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A&A 453, 241-252 (2006)
DOI: 10.1051/0004-6361:20053663

X-ray and optical bursts and flares in YSOs: results from a 5-day XMM-Newton monitoring campaign of L1551

G. Giardino1, F. Favata1, B. Silva1, 2, G. Micela3, F. Reale4 and S. Sciortino3

1  Astrophysics Division - Research and Science Support Department of ESA, ESTEC, Postbus 299, 2200 AG Noordwijk, The Netherlands
    e-mail: Giovanna.Giardino@rssd.esa.int
2  Centro de Astrofisica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
3  INAF - Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
4  Dipartimento di Scienze Fisiche & Astronomiche, Sezione di Astronomia, Piazza del Parlamento 1, 90134 Palermo, Italy

(Received 20 June 2005 / Accepted 15 February 2006)

Abstract
We present the results of a five-day monitoring campaign with XMM-Newton of six X-ray bright young stellar objects (YSOs) in the star-forming complex L1551 in Taurus. All stars present significant variability on the five-day time scale. Modulation of the light curve on time scales comparable with the star's rotational period appeared to be present in the case of one weak-lined T Tauri star. Significant spectral variations between the 2000 and the 2004 observations were detected in the (unresolved) classical T Tauri binary system XZ Tau: a hot plasma component which was present in the X-ray spectrum in 2000 had significantly weakened in 2004. As XZ Tau N was undergoing a strong optical outburst in 2000, which had terminated since then, we speculate on the possible relationship between episodic, burst accretion, and X-ray heating. The transition object HL Tau underwent a strong flare with a complex temperature evolution, which is indicative of an event confined within a very large magnetic structure (few stellar radii), similar to the ones found in YSOs in the Orion Nebula Cluster.


Key words: stars: pre-main sequence -- X-rays: stars -- stars: coronae -- stars: circumstellar matter



© ESO 2006