EDP Sciences
Free access
Volume 375, Number 2, August IV 2001
Page(s) 485 - 491
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20010442

A&A 375, 485-491 (2001)
DOI: 10.1051/0004-6361:20010442

Coronal structure geometries on pre-main sequence stars

F. Favata1, G. Micela2 and F. Reale3

1  Astrophysics Division -Space Science Department of ESA, ESTEC, Postbus 299, 2200 AG Noordwijk, The Netherlands
2  Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
3  Dip. Scienze FF. & AA., Sez. Astronomia, Univ. Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy

(Received 15 January 2001 / Accepted 21 March 2001)

Using a hydrodynamic model we have re-analyzed large flaring events on three different categories of pre-main sequence (PMS) stars: the young stellar object (YSO) YLW 15, the classical T Tauri star (CTTS) LkH$\alpha$ 92, the weak-line T Tauri star (WTTS) V773 Tau, and the WTTS HD 283572 (the first three objects were observed by ASCA, the last by ROSAT; all observations have been previously reported in the literature). The first three flares were previously analyzed on the basis of a quasi-static model mostly used up to now, consistently yielding large loops ($L \ga R_*$) and no evidence of sustained heating. Our hydrodynamic modeling approach, however, shows that the size of the flaring regions must be much smaller ($L \la R_*$) and moreover this method shows in all cases evidence of vigorous sustained heating during the flare decay, so that the decay of the observed light curve actually reflects the temporal profile of the heating rather than that of the free decay of the heated loop(s). The events on the protostar YLW 15 have durations comparable to the stellar rotation period, so that their limited size and their lack of self-eclipses give evidence of a polar location on the star. This is in contrast with the recently advanced hypothesis that these flares are due to long loops spanning the region between the star and the accretion disk. In general, the present analysis shows that flaring coronae on PMS stars have a structure similar to the coronae on older active stars.

Key words: stars: late-type -- activity -- coronae; X-rays: stars

Offprint request: F. Favata, ffavata@astro.esa.int

SIMBAD Objects

© ESO 2001