The physical conditions in gomez's hamburger (IRAS18059-3211), a pre-MS rotating disk

Abstract

Aims. We aim to study the structure, dynamics, and physical conditions of Gomez's Hamburger (IRAS18059-3211; GoHam), and in particular confirm that GoHam mainly consists of a flaring disk in Keplerian rotation around a young, probably pre-MS star.Methods. We present high resolution SMA maps of 12CO J = 2-1, 13CO J = 2-1, 12 CO J = 3-2, and C17O J = 3-2, as well as data on 12CO J = 6-5 and the continuum flux at these wavelengths. Spatial resolutions as high as 1 are attained. Except for the C17O data, the dynamical ranges are larger than 10. The maps are compared with a numerical model, which simulates the emission of a rotating disk with the expected general properties of such objects, and a very satisfactory fitting of our maps is obtained. The meaning and reliability of our results are thoroughly discussed. Results. Our observations allow measurement of the main properties of GoHam on scales of between ∼1 (∼5 X 1015 cm, for the assumed distance, 300 pc) and the total extent of the nebula, 14. We are able to measure the global structure of the gas-rich disk, which is found to be flaring, and its dynamics, which is clearly dominated by Keplerian rotation, with a small degree of turbulence. The combination of different lines, in particular of different opacities, allows us to estimate reasonably the distributions of gas temperature and density. We clearly find a significant and sharp increase in temperature at large distances from the equator, accompanied by a decrease in density of the same order. Finally, we identify a condensation in the southern part of the disk that has no counterparts in the northern nebula. This condensation is quite extended (about 5 X 1015 cm), contains a significant amount of mass (roughly,∼6 X 10-3 M ȯ), and seems to be associated with a detectable distortion of the global rotation kinematics. We discuss several possible interpretations of that feature. © 2009 ESO.