Optical and X-ray monitoring, Doppler imaging
and space motion of the young star Par 1724 in Orion
R. Neuhäuser, S.J. Wolk, G. Torres, Th. Preibisch, N.M. Stout-Batalha,
A.P. Hatzes, S. Frink, R. Wichmann, E. Covino, J.M. Alcala, W. Brandner,
F.M. Walter, M.F. Sterzik, and R. Köhler
Astronomy & Astrophysics, 334, 873, (1998)
We present a detailed study of the young T Tauri star P1724, located
15' north of the Trapezium cluster in Orion.
Our extensive photometric measurements in the V, R and I bands confirm
the rotational period to be approximately 5.7 days.
Repeated high-resolution spectra show low amplitude variability
in the radial velocity of the star.
A Doppler-imaging analysis based on high-S/N high-resolution spectra
yields an image showing a pronounced dark feature (spot) at relatively
low latitude. From its size and temperature
we conclude that it is responsible for the observed
photometric and spectroscopic variability.
Our high-resolution spectra yield a rotational
velocity v sin i ~ 71 km/s and a mean radial
velocity of ~ +23 km/s.
R band imaging reveals no visual companions down to separations
of 1 arc second and magnitude differences of up to Delta R = 7 mag.
We also collected UBVRIJHK photometry of the star and present its
spectral energy distribution, showing that P1724 is a naked T Tauri
We estimate the bolometric luminosity to be ~ 51 L_sun,
the spectral type to be K0, and the radius to be ~ 9 R_sun.
We obtain similar values of the radius from the Boltzmann law and the
Barnes-Evans relation. Also, the surface gravity derived from
Stromgren photometry, and independently from the location of the
the H-R diagram are in agreement with our direct measurement from h
This strongly supports a distance for P1724 consistent with ~ 460 pc.
Although P1724 appears to have lost all its circumstellar material,
its bolometric luminosity places it very close to the stellar
birth-line at an age of only ~ 2 10^5 years,
with a mass of ~ 3 M_sun.
The age from the H-R diagram is consistent with its present location
and 3D space motion (~ +20 km/s to the north relative to the
Trapezium) under the assumption that it was ejected from the Trapezium
~ 2 10^5 yrs ago.
P1724 thus appears to be a single, very young, naked,
weak-line T Tauri star moving north relative to the
Trapezium, but sharing the Orion radial velocity.
All our observations are consistent with P1724 being
a run-away T Tauri star, ejected from its birth place,
the Trapezium cluster, ~ 2 10^5 years ago.
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