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R. J. White, L. A. Hillenbrand (CalTech)
We present high resolution optical spectra obtained with the HIRES spectrograph on the W. M. Keck I telescope of the youngest optically visible stars in Taurus-Auriga. The observed sample consist of 13 Class I protostars and 22 Class II or transitional Class I/II stars; the Class I and I/II stars observed are all in systems that power Herbig-Haro flows. For 27 of these 35 stars, these measurements are the first high dispersion spectra ever obtained. Photospheric features are detected in 9 of the Class I stars and all of the Class II and I/II stars; strong emission lines (e.g. H-alpha) are detected in the spectra of all stars. These measurements are used to determine the stellar properties (effective temperatures, masses, relative surface gravities, rotational and radial velocities) and circumstellar properties (mass accretion and outflow rates) of this unprecedentedly young sample. Several Class I stars have spectral types cooler than M5 and therefore may be Class I brown dwarfs. The inferred masses of the Class I stars are, in several cases, significantly different from previous estimates derived by assuming an accretion dominated luminosity. The youngest stars (e.g. Class I-like) appear to have both higher mass accretion and outflow rates than older stars (e.g. Class II-like). Their rotational velocities, however, are not significantly different. The combined results are used to assess the validity of the popular Class I/II/III classification scheme as a measure of stellar age.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.