EDP Sciences
Free access
Issue
A&A
Volume 446, Number 3, February II 2006
Page(s) 1095 - 1105
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20053951
A&A 446, 1095-1105 (2006)
DOI: 10.1051/0004-6361:20053951

Multiwavelength monitoring of BD+53°2790 , the optical counterpart to 4U 2206+54

P. Blay1, I. Negueruela2, P. Reig3, 4, M. J. Coe5, R. H. D. Corbet6, 7, J. Fabregat8 and A. E. Tarasov9

1  Institut de Ciència dels Materials, Universidad de Valencia, PO Box 22085, 46071 Valencia, Spain
    e-mail: pere.blay@uv.es
2  Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal, EPSA, Universidad de Alicante, PO Box 99, 03080 Alicante, Spain
    e-mail: ignacio@dfists.ua.es
3  Foundation for Research and Technology-Hellas, 711 10 Heraklion, Crete, Greece
4  Physics Department, University of Crete, 710 03 Heraklion, Crete, Greece
    e-mail: pau@physics.uoc.gr
5  School of Physics and Astronomy, Southampton University, Southampton SO17 1BJ, UK
    e-mail: M.J.Coe@soton.ac.uk
6  X-ray Astrophysics Laboratory, Code 662, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA
7  Universities Space Research Association
    e-mail: corbet@milkyway.gsfc.nasa.gov
8  Observatori Astronómic, Universidad de Valencia, PO BOX 22085, 46071 Valencia, Spain
    e-mail: juan@pleione.oauv.uv.es
9  Crimean Astrophysical Observatory, Nauchny, Crimea, 334413, Ukraine
    e-mail: tarasov@crao.crimea.ua

(Received 29 July 2005 / Accepted 5 October 2005 )

Abstract
We present the results of our long-term monitoring of BD+53°2790 , the optical counterpart to the X-ray source 4U 2206+54. Unlike previous studies that classify the source as a Be/X-ray binary, we find that its optical and infrared properties differ from those of typical Be stars: the variability of the V/R ratio is not cyclical; there are variations in the shape and strength of the H$\alpha$ emission line on timescales less than 1 day; and no correlation between the EW and the IR magnitudes or colors is seen. Our observations suggest that BD+53°2790 is very likely a peculiar O9.5V star. In spite of exhaustive searches we cannot find any significant modulation in any emission line parameter or optical/infrared magnitudes. Spectroscopy of the source extending from the optical to the K-band confirms the peculiarity of the spectrum: not only are the He lines stronger than expected for an O9.5V star but also there is no clear pattern of variability. The possibility that BD+53°2790 is an early-type analogue to He-strong stars (like $\theta^1$ Ori C) is discussed.


Key words: stars: early-type -- stars: emission-line, Be -- stars: magnetic fields -- stars: individual: BD$+53\degr$2790

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