Low abundance, strong features: window-dressing crystalline forsterite in the disk wall of HD 100546⋆
Astronomical Institute “Anton Pannekoek”, University of
Amsterdam, PO Box
94249, 1090 GE
2 SRON Netherlands Institute for Space Research, PO Box 800, 9700 AV, Groningen, The Netherlands
3 SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
4 Instituut voor Sterrenkunde, K.U. Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
5 Department of Astrophysics/IMAPP, Radboud University Nijmegen, PO Box 9010 6500 GL Nijmegen, The Netherlands
6 Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
7 Astronomical Institute Utrecht, University of Utrecht, PO Box 80000, 3508 TA Utrecht, The Netherlands
8 UJF – Grenoble 1 / CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, Grenoble 38041, France
9 The University of Texas at Austin, Department of Astronomy, 1 University Station C1400, Austin, Texas 78712-0259, USA
10 Dpt. de Física Teórica, Fac. de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain
Received: 22 February 2011
Accepted: 19 May 2011
Context. Forsterite is one of the crystalline dust species that is often observed in protoplanetary disks and solar system comets. Being absent in the interstellar medium, it must be produced during the disk lifetime. It can therefore serve as a tracer of dust processing and disk evolution, which can lead to a better understanding of the physical processes occurring in the disk, and possibly planet formation. However, the connection of these processes with the overall disk crystallinity remains unclear.
Aims. We aim to characterize the forsterite abundance and spatial distribution in the disk of the Herbig Be star HD 100546, to investigate if a connection exists with the large disk gap.
Methods. We use a 2D radiative transfer code, MCMax, to model the circumstellar dust around HD 100546. We use VISIR Q-band imaging to probe the outer disk geometry and mid-infrared features to model the spatial distribution of forsterite. The temperature-dependent shape of the 69 μm feature observed with Herschel⋆⋆⋆/PACS is used as a critical tool to constrain this distribution.
Results. We find a crystalline mass fraction of 40–60%, located close to the disk wall between 13 and 20 AU, and possibly farther out at the disk surface. The forsterite is in thermal contact with the other dust species. We put an upper limit on the iron content of forsterite of 0.3%.
Conclusions. Optical depth effects play a key role in explaining the observed forsterite features, hiding warm forsterite from view at short wavelengths. The disk wall acts as a showcase: it displays a localized high abundance of forsterite, which gives rise to a high observed crystallinity, while the overall mass fraction of forsterite is a factor of ten lower.
Key words: stars: individual: HD 100546 / stars: pre-main sequence / protoplanetary disks / radiative transfer
Appendices A–C are available in electronic form at http://www.aanda.org
© ESO, 2011