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Astron. Astrophys. 334, 873-894 (1998)


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Optical and X-ray monitoring, Doppler imaging, and space motion of the young star Par 1724 in Orion * ** ***

R. Neuhäuser 1, S.J. Wolk 2, G. Torres 2, Th. Preibisch 3, N.M. Stout-Batalha **** 4, A.P. Hatzes 5, S. Frink 6, R. Wichmann 7, E. Covino 8, J.M. Alcalá 8, W. Brandner 9, F.M. Walter 10, M.F. Sterzik 1 and R. Köhler 11

1 Max-Planck-Institut für Extraterrestrische Physik, D-85740 Garching, Germany (rne@mpe.mpg.de)
2 Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
3 Astronomisches Institut, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
4 Lick Observatory, University of California, Santa Cruz, CA 95064, USA
5 Astronomy Department, University of Texas, Austin, TX 78712, USA
6 Astronomisches Rechen-Institut Heidelberg, Mönchhofstraße 12-14, D-69120 Heidelberg, Germany
7 IUCAA, Post Bag 4, Ganeshkhind, Pune 411007, India
8 Osservatorio Astronomico di Capodimonte, I-80131 Napoli, Italy
9 Caltech - JPL/IPAC, Mail Code 100-22, Pasadena, CA 91125, USA
10 Department of Physics and Astronomy, SUNY, Stony Brook, NY 11794-3800, USA
11 Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany

Received 8 December 1997 / Accepted 23 February 1998

Abstract

We present a detailed study of the young T Tauri star Par 1724, located 15 arc min north of the Trapezium cluster in Orion. Our extensive VRI photometric measurements confirm the rotational period to be 5.7 days. Repeated high-resolution spectra show variability in the radial velocity with the same period. 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, which is responsible for most or all of the observed variability. Our high-resolution spectra yield a rotational velocity of [FORMULA], a surface gravity of [FORMULA], and a mean heliocentric radial velocity of [FORMULA], the latter being consistent with membership to the Orion association. The equivalent width of the lithium 6708Å line is variable, consistent with rotational modulation. The line is stronger when the spot is on the front side; the lithium abundance observed when the spot is on the back side is consistent 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 spatial resolution reveals no physically bound visual companions down to [FORMULA] arc sec separations and a magnitude difference up to [FORMULA] mag, and also no companion down to [FORMULA] arc sec with [FORMULA] mag. We also present the spectral energy distribution of Par 1724 and show that it does not display infrared excess. We estimate the bolometric luminosity to be [FORMULA], the spectral type to be K0, and the radius to be [FORMULA]. Although Par 1724 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 [FORMULA] years, with a mass of [FORMULA]. According to its present location and 3D space motion ([FORMULA] to the north relative to the cluster), Par 1724 may have been ejected from the Trapezium [FORMULA] yrs ago. We cannot rule out that a close companion is responsible for part of the radial velocity variation, but such a close pair might still have been ejected together depending on the encounter dynamics. Par 1724 appears to be a very young, weak-line run-away T Tauri star moving north relative to the Trapezium, but sharing the Orion radial velocity.

Key words: stars: activity – stars: formation – stars: kinematics – stars: pre-main sequence – stars: individual: Par 1724

* Partly based on observations with the Multiple Mirror Telescope, a joint facility of the Smithsonian Institution and the University of Arizona; the 2.1m telescope at McDonald Observatory; the European Southern Observatory 3.6m, 1.52m, and 0.91m telescopes under programs 57.E-0250, 57.E-0646, and 56.E-0601; the Calar Alto Observatory 3.5m, 2.2m, and 1.2m telescopes; and the Cerro Tololo Inter-American and Kitt Peak National Observatories, NOAO, which are operated by the Association of Universities for Research in Astronomy, under contract with the National Science Foundation.
** Figs. 2, 7, and 10 are available by ftp from CDS.
*** Figs. 2, 7, and 10 are only available in the online-version of this paper
**** Now at: Dep. Astrofisica, Obs. National, Rio de Janeiro, Brasil

Send offprint requests to: Ralph Neuhäuser

© European Southern Observatory (ESO) 1998

Online publication: June 2, 1998

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