Model infrared spectra of passively heated proto-planetary disks surrounding intermediate-mass pre-main-sequence stars

¹ Astronomical Institute, University of Amsterdam, Kruislaan 403, 1098 AJ Amsterdam, The Netherlands e-mail: waters@uva.nl
² Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
³ Astronomical Institute, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands
⁴ Max Planck Institut Für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁵ Department of Astrophysics/IMAPP, Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands

Received: 8 February 2008
Accepted: 9 January 2009

Abstract

Aims. We study theoretical spectra at mid-infrared (5-40 ) wavelengths of proto-planetary disks surrounding intermediate-mass pre-main-sequence stars. Observations show a wide range of spectral shapes and a rich variety in strength and shape of dust resonances. These strong variations in spectral shape reflect differences in the nature and spatial distribution of dust particles in the disk. The aim of this study is to establish what model parameters influence the mid-IR spectra of planet-forming disks.

Methods. A grid of models of passively heated proto-planetary disks is used to calculate the infrared spectrum. We use hydrostatic equilibrium disk models and radiative transfer to calculate the emerging spectrum. We focus on the effects that different disk geometries (flaring, self-shadowed) and dust mineralogy have on the emerging 5-40  spectrum. We adopt four scenarios for the radial and vertical distribution of crystalline silicate dust.

Results. In our model, the 23.5  forsterite band is more sensitive to emission from regions <30 AU, while the 33.5  forsterite band probes regions up to 50 AU. The 23.5  band strength does not depend on the degree of flaring of the disk, while the 33.5  band does. Only models with a substantial abundance (>5 percent) of crystalline silicates at a long distance from the star (>20-50 AU) show detectable emission in the 33.5  forsterite band. The carbon-dust abundance affects the strength of the dust resonances in the 10  spectral region, but not in the 30  region.