HD 95881: a gas rich to gas poor transition disk?^*

¹ Astronomical Institute “Anton Pannekoek”, University of Amsterdam, PO Box 94249, 1090 GE Amsterdam, The Netherlands e-mail: verhoeff@uva.nl
² Astronomical Institute Utrecht, University of Utrecht, PO Box 80000, 3508 TA Utrecht, The Netherlands
³ Institute for Astronomy, KU Leuven Celestijnenlaan 200B, 3001 Leuven, Belgium
⁴ Max Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁵ CEA/DSM/DAPNIA/Service d'Astrophysique, CE Saclay, 91191 Gif-sur-Yvette, France
⁶ Leiden Observatory, Niels Bohrweg 2, 2300 RA Leiden, The Netherlands
⁷ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
⁸ SRON Netherlands Institute for Space Research, PO Box 800, 9700 AV Groningen, The Netherlands

Received: 8 June 2009
Accepted: 30 March 2010

Abstract

Context. Based on the far infrared excess the Herbig class of stars is divided into a group with flaring circumstellar disks (group I) and a group with flat circumstellar disks (group II). Dust sedimentation is generally proposed as an evolution mechanism to transform flaring disks into flat disks. Theory predicts that during this process the disks preserve their gas content, however observations of group II Herbig Ae stars demonstrate a lack of gas.

Aims. We map the spatial distribution of the gas and dust around the group II Herbig Ae star HD 95881.

Methods. We analyze optical photometry, Q-band imaging, infrared spectroscopy, and K and N-band interferometric spectroscopy. We use a Monte Carlo radiative transfer code to create a model for the density and temperature structure which quite accurately reproduces all the observables.

Results. We derive a consistent picture in which the disk consists of a thick puffed up inner rim and an outer region which has a flaring gas surface and is relatively void of “visible” dust grains.

Conclusions. HD 95881 is in a transition phase from a gas rich flaring disk to a gas poor self-shadowed disk.