Herschel Hi-GAL imaging of massive young stellar objects

We used Herschel Hi-GAL (Herschel infrared Galactic Plane survey) data to determine whether massive young stellar objects (MYSOs) are resolved at 70 μm and to study their envelope density distribution. Our analysis of three relatively isolated sources in the l = 30° and 59° Galactic fields show that the objects are partially resolved at 70 μm. The Herschel Hi-GAL survey data have a high scan velocity which makes unresolved and partially resolved sources appear elongated in the 70 μm images. We analysed the two scan directions separately and examine the intensity profile perpendicular to the scan direction. Spherically symmetric radiative transfer models with a power-law density distribution were used to study the circumstellar matter distribution. Single dish submm data were also included to study how different spatial information affects the fitted density distribution. The density distribution which best fits both the 70 μm intensity profile and spectral energy distribution has an average index of ∼0.5. This index is shallower than expected and is probably due to the dust emission from bipolar outflow cavity walls not accounted for in the spherical models. We conclude that 2D axisymmetric models and Herschel images at low scan speeds are needed to better constrain the matter distribution around MYSOs

Multiwavelength modelling of the circumstellar environment of the massive protostar AFGL 2591 VLA 3

We have studied the dust density, temperature, and velocity distributions of the archetypal massive young stellar object (MYSO) AFGL 2591. Given its high luminosity (⁠L=2×10⁵L⊙⁠) and distance (d = 3.3 kpc), AFGL 2591 has one of the highest L−−√/d ratio, giving better resolved dust emission than any other MYSO. As such, this paper provides a template on how to use resolved multiwavelength data and radiative transfer to obtain a well-constrained 2D axisymmetric analytic rotating infall model. We show for the first time that the resolved dust continuum emission from Herschel 70- μm observations is extended along the outflow direction, whose origin is explained in part from warm dust in the outflow cavity walls. However, the model can only explain the kinematic features from CH3CN observations with unrealistically low stellar masses (<15 M⊙), indicating that additional physical processes may be playing a role in slowing down the envelope rotation. As part of our three-step continuum and line fitting, we have identified model parameters that can be further constrained by specific observations. High-resolution mm visibilities were fitted to obtain the disc mass (6 M⊙) and radius (2200 au). A combination of SED and near-infrared observations were used to estimate the luminosity and envelope mass together with the outflow cavity inclination and opening angles