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

¹ Observatorio Astronómico Nacional (OAN-IGN), Apartado 112, 28803 Alcalá de Henares, Spain e-mail: v.bujarrabal@oan.es
² Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA e-mail: rtm@cfa.harvard.edu
³ Institut de RadioAstronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 St. Martin d'Hères, France e-mail: ccarrizo@iram.fr

Received: 27 October 2008
Accepted: 2 February 2009

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  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″ (~510¹⁵ 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 510¹⁵ cm), contains a significant amount of mass (roughly, ~610^-3 ), and seems to be associated with a detectable distortion of the global rotation kinematics. We discuss several possible interpretations of that feature.