\bf Iron Emission Lines in the Spectra of Classical T Tauri Stars

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Session 62 -- Very Young Stars
Display presentation, Thursday, 9:20-4:00, Pauley Room

[62.17] \bf Iron Emission Lines in the Spectra of Classical T Tauri Stars

G.Beristain (Univ. of Mass, Amherst), S.Edwards (FCAD, Univ. of Mass, Amherst), P.Hartigan (FCAD, Univ. of Mass, Amherst)

The optical and infrared continuum emission excesses in classical T Tauri stars are frequently attributed to accretion disks with characteristic mass accretion rates of $10^{-7}$ M$_{\odot}$ yr$^{-1}$. The spectra of classical T Tauri stars are also rich in emission lines, arising from both permitted and forbidden atomic species, which have been attributed to formation in regions as diverse as chromospheres, boundary layers, winds and collimated jets. We have conducted a high resolution spectroscopic survey of 48 T Tauri stars in the Tau-Aur star formation complex covering the wavelength range 3900{\kern.2em\AA} to 7000{\kern.2em\AA} with the aim of determining the origin of the various emission lines and report here on the most prominent metallic species present in the T Tauri spectra, Fe I and Fe II. From our spectra we have both 1) determined the level of optical continuum emission, expressed as the ratio of `veiling' to photospheric flux, and 2) extracted residual Fe emission line profiles, free of contamination from underlying photospheric features.

We find that Fe I, II emission is seen only in T Tauri stars which have infrared and optical continuum emission excesses attributed to accretion disks; none of the `weak-line' T Tauri stars, with photospheric IR colors and no optical veiling, have detectable Fe emission. Correlations of Fe emission equivalent widths with both $K-L$ and the ratio of veiling to photospheric flux, $r$, suggest that the Fe lines arise as a result of accretion related activity.

DR Tau's rich emission line spectra permit study of the largest number of unblended Fe I,II profiles, for which we have spectra covering 5 different nights. Multiplet line ratios indicate the Fe lines are optically thick, and line luminosities imply emitting areas covering a few percent of the stellar surface. The lines are typically broad and symmetric, although inverse P Cygni structure in Fe II is seen on one night. For 4 nights, the Fe I and Fe II lines differ in their FWHM by a factor of two, from 40 to 80 km/sec respectively. We suggest the Fe lines may be formed in magnetospheric accretion columns, coupling the accretion disk to the stellar surface, as described by Konigl (1991) and Calvet and Hartmann (1992).

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