Very deep images of the innermost regions of theβPictoris debris disc atL′

Abstract

Context. Very few debris discs have been imaged in scattered light at wavelengths beyond 3 μm because the thermal emission from both the sky and the telescope is generally too strong with respect to the faint emission of a debris disc. We present here the first analysis of a high angular resolution image of the disc of β Pictoris at 3.8 μm. Aims. Our primary objective is to probe the innermost parts of the β Pictoris debris disc and describe its morphology. We performed extensive forward modelling to correct for the biases induced by angular differential imaging on extended objects and derive the physical parameters of the disc. Methods. This work relies on a new analysis of seven archival data sets of β Pictoris observed with the NaCo instrument at the Very Large Telescope in the L band, including observations made with the Annular Groove Phase Mask vortex coronagraph in 2013. The data analysis consists of angular differential imaging associated with disc forward modelling to correct for the biases induced by that technique. The disc model is subtracted from the data and the reduction performed again in order to minimize the residuals in the final image.Results. The disc is detected above a 5σ level between 0.4 and 3.8 . The two extensions have a similar brightness within error bars. We confirm an asymmetry previously observed at larger distances from the star and at shorter wavelengths: the isophotes are more widely spaced on the north-west side (above the disc apparent midplane) than on the south-east side. This is interpreted as a small inclination of the disc combined with anisotropic scattering. Our best-fit model has an inclination of 86 • with an anisotropic HenyeyGreenstein coefficient of 0.36. This interpretation is supported by a new asymmetry detected in the disc: the disc is significantly bowed towards the north-west within 3 (above the apparent midplane). We also detect a possible new asymmetry within 1 , but at this stage we cannot discern between a real feature and an underlying speckle.

Signatures of massive collisions in debris discs

“…As a result, these regions should experience both more frequent and more violent (i.e., destructive) impacts. This 6 AU distance also roughly corresponds to the best resolution obtained on resolved images of debris discs (see, for example, Milli et al 2014, for the archetypal β Pictoris system). Last but not least, 6 AU is also the location where a high level of dustiness has been observed around HD 172555, one of the best known systems with high-luminosity excesses (Lisse et al 2009;Johnson et al 2012).…”

The Mass of Stirring Bodies in the AU Mic Debris Disk Inferred from Resolved Vertical Structure

“…Previous studies of the scale height of debris disks have demonstrated a degeneracy between vertical structure, radial structure, and viewing geometry (e.g. Milli et al 2014). For example, it can be difficult to distinguish a disk that is vertically thin but slightly inclined from one that is vertically broad but perfectly edge-on.…”

New constraints on the dust surrounding HR 4796A

“…In that case, the Henyey-Greenstein g coefficient is an additional free parameter that can be used to quantify the anisotropy of scattering. Because the star subtraction is performed using ADI, the disc can be significantly self-subtracted (Milli et al 2012), and we implement the forward-modelling technique already described in Milli et al (2014) for β Pictoris to retrieve the best disc parameters. The results are shown in Table 2.…”