Abstract
The young cluster NGC 2264 was observed with the Corot satellite for 23 days uninterruptedly in March 2008 with unprecedent photometric accuracy. We present here the first results of the analysis of the accreting population. We intended to look for possible light curve variability of the same nature as that observed in the classical T Tauri star AA Tau, which was attributed to a magnetically controlled inner disk warp, which is directly associated with the interaction between the stellar magnetic field and the inner disk region. We analysed the Corot light curves of 83 previously known classical T Tauri stars that belong to NGC 2264 and classified them according to their morphology. We also studied the Corot light curve morphology as a function of a Spitzer-based classification of the star-disk systems. The classification derived on the basis of the Corot light curve morphology agrees very well with the Spitzer IRAC-based classification of the systems. The percentage of AA Tau-like light curves decreases as the inner disk dissipates, from 40% +- 10% in systems with thick inner disks to 36% +- 16% in systems with anemic disks and none in naked photosphere systems. Indeed, 91% +- 29% of the CTTS with naked photospheres exhibit pure spot-like variability, while only 18% +- 7% of the thick disk systems do so, presumably those seen at low inclination and thus free of variable obscuration. AA Tau-like light curves are found to be fairly common, with a frequency of at least ~ 30 to 40% in young stars with inner dusty disks. The temporal evolution of the light curves indicates that the structure of the inner disk warp, located close to the corotation radius and responsible for the obscuration episodes, varies over a timescale of a few (~ 1-3) rotational periods. This probably reflects the highly dynamical nature of the star-disk magnetospheric interaction.
Highlights
T Tauri stars are young, optically visible, low-mass stars still contracting toward the main sequence
We search for possible light curve variability of the same nature as that observed in the classical T Tauri star AA Tau, which was attributed to a magnetically controlled inner disk warp
91% ± 29% of the classical T Tauri stars (CTTSs) with naked photospheres exhibit pure spot-like variability, while only 18% ± 7% of the thick disk systems do so, presumably those seen at low inclination and free of variable obscuration
Summary
T Tauri stars are young, optically visible, low-mass stars still contracting toward the main sequence. Part of the ionized material in the inner disk region is ejected by a magnetically controlled wind In this scenario, the broad permitted emission lines are formed partly in the accretion funnel and the hot spot emits a continuum flux that is responsible for the UV and optical excess that veils the photospheric lines. Because of the differential rotation between the star and the inner disk region, the magnetic field lines become distorted after a few rotational periods and eventually reconnect, restoring the initial field configuration. This process continues while the star rotates. The complete rotation analysis will be discussed separately in another paper (Affer et al, in prep.)
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