HD 172555: detection of 63 μm [OI] emission in a debris disc^⋆,⋆⋆

¹ Centro de Astrobiología – Depto. Astrofísica (CSIC–INTA), ESAC Campus, PO Box 78, 28691 Villanueva de la Cañada, Spain
e-mail: riviere@cab.inta-csic.es
² Calar Alto Observatory, Centro Astronómico Hispano-Alemán C/Jesús Durbán Remón, 2-2, 04004 Almería, Spain
³ UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique (IPAG) UMR 5274, 38041 Grenoble, France
⁴ Exoplanets and Stellar Astrophysics Lab, NASA Goddard Space Flight Center, Code 667, Greenbelt, MD, 20771, USA
⁵ Dep. de Física Teórica, Fac. de Ciencias, UAM Campus Cantoblanco, 28049 Madrid, Spain
⁶ SOFIA-USRA, NASA Ames Research Center, MS N211-3, Moffett Field, CA 94035, USA
⁷ Astronomy Department, University of California, Berkeley CA 94720-3411, USA
⁸ ALMA, Avda Apoquindo 3846, Piso 19, Edificio Alsacia, Las Condes, Santiago, Chile
⁹ Laboratorio Franco-Chileno de Astronomia (UMI 3386: CNRS – U de Chile / PUC / U Conception), Santiago, Chile

Received: 4 June 2012
Accepted: 27 September 2012

Abstract

Context.HD 172555 is a young A7 star belonging to the β Pictoris moving group that harbours a debris disc. The Spitzer/IRS spectrum of the source showed mid-IR features such as silicates and glassy silica species, indicating the presence of a warm dust component with small grains, which places HD 172555 among the small group of debris discs with such properties. The IRS spectrum also shows a possible emission of SiO gas.

Aims. We aim to study the dust distribution in the circumstellar disc of HD 172555 and to asses the presence of gas in the debris disc.

Methods. As part of the GASPS open time key programme, we obtained Herschel/PACS photometric and spectroscopic observations of the source. We analysed PACS observations of HD 172555 and modelled the spectral energy distribution with a modified blackbody and the gas emission with a two-level population model with no collisional de-excitation.

Results. We report for the first time the detection of [OI] atomic gas emission at 63.18 μm in the HD 172555 circumstellar disc. We detect excesses due to circumstellar dust toward HD 172555 in the three photometric bands of PACS (70, 100, and 160 μm). We derive a large dust particle mass of (4.8 ± 0.6) × 10^-4 M_⊕ and an atomic oxygen mass of 2.5 × 10^-2R² M_⊕, where R in AU is the separation between the star and the inner disc. Thus, most of the detected mass of the disc is in the gaseous phase.