Other
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...18110311v&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #103.11; Bulletin of the American Astronomical Society, Vol. 24, p.1288
Other
Scientific paper
Using well measured Balmer jumps and emission line strengths, we discuss the origin of excess optical emission from classical T Tauri stars. We present a selection of moderate resolution, moderate S/N, flux--calibrated, blue spectra from our sample of 97 T Tauri stars. They illustrate the range of observed emission levels. The spectra extend from 3400 Angstroms to 5000 Angstroms, and they include the Balmer jump and the entire Balmer series except for Hα . We detail a new method of measuring Balmer jumps that uses a spectral model to infer the true jump, rather than attempting to measure it directly from the spectrum. A weak T Tauri star of similar spectral type is used to remove the photospheric contribution from our CTTS spectra. The remaining ``excess'' emission is then modelled as an isothermal rectangular slab of hydrogen projected against the star. A simple slab of hydrogen does a remarkably good job of explaining continuum and high Balmer line (beyond Hdelta ) emission. The continuum shape and flux, including the magnitude of the Balmer jump are well matched for most of the CTTS in our sample. The role of H(-) \ is critical in mediating the size of the Balmer jump. Because H(-) \ emission is sensitive to density, we believe that most of the continuous optical excess emission in CTTS arises from gas at a density of roughly 10(14) \ cm(-3) . The continuous emission from the hydrogen slab also serves to weaken or ``veil'' photospheric absorption lines in accordance with our observations. The general behavior and strength of the high Balmer lines can be reproduced by a slab model. The low Balmer lines, however, have considerable excess emission beyond that arising from the isothermal slab, which we take as evidence for a lower density component, perhaps arising in a wind. We also discuss the relationship between the Balmer jump and various other measures of excess emission.
Basri Gibor B.
Valenti Jeff A.
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