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

Abstract

Context. An essential step to understanding protoplanetary evolution is the study of disks that contain gaps or inner holes. The pretransitional 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.

Tiny grains shining bright in the gaps of Herbig Ae transitional discs

“…Our rings are at a similar location to the ∼ 100 mas (∼ 11 AU) ring and asymmetry found by Ligi et al (2018). The location of our inner disc (r d ) is at 0.11 AU (0.96 mas), which is slightly beyond the radius of 0.07 AU found by Chen et al (2018) from their modelling of the inner disc.…”

Variable Warm Dust around the Herbig Ae Star HD 169142: Birth of a Ring?*

“…The uncertainties of the parameters are estimated with the bootstrapping method. The best-fit model parameters for the 2011-2013 observations (Chen et al 2018 observations could be due to a simultaneous slight fading of the innermost ring, but could also be related to observational uncertainty.…”

“…The model reproduces the observations within the formal uncertainties, accounting for the steep drop of visibility at the short baselines with the outer ring at ∼0.3 au. For comparison, our previous model of the 2011-2013VLTI/PIONIER observations (model 2012-2013Chen et al 2018) is also listed.…”

“…Wagner et al (2015) revealed a fading trend in the NIR, indicating that the inner warm dust has lost half of its fractional luminosity in no more than 10 years. With NIR interferometry, we constrained the location and grain size distribution of the dust (Chen et al 2018), finding it most likely to be optically thin dust located at ∼0.08 au from the central star, consisting of mainly large dust grains (>1 µm). We further speculated that the dust might consist of second-generation grains released by collisional cascades following collisional events between planetesimals.…”

“…H-band Visibilities from the VLTI/PIONIER observations of HD 169142 in 2018 and 2019, and our starring-ring-halo model fitting. Earlier VLTI observations from 2011-2013 and our previous model(Chen et al 2018) are plotted for comparison.…”