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Astron. Astrophys. 321, 803-810 (1997)


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Spectrophotometry of flares and short time scale variations in weak line,
and classical T Tauri stars in Chamaeleon

Eike W. Guenther; 1 ,2 and James P. Emerson 2

1 Thüringer Landessternwarte Tautenburg, Karl-Schwarzschild-Observatorium, D-07778 Tautenburg, Germany
2 Department of Physics, Queen Mary & Westfield College, Mile End Road, London E1 4NS, UK

Received 3 September 1996 / Accepted 21 October 1996

Abstract

Results are presented from a monitoring program looking for variations of the equivalent width and flux of [FORMULA], and of the continuum flux, in 18 classical and 18 weak line T Tauri stars, and one Herbig Ae/Be star, on time scales down to 5 minutes. The stars were observed simultaiously for 14 hours using the multiobject-spectrograph FLAIR on the UK Schmidt Telescope. The campaign turned up two events in weak line T Tauri stars. Both events show the characteristics of flares: The increase of the [FORMULA] emission is faster than the decline, and the increase of the emission is much larger in [FORMULA] than in the continuum. The total energies radiated in [FORMULA] are [FORMULA] and [FORMULA], or roughly 200 to 700 times larger than the largest flares on the Sun. The spectrum of one of these events shows a component of [FORMULA] which is blue-shifted by about [FORMULA]. We interpret this component as an indication of mass loss, and estimate, if the event is a typical one, that the mass loss rate due to flares would be about [FORMULA] for a weak line T Tauri star. We derive lower limits to the magnetic flux density of between 10 and 200 G. Although a number of events have been observed in the classical T Tauri stars as well, none of these has shown the strong increase within minutes and decrease in an hour characteristic of a flare. We interpret this result as being due to either an optical thickness effect in [FORMULA], or to the absence of optical flares in classical T Tauri stars, or simply due to failing to catch any flares in classical T Tauri stars.

Key words: stars: pre-main-sequence – stars: flares – stars: magnetic fields – stars: mass loss – stars: emission-line

Send offprint requests to: E. W. Guenther

© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998

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