Gomez's Hamburger (IRAS 18059-3211): a pre main-sequence A-type star^*

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 Submillimeter Array, Harvard-Smithsonian Center for Astrophysics, 645 North A'ohoku Place, Hilo, HI 96720, USA e-mail: dfong@sma.hawaii.edu

Received: 19 December 2007
Accepted: 13 March 2008

Abstract

Aims. We study the nature of Gomez's Hamburger (IRAS 18059-3211; GoHam), a nebula that has been proposed to be a post-AGB object. Such a classification has not been confirmed; instead, we argue that it will be a key object in the study of disks rotating around young stars.

Methods. We present high-resolution SMA maps of CO J = 2-1 in Gomez's Hamburger. The data are analyzed by means of a code that simulates the emission of a nebula showing a variety of physical conditions and kinematics.

Results. Our observations clearly show that the CO emitting gas in Gomez's Hamburger forms a spectacular disk in keplerian rotation. Model calculations undoubtly confirm this result. The central (mainly stellar) mass is found to be high, ~4  for a distance of 500 pc. The mass and (relatively low) luminosity of the source are, independent of the assumed distance, very different from those possible in evolved stars. This object is probably transitional between the pre-MS and MS phases, still showing interstellar material around the central star or stellar system.