Imaging the disk around IRAS 20126+4104 at subarcsecond resolution^⋆

¹ INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
e-mail: cesa@arcetri.astro.it; galli@arcetri.astro.it; walmsley@arcetri.astro.it
² Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 Saint Martin d’Hères, France
e-mail: neri@iram.fr
³ Dublin Institute for Advanced Studies (DIAS), 31 Fitzwilliam Place, 2 Dublin, Ireland

Received: 15 November 2013
Accepted: 9 May 2014

Abstract

Context. The existence of disks around high-mass stars has yet to be established on a solid ground, as only few reliable candidates are known to date. The disk rotating about the ~10⁴ L_⊙ protostar IRAS 20126+4104 is probably the most convincing of these.

Aims. We would like to resolve the disk structure in IRAS 20126+4104 and, if possible, investigate the relationship between the disk and the associated jet emitted along the rotation axis.

Methods. We performed observations at 1.4 mm with the IRAM Plateau de Bure interferometer attaining an angular resolution of ~0.̋4 (~660 AU). We imaged the methyl cyanide J = 12 → 11 ground state and vibrationally excited transitions as well as the CH₃¹³CN isotopologue, which had proved to be disk tracers.

Results. Our findings confirm the existence of a disk rotating about a ~7–10 M_⊙ star in IRAS 20126+4104, with rotation velocity increasing at small radii. The dramatic improvement in sensitivity and spectral and angular resolution with respect to previous observations allows us to establish that higher excitation transitions are emitted closer to the protostar than the ground state lines, which demonstrates that the gas temperature is increasing towards the centre. We also find that the material is asymmetrically distributed in the disk and speculate on the possible origin of such a distribution. Finally, we demonstrate that the jet emitted along the disk axis is co-rotating with the disk.

Conclusions. We present iron-clad evidence of the existence of a disk undergoing rotation around a B-type protostar, with rotation velocity increasing towards the centre. We also demonstrate that the disk is not axially symmetric. These results prove that B-type stars may form through disk-mediated accretion as their low-mass siblings do, but also show that the disk structure may be significantly perturbed by tidal interactions with (unseen) companions, even in a relatively poor cluster such as that associated with IRAS 20126+4104.