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Title:
Constraints on the ionizing flux emitted by T Tauri stars
Authors:
Alexander, R. D.; Clarke, C. J.; Pringle, J. E.
Affiliation:
AA(Institute of Astronomy, Madingley Road, Cambridge CB3 0HA; ), AB(Institute of Astronomy, Madingley Road, Cambridge CB3 0HA; ), AC(Institute of Astronomy, Madingley Road, Cambridge CB3 0HA; )
Publication:
Monthly Notices of the Royal Astronomical Society, Volume 358, Issue 1, pp. 283-290. (MNRAS Homepage)
Publication Date:
03/2005
Origin:
MNRAS
MNRAS Keywords:
accretion, accretion discs, planetary systems: protoplanetary discs, stars: pre-main-sequence, ultraviolet: stars
DOI:
10.1111/j.1365-2966.2005.08786.x
Bibliographic Code:
2005MNRAS.358..283A

Abstract

We present the results of an analysis of ultraviolet observations of T Tauri stars (TTs). By analysing emission measures taken from the literature, we derive rates of ionizing photons from the chromospheres of five classical TTs in the range ~1041-1044 photon s-1, although these values are subject to large uncertainties. We propose that the HeII/CIV line ratio can be used as a reddening-independent indicator of the hardness of the ultraviolet spectrum emitted by TTs. By studying this line ratio in a much larger sample of objects, we find evidence for an ionizing flux which does not decrease, and may even increase, as TTs evolve. This implies that a significant fraction of the ionizing flux from TTs is not powered by the accretion of disc material on to the central object, and we discuss the significance of this result and its implications for models of disc evolution. The presence of a significant ionizing flux in the later stages of circumstellar disc evolution provides an important new constraint on disc photoevaporation models.

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