An infrared image of the dust disc around ss Pic

Abstract

The star β Pictoris is a normal main-sequence star with a remnant disc of cool dust around it. We present observations of the β Pic dust disc in the far-infrared, obtained using the photometer (ISOPHOT) on the Infrared Space Observatory (ISO) satellite. We resolve the edge-on disc using high-resolution scans, with full widths at half-maximum of 8.7 × 2.9 arcsec2 (± 1.5 arcsec) at 25 μ m (corresponding to a characteristic disc radius of 84 au) and 14.5 × 6.1 arcsec2 (± 2.0 arcsec) at 60 μ m (corresponding to 140 au). The disc is just resolved in the minor axis direction at 60 μ m. Photometry, from 4.85 to 200 μ m, is combined with low-resolution spectroscopy and modelled to give an average dust temperature of 85 K, using a blackbody modified by an emissivity proportional to λ-1. A simple radiative transfer model is also used, with the grain radius ranging from 1 μ m to 5 mm. The dust mass is estimated to be around (3–10) × 10-8 M⊙ (0.9–2.7 Mmoon), depending on the selected grain parameters.