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Issue A&A
Volume 467, Number 1, May III 2007
Page(s) L23 - L27
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20077304



A&A 467, L23-L27 (2007)
DOI: 10.1051/0004-6361:20077304

Letter

A very massive runaway star from Cygnus OB2

F. Comerón1 and A. Pasquali2

1  ESO, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
    e-mail: fcomeron@eso.org
2  Max-Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
    e-mail: pasquali@mpia.de

(Received 15 February 2007 / Accepted 3 April 2007)

Abstract
Aims.We investigate the star BD+43° 3654 and the possibility that it may have originated in the massive OB association Cygnus OB2.
Methods.We present new spectroscopic observations allowing a reliable spectral classification of the star, and discuss existing MSX observations of its associated bow shock and astrometric information not previously studied.
Results.Our observations reveal that BD+43° 3654 is a very early and luminous star of spectral type O4If, with an estimated mass of (70 $\pm$ 15) $M_\odot$ and an age of ~1.6 Myr. The high spatial resolution of the MSX observations allows us to determine its direction of motion in the plane of the sky by means of the symmetry axis of the well-defined bow shock, which matches well the orientation expected from the proper motion. Tracing back its path across the sky we find that BD+43° 3654 was located near the central, densest region of Cygnus OB2 at a time in the past similar to its estimated age.
Conclusions.BD+43° 3654 turns out to be one of the three most massive runaway stars known, and it most likely formed in the central region of Cygnus OB2. A runaway formation mechanism by means of dynamical ejection is consistent with our results.


Key words: stars: early-type -- stars: kinematics -- stars: individual: BD+43° 3654 -- Galaxy: open clusters and associations: individual: Cygnus OB2



© ESO 2007


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