High-resolution study of a star-forming cluster in the Cepheus A HW2 region^*

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: ccomito@mpifr-bonn.mpg.de
² Instituto de Estructura de la Materia, Consejo Superior de Investigaciones Científicas, Departamento de Astrofísica Molecular e Infrarroja, C/Serrano 121, 28006 Madrid, Spain

Received: 5 March 2007
Accepted: 28 March 2007

Abstract

Context.Due to its relatively small distance (725 pc), the Cepheus A East star-forming region is an ideal laboratory to study massive star formation processes.

Aims.Based on its morphology, it has been suggested that the flattened molecular gas distribution around the YSO HW2 may be a 350-AU-radius massive protostellar disk. The goal of our work is to ascertain the nature of this structure.

Methods.We have employed the Plateau de Bure Interferometer to acquire (sub-)arcsecond-resolution imaging of high-density and shock tracers, such as methyl cyanide (CH₃CN) and silicon monoxide (SiO), towards the HW2 position.

Results.On the (~ AU) scale, the flattened distribution of molecular gas around HW2 appears to be due to the projected superposition, on the plane of the sky, of at least three protostellar objects, of which at least one is powering a molecular outflow at a small angle with respect to the line of sight. The presence of a protostellar disk around HW2 is not ruled out, but such structure is likely to be detected on a smaller spatial scale, or using different molecular tracers.