| Description |
The IRAS source 19312+1950 is a peculiar bipolar nebula that has eluded firm characterisation since its discovery. It exhibits maser and outflow properties similar to a massive O-rich AGB star, but shows molecular species such as CH3OH and HC3N that are more typically found in molecular clouds or YSOs. The source is surrounded by remarkable NIR nebulosity and has an unusual SED. The puzzle over the true nature of this object is confounded by our Spitzer IR spectrum that shows amorphous silicates and CO2 ice, but also emission from what may be crystalline silicates. In order to understand the physical properties of the gas and dust in the vicinity of IRAS 19312+1950, we propose to perform Herschel observations of emission from CO and H2O across a broad wavelength range from sub-mm to IR. Observations of transitions from a variety of energy levels will allow us to probe different temperature and density regimes within the source, from which we will construct a picture of its physical structure through radiative transfer/excitation modelling. HIFI observations will allow us to separate the broad and narrow molecular line components and PACS IFU mapping will provide crucial spatial information on the physical structure of the source. We also propose to perform a PACS SED scan to better characterise the source SED, and measure diagnostic spectral features of the dust and gas such as the forsterite 69 micron band, the OI 63 micron line and the N II 122 and 205 micron lines. The combination of these unique observations will help solve the puzzle of the nature of this peculiar object. |
