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Astron. Astrophys. 349, L65-L68 (1999)

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5. Conclusions

We have shown that in BP Tau the veiling extracted from low resolution spectra coincides with that derived from high resolution spectra. The calculated veiling of 1 is moderate, but the proposed approach can be applied to higher veiled spectra. Chelli et al. (1999) succeeded to measure veilings as high as 4 from low resolution spectra ([FORMULA]300) of the CTTS DF Tau. This is because the method is based on the energy contained in deep and large scale structures of a few hundreds Angstroms width. A big advantage is that the differences between the object and the template spectra seen at high resolution are minimized or even completely cancelled. Yet, spectra which are highly contaminated with emission lines may be a problem. However, this problem is, to our opinion, as difficult to solve at high spectral resolution, because large spectral mismatches between the object and the template may be present in this case.

The low resolution approach is not meant to replace the high resolution approach and vice versa : we simply do not get the same kind of information. For example, it will probably be difficult to study the spectral variations of the veiling at resolutions as low as a few hundreds only. But on the other hand, the low resolution approach can be a powerful tool, in particular via differential methods, to study variability problems in T Tauri stars, related to e.g. flare or accretion activity (see Chelli et al. 1999), in timescales as short as minutes.

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© European Southern Observatory (ESO) 1999

Online publication: September 13, 1999