magnetospherically controlled boundary layers is a large radial infall velocity, as material free falls from the point in the disk corresponding to the Alfven radius, channeled along magnetic field lines, to the stellar surface. We have conducted a high resolution spectroscopic survey of classical T Tauri stars covering a broad range of inferred disk accretion rates to determine the frequency of inverse P Cygni line profiles, which diagnose material infalling at velocities of several hundred km/sec. By extracting residual emission line profiles, with photospheric and telluric lines removed, we can delineate the weak extended wings of broad emission lines whose velocity structure cannot be determined on the original spectra. Our major findings are: (1.) Mass infall signatures are present in > 90% of our sample, which includes objects covering the full range of infrared and optical continuum excesses characterizing classical T Tauri stars. (2.) Mass infall signatures are found in many atomic species, including higher Balmer lines, Na D, Mg I, Fe I, Fe II, He I, and He II. (3.) Mass infall signatures are observed among stars with a broad range of inclinations of their rotational axes, as inferred from combining rotational periods and vsini measurements. We conclude that our data strongly support the idea that a sizable stellar dipole field controls disk accretion onto the stellar surface in a manner analogous to that described by Ghosh and Lamb for accretion disks around neutron stars.
Edwards S. S.
Hartigan Patrick
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