EDP Sciences
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Volume 475, Number 1, November III 2007
Page(s) 243 - 250
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:20077625

A&A 475, 243-250 (2007)
DOI: 10.1051/0004-6361:20077625

A near-infrared interferometric survey of debris disk stars

I. Probing the hot dust content around $\epsilon$ Eridani and $\tau$ Ceti with CHARA/FLUOR
E. Di Folco1, O. Absil2, 3, J.-C. Augereau2, A. Mérand4, V. Coudé du Foresto5, F. Thévenin6, D. Defrère3, P. Kervella5, T. A. ten Brummelaar4, H. A. McAlister4, S. T. Ridgway7, 4, J. Sturmann4, L. Sturmann4, and N. H. Turner4

1  Observatoire de Genève, Université de Genève, Chemin des Maillettes 51, 1290 Sauverny, Switzerland
    e-mail: emmanuel.difolco@obs.unige.ch
2  Laboratoire d'Astrophysique de l'Observatoire de Grenoble, UMR CNRS/UJF 5571, BP 53, 38041 Grenoble Cedex 9, France
3  Institut d'Astrophysique et de Géophysique, Université de Liège, 17 Allée du Six Août, 4000 Liège, Belgium
4  Center for High Angular Resolution Astronomy, Georgia State University, PO Box 3969, Atlanta, Georgia 30302-3965, USA
5  LESIA, UMR8109, Observatoire de Paris-Meudon, 5 place J. Janssen, 92195 Meudon, France
6  Laboratoire Cassiopée, CNRS, Observatoire de la Côte d'Azur, BP 4229, 06304 Nice Cedex 4, France
7  National Optical Astronomical Observatory, 950 North Cherry Avenue, Tucson, AZ 85719, USA

(Received 10 April 2007 / Accepted 30 July 2007)

Context.The quest for hot dust in the central region of debris disks requires high resolution and high dynamic range imaging. Near-infrared interferometry is a powerful means to directly detect faint emission from hot grains.
Aims.We probed the first 3 AU around $\tau$ Ceti and $\epsilon$ Eridani with the CHARA array (Mt Wilson, USA) in order to gauge the 2 $\mu$m excess flux emanating from possible hot dust grains in the debris disks and to also resolve the stellar photospheres.
Methods.High precision visibility amplitude measurements were performed with the FLUOR single mode fiber instrument and telescope pairs on baselines ranging from 22 to 241 m of projected length. The short baseline observations allow us to disentangle the contribution of an extended structure from the photospheric emission, while the long baselines constrain the stellar diameter.
Results.We have detected a resolved emission around $\tau$ Cet, corresponding to a spatially integrated, fractional excess flux of $0.98\pm0.21 \times 10^{-2}$ with respect to the photospheric flux in the $K^{\prime}$-band. Around $\epsilon$ Eri, our measurements can exclude a fractional excess of greater than $0.6\times 10^{-2}$ ($3\sigma$). We interpret the photometric excess around $\tau$ Cet as a possible signature of hot grains in the inner debris disk and demonstrate that a faint, physical or background, companion can be safely excluded. In addition, we measured both stellar angular diameters with an unprecedented accuracy: $\Theta_{\rm LD}(\tau\,{\rm Cet})= 2.015 \pm 0.011$ mas and $\Theta_{\rm LD}(\epsilon\,{\rm Eri})=2.126 \pm 0.014$ mas.

Key words: stars: individual: $\tau$ Cet & $\epsilon$ Eri -- stars: fundamental parameters -- circumstellar matter -- methods: observational -- techniques: interferometric

© ESO 2007