Letter to the Editor

Resolving the cold debris disc around a planet-hosting star ^*

PACS photometric imaging observations of q¹ Eridani (HD 10647, HR 506)

¹ Onsala Space Observatory, Chalmers University of Technology, 439 92 Onsala, Sweden e-mail: rene.liseau@chalmers.se
² Departamento de Física Teórica, C-XI, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain
³ Max Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁴ Johns Hopkins University Dept. of Physics and Astronomy, 3701 San Martin drive Baltimore, MD 21210 USA
⁵ Université Joseph Fourier/CNRS, Laboratoire d'Astrophysique de Grenoble, UMR 5571, Grenoble, France
⁶ Stockholm Observatory, AlbaNova University Center, Roslagstulls-backen 21, 106 91 Stockholm, Sweden
⁷ INSA at ESAC, 28691 Villanueva de la Cañada, Madrid, Spain
⁸ LAEX-CAB, Depto. Astrofísica, Centro de Astrobiología (INTA-CSIC), PO Box 78, 28691 Villanueva de la Cañada, Spain
⁹ ESA-ESAC Gaia SOC. PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
¹⁰ Institut d'Astrophysique et de Géophysique, Université de Liège, 17 Allée du Six Août, 4000 Sart Tilman, Belgium
¹¹ Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125, USA
¹² Centro Astronómico Hispano Alemán de Calar Alto (CAHA), C/ Jesús Durbán Remoń 2-2 04004 Almería, Spain

¹³ European Southern Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile
¹⁴ NASA Exoplanet Science Institute, California Institute of Technology, Pasadena, CA 91125, USA
¹⁵ Jet Propulsion Lab, California Institute of Technology, 4800 Oak Grove Dr, Pasadena, CA 91109, USA
¹⁶ NASA Goddard Space Flight Center, Exoplanets and Stellar Astrophysics, Code 667, Greenbelt, MD 20771, USA
¹⁷ UNINOVA-CA3, Campus da Caparica, Quinta da Torre, Monte de Caparica, 2825-149 Caparica, Portugal
¹⁸ University of Kiel, Institute of Theoretical Physics and Astrophysics, Leibnizstrasse 15, 24098 Kiel, Germany
¹⁹ ESA Astrophysics & Fund Physics Missions Division, ESTEC/SRE-SA, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
²⁰ Astrophysikalisches Institut und Universitätssternwarte, Friedrich-Schiller-Universität, Schillergäßchen 2-3, 07745 Jena, Germany
²¹ Department of Physics and Astronomy, Open University, Walton Hall, Milton Keynes MK7 6AA, UK
²² ESA/ESTEC Space Environment and Effects Section, PO Box 299, 2200 AG Noordwijk, The Netherlands
²³ LESIA, Observatoire de Paris, 92195, Meudon, France
²⁴ Science and Technology Facilities Council, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, UK

Received: 31 March 2010
Accepted: 16 April 2010

Abstract

Context. About two dozen exo-solar debris systems have been spatially resolved. These debris discs commonly display a variety of structural features such as clumps, rings, belts, excentric distributions and spiral patterns. In most cases, these features are believed to be formed, shaped and maintained by the dynamical influence of planets orbiting the host stars. In very few cases has the presence of the dynamically important planet(s) been inferred from direct observation.

Aims. The solar-type star q¹ Eri is known to be surrounded by debris, extended on scales of 30”. The star is also known to host at least one planet, albeit on an orbit far too small to make it responsible for structures at distances of tens to hundreds of AU. The aim of the present investigation is twofold: to determine the optical and material properties of the debris and to infer the spatial distribution of the dust, which may hint at the presence of additional planets.

Methods. The Photodetector Array Camera and Spectrometer (PACS) aboard the Herschel Space Observatory allows imaging observations in the far infrared at unprecedented resolution, i.e. at better than 6” to 12” over the wavelength range of 60 μm to 210 μm. Together with the results from ground-based observations, these spatially resolved data can be modelled to determine the nature of the debris and its evolution more reliably than what would be possible from unresolved data alone.

Results. For the first time has the q¹ Eri disc been resolved at far infrared wavelengths. The PACS observations at 70 μm, 100 μm and 160 μm reveal an oval image showing a disc-like structure in all bands, the size of which increases with wavelength. Assuming a circular shape yields the inclination of its equatorial plane with respect to that of the sky, i > 53°. The results of image de-convolution indicate that i likely is larger than 63°, where 90° corresponds to an edge-on disc.

Conclusions. The observed emission is thermal and optically thin. The resolved data are consistent with debris at temperatures below 30 K at radii larger than 120 AU. From image de-convolution, we find that q¹ Eri is surrounded by an about 40 AU wide ring at the radial distance of ~85 AU. This is the first real Edgeworth-Kuiper Belt analogue ever observed.