Dust shell model of the water fountain source IRAS 16342–3814

Abstract

Aims. We investigate the circumstellar dust shell of the water fountain source IRAS 16342-3814. Methods. We performed two-dimensional radiative transfer modeling of the dust shell, taking into account previously observed spectral energy distributions (SEDs) and our new J-band imaging and H-and K S -band imaging polarimetry obtained using the VLT/NACO instrument. Results. Previous observations expect an optically thick torus in the equatorial plane because of a striking bipolar appearance and a large viewing angle of 30−40 • . However, models with such a torus as well as a bipolar lobe and an AGB shell cannot fit the SED and the images simultaneously. We find that an additional optically and geometrically thick disk located inside a massive torus solves this problem. The masses of the disk and the torus are estimated to be 0.01 M at the a max = 100 μm dust and 1 M at a max = 10 μm dust, respectively. Conclusions. We discuss a possible formation scenario for the disk and torus based on a similar mechanism to the equatorial back flow. IRAS 16342-3814 is expected to undergo mass loss at a high rate. The radiation from the central star is shielded by the dust that was ejected in the subsequent mass loss event. As a result, the radiation pressure on dust particles cannot govern the motion of the particles anymore. The mass loss flow can be concentrated in the equatorial plane by help of an interaction, which might be the gravitational attraction by the companion, if it exists in IRAS 16342-3814. A fraction of the ejecta is captured in a circum-companion or circum-binary disk and the remains are escaping from the central star(s) and form the massive torus.

ALMA Observations of the Water Fountain Pre-planetary Nebula IRAS 16342-3814: High-velocity Bipolar Jets and an Expanding Torus

“…Both these flux densities are significantly in excess of the values (~ 113 & 30 mJy at 0.886 & 1.3 mm) derived from an extrapolation of the 2-D dust radiative-transfer model fit to IRAS 16342’s SED and near-IR polarised light imaging (Fig. 1 of Murakawa & Izumiura 2012), in which the dominant mass component is a 1 M ⊙ torus of radius 700 − 1000 AU that includes grains with a radius up to 10 μ m.…”

Investigation of dust properties of the proto-planetary nebula IRAS 18276−1431

“…In bipolar PPNs such as I18276, it is expected that the CDS has an optically thick dust torus/disc in the equatorial region and an envelope, which characterises the lobe shape. In our separate paper on the bipolar PPN IRAS 16342-3814, we needed an additional optically thick, geometrically thin disc inside the torus (Murakawa & Izumiura 2012). For I18276, we tried both model geometries, but found that the inner disc is not necessary.…”

“…The H and KS band data were taken with the Wollaston prism to measure the polarisation. The data were reduced following the same method as before (Murakawa & Izumiura 2012). Standard star data were used to calibrate the surface brightness and the polarisation, and also served to estimate the size of the point spread function (PSF).…”

Maser and Infrared Studies of Oxygen-Rich Late/Post-Asymptotic Giant Branch Stars and Water Fountains: Development of a New Identification Method

“…However, here we have a stronger correlation between the PPNe and the black body curve. This is presumably due to the fact that the far-infrared colours are more sensitive to the temperature of the cold dust component, which contributes most of the flux from the SEDs of PPNe (e.g., IRAS 16342−3814,Murakawa & Izumiura 2012). There are some objects, which deviate from the black body curve, that occupy the…”