  Context. HD 172555 is a young A7 star belonging to the Beta 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 (SED) 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 microns 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 microns). We derive a large dust particle mass of 4.8e-4 Earth
masses and an atomic oxygen mass of 2.5e-2*R^2 Earth masses, 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.
