Prospecting for planets in circumstellar dust: sifting the evidence from β Pictoris

Abstract

Spectroscopic evidence for an extended gaseous shell around the A5V star β Pictoris has been available for more than a decade1–5. Recently, the presence of a vast circumstellar cloud of particles was deduced from Infrared Astronomy Satellite (IRAS) measurements of excess thermal flux6–8. This interpretation is supported by a near-infrared (0.89 µm) coronagraphic image of the region beyond 100 AU from β Pic, which shows scattered starlight in a configuration consistent with a disk viewed nearly edge-on9. Conceivably, the β Pic system may represent one phase of planetary evolution. From an analysis of visible photometry and their coronagraph data, Smith and Terrile9 suggested that planetary accretion has swept out an extensive (∼30 AU) clearing at the centre of the disk. We report here a new analysis of the same data and the results of including the IRAS observations in the analysis. The consequent models do not produce a large inner clearing and suggest alternatively that significant particle number densities occur within several AU of the star. An illustrative case is used to evaluate the short-wavelength detectibility of circumstellar disks in less favourable orientations than that surrounding β Pic.