The physical conditions in Gomez's Hamburger (IRAS 18059-3211), a pre-MS rotating disk

Abstract

Aims: We aim to study the structure, dynamics, and physical conditions of Gomez's Hamburger (IRAS 18059-3211; 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, ¹²CO 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 arcsec ( 5×10¹⁵ cm, for the assumed distance, 300 pc) and the total extent of the nebula, 14 arcsec. 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 5×10¹⁵ cm), contains a significant amount of mass (roughly, 6×10^-3 M_{⊙}), and seems to be associated with a detectable distortion of the global rotation kinematics. We discuss several possible interpretations of that feature.

Appendix A is only available in electronic form at http://www.aanda.org