OPTICAL AND X-RAY MONITORING, DOPPLER IMAGING, AND SPACE MOTION OF THE YOUNG STAR PAR-1724 IN ORION

We present a detailed study of the young T Tauri star Par 1724, locate d 15 are min north of the Trapezium cluster in Orion. Our extensive VR I photometric measurements confirm the rotational period to be 5.7 day s. Repeated high-resolution spectra show variability in the radial vel ocity with the same period. A Doppler imaging analysis based on high-S /N high-resolution spectra yields an image showing a pronounced dark f eature (spot) at relatively low latitude, which is responsible for mos t or all of the observed variability. Our high-resolution spectra yiel d a rotational velocity of v.sin i similar or equal to 71 km s(-1), a surface gravity of log g similar or equal to 3, and a mean heliocentri c radial velocity of similar to 23 km s(-1), the latter being consiste nt with membership to the Orion association. The equivalent width of t he lithium 6708 Angstrom line is variable, consistent with rotational modulation. The line is stronger when the spot is on the front side; t he lithium abundance observed when the spot is on the back side is con sistent with the primordial value. Many ROSAT X-ray observations show that Par 1724 is a strong and variable X-ray source. It has shown one of the most powerful X-ray flares. Our deep infrared imaging at high s patial resolution reveals no physically bound visual companions down t o similar to 1 are sec separations and a magnitude difference up to De lta R = 7 mag, and also no companion down to similar to 0.13 arc sec w ith Delta K = 2.5 mag. We also present the spectral energy distributio n of Par 1724 and show that it does not display infrared excess. We es timate the bolometric luminosity to be similar to 49 L., the spectral type to be K0, and the radius to be similar to 9 R.. Although Par 1724 appears to have lost all its circumstellar material, its bolometric l uminosity places it very close to the stellar birth-line at an age of only similar to 2.10(5) years, with a mass of similar to 3 M.. Accordi ng to its present location and 3D space motion (similar to 20 km s(-1) to the north relative to the cluster), Par 1724 may have been ejected from the Trapezium similar to 10(5) yrs ago. We cannot rule out that a close companion is responsible for part of the radial velocity varia tion, but such a close pair might still have been ejected together dep ending on the encounter dynamics. Par 1724 appears to be a very young, weak-line run-away T Tauri star moving north relative to the Trapeziu m, but sharing the Orion radial velocity.