Letter to the Editor

δ Centauri: a new binary Be star detected by VLTI/AMBER spectro-interferometry^*

¹ Max Planck Intitut fur Radioastronomie, Auf dem Hugel 69, 53121 Bonn, Germany e-mail: meilland@mpifr-bonn.mpg.de
² Laboratoire A.H. FIZEAU, UMR 6525, UNS/OCA/CNRS, Campus Valrose, 06108 Nice Cedex 2, France
³ Laboratoire d'Astrophysique de Grenoble, UMR 5571 Université Joseph Fourier/CNRS, BP 53, 38041 Grenoble Cedex 9, France
⁴ INAF – Osservatorio Astrofisico di Arcetri, Istituto Nazionale di Astrofisica, Largo E. Fermi 5, 50125 Firenze, Italy

Received: 16 July 2008
Accepted: 29 July 2008

Abstract

Aims. We study the Be star δ Cen circumstellar disk using long-baseline interferometry which is the only observing technique capable of resolving spatially and spectroscopically objects smaller than 5 mas in the H and K band.

Methods. We used the VLTI/AMBER instrument on January 6, 8, and 9, 2008, in the H and K bands to complete low (35) and medium (1500) spectral resolution observations.

Results. We detected an oscillation in the visibility curve plotted as a function of the spatial frequency which is a clear signature of a companion around δ Cen. Our best-fit soltution infers a binary separation of 68.7 mas, a companion flux contribution in the K band of about 7% of the total flux, a PA of 117.5°, and an envelope flux around the Be primary that contributes up to about 50% of the total flux, in agreement with our Spectral Energy Distribution (SED) fit. The envelope size is estimated to be 1.6 mas in K but no departure from spherical symmetry is detected.