Letter to the Editor

Herschel discovery of a new class of cold, faint debris discs^⋆

¹ Dpt. Física Teórica, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain
e-mail: carlos.eiroa@uam.es
² ESA-ESAC Gaia SOC, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
³ Astrophysikalisches Institut und Universitätssternwarte, Friedrich-Schiller-Universität, Schillergäßchen 2-3, 07745 Jena, Germany
⁴ Dpt. de Astrofísica, Centro de Astrobiología (INTA-CSIC), ESAC Campus, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
⁵ Institut d’Astrophysique et de Géophysique, Université de Liege, 17 Allée du Six Août, 4000 Sart Tilman, Belgium
⁶ NASA Herschel Science Center, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA
⁷ Université Joseph Fourier/CNRS, Laboratoire d’Astrophysique de Grenoble, UMR 5571, Grenoble, France
⁸ European Space Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago 19, Chile
⁹ NASA Goddard Space Flight Center, Exoplanets and Stellar Astrophysics, Code 667, Greenbelt, MD 20771, USA
¹⁰ UNINOVA-CA3, Campus da Caparica, Quinta da Torre, Monte de Caparica, 2825-149 Caparica, Portugal
¹¹ Christian-Albrechts-Universität zu Kiel, Institut für Theoretische Physik und Astrophysik, Leibnizstr. 15, 24098 Kiel, Germany
¹² ESA Astrophysics & Fundamental Physics Missions Division, ESTEC/SRE-SA, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
¹³ INSA at ESAC, 28691 Villanueva de la Cañada, Madrid, Spain
¹⁴ Onsala Space Observatory, Chalmers University of Technology, 439 92 Onsala, Sweden
¹⁵ Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Dpt. Astrofísica, Av. Complutense s/n, 28040 Madrid, Spain
¹⁶ Jet Propulsion Laboratory, California Institute of Technology, MS 183-900, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
¹⁷ LESIA, Observatoire de Paris, 92195 Meudon France
¹⁸ Department of Physics and Astrophysics, Open University, Walton Hall, Milton Keynes MK7 6AA, UK
¹⁹ Rutherford Appleton Laboratory, Chilton OX11 0QX, UK

Received: 30 July 2011
Accepted: 19 October 2011

Abstract

We present Herschel PACS 100 and 160 μm observations of the solar-type stars α Men, HD 88230 and HD 210277, which form part of the FGK stars sample of the Herschel open time key programme (OTKP) DUNES (DUst around NEarby Stars). Our observations show small infrared excesses at 160 μm for all three stars. HD 210277 also shows a small excess at 100 μm, while the 100 μm fluxes of α Men and HD 88230 agree with the stellar photospheric predictions. We attribute these infrared excesses to a new class of cold, faint debris discs. Both α Men and HD 88230 are spatially resolved in the PACS 160 μm images, while HD 210277 is point-like at that wavelength. The projected linear sizes of the extended emission lie in the range from  ~115 to  ≤ 250 AU. The estimated black body temperatures from the 100 and 160 μm fluxes are  ≲22 K, and the fractional luminosity of the cold dust is L_dust/L _⋆  ~ 10^-6, close to the luminosity of the solar-system’s Kuiper belt. These debris discs are the coldest and faintest discs discovered so far around mature stars, so they cannot be explained easily invoking “classical” debris disc models.