A study of dust properties in the inner sub-au region of the Herbig Ae star HD 169142 with VLTI/PIONIER ^⋆

¹ Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, Konkoly Thege Miklós út 15-17, 1121 Budapest, Hungary
e-mail: lei.chen@csfk.mta.hu
² Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
³ University of Exeter, Department of Physics and Astronomy, Stocker Road, Exeter, Devon EX4 4QL, UK
⁴ Laboratoire Lagrange, Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Boulevard de l’Observatoire, CS 34229, 06304 Nice Cedex 4, France
⁵ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

Received: 23 July 2017
Accepted: 5 September 2017

Abstract

Context. An essential step to understanding protoplanetary evolution is the study of disks that contain gaps or inner holes. The pre-transitional disk around the Herbig star HD 169142 exhibits multi-gap disk structure, differentiated gas and dust distribution, planet candidates, and near-infrared fading in the past decades, which make it a valuable target for a case study of disk evolution.

Aims. Using near-infrared interferometric observations with VLTI/PIONIER, we aim to study the dust properties in the inner sub-au region of the disk in the years 2011−2013, when the object is already in its near-infrared faint state.

Methods. We first performed simple geometric modeling to characterize the size and shape of the NIR-emitting region. We then performed Monte-Carlo radiative transfer simulations on grids of models and compared the model predictions with the interferometric and photometric observations.

Results. We find that the observations are consistent with optically thin gray dust lying at R_in ~ 0.07 au, passively heated to T ~ 1500 K. Models with sub-micron optically thin dust are excluded because such dust will be heated to much higher temperatures at similar distance. The observations can also be reproduced with a model consisting of optically thick dust at R_in ~ 0.06 au, but this model is plausible only if refractory dust species enduring ~ 2400 K exist in the inner disk.