| Description |
Herbig Be stars are the link between massive protostars and the intermediate-mass Herbig Ae stars. While for this last group the disc has been characterised in terms of flaring/flat geometries in which dust grains grow and settle towards the midplane, and the bulk of the gas dissipates after 5 Myr, the picture of a disc around a more massive star is less clear. Therefore, we propose to observe a sample of 40 Herbig Be stars, in an effort to determine their disc properties. In particular, we aim at answering the following questions: 1) How do these discs dissipate?, 2) Does grain growth and settling occur? 3) Can gas giant planets still form, and what is the stellar upper mass limit for their formation?, and finally 4) How do the Herbig Be discs differ the lower mass Herbig Ae and T Tauri discs? To answer these questions, we propose to use PACS and SPIRE in photometric mode for the whole sample, and in spectroscopic mode for a subset of the 6 brightest - most promising targets. We will complement the proposed observations with existing optical to mid-IR photometry, as well as mid-IR spectroscopy, to construct spectral energy distributions (SED). These SEDs trace the dust continuum and will be analysed with the aid of radiative transfer modelling. For part of the sample, we also have mid-IR images or interferometry, revealing the spatial extend at those wavelengths. In a next step we will relate the derived disc properties with stellar properties. In addition, for the 6 spectroscopic targets we will be able to make a detailed case study of their cold dust and gas content: the forsterite feature at 69 micron reveals the iron content in the crystalline dust, and gas lines of e.g. OI and CO will allow us to constrain the amount of gas still present in the disc, using both radiative transfer modelling as well as thermo-chemical models. The proposed observations will provide a valuable database for a better understanding of the disc structure and evolution in the more massive Herbig Be type stars. |
