A study of the Keplerian accretion disk and precessing outflow in the massive protostar IRAS 20126+4104

¹ Osservatorio Astrofisico di Arcetri, INAF, Largo E. Fermi 5, 50125 Firenze, Italy e-mail: cesa@arcetri.astro.it
² IRAM, 300 rue de la Piscine, Domaine Universitaire, 38406 St. Martin d'Hères Cedex, France
³ Istituto di Radioastronomia, CNR, Sezione di Firenze, Largo E. Fermi 5, 50125 Firenze, Italy
⁴ Physics Department, New Mexico Tech, 801 Leroy Place, Socorro, NM 87801, USA
⁵ National Radio Astronomy Observatory, PO Box O, Socorro, NM 87801, USA

Received: 12 July 2004
Accepted: 16 January 2005

Abstract

We report on interferometric observations at 3.2 and 1.3 mm of the massive young stellar object IRAS 20126+4104 obtained in the C³⁴S and CH₃OH lines and in the continuum emission. The C³⁴S data confirm the existence of a Keplerian disk, as already suggested by various authors. However, the mass of the central object is ~7 , significantly less than previous estimates. We believe that such a discrepancy is due to the fact that the rotation curve is affected not only by the star but also by the mass in the innermost regions of the disk itself: this leads to an overestimate of the stellar mass when low-density tracers are used to study the velocity field over regions larger than a few seconds of arc (i.e. a few 0.01 pc). On the basis of the line profiles we speculate that accretion onto the star might be still occurring through the disk. This seems consistent with current models of high-mass star formation which predict an accretion luminosity equal to that of IRAS 20126+4104 for a 7  protostar. The CH₃OH lines trace both the disk and the bipolar outflow previously detected in other molecules such as HCO⁺, SiO, and H₂. New H₂ images obtained at 2.2 μm confirm that the outflow axis is undergoing precession. We elaborate a simple model that suitably fits the data thus allowing derivation of a few basic parameters of the precession.