Letter to the Editor

Forming an early O-type star through gas accretion?

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: lzapata@mpifr-bonn.mpg.de
² Laboratorio de Astrofísica Espacial y Física Fundamental, Apartado 78 28691 Villanueva de la Cañada, Madrid, Spain
³ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
⁴ Academia Sinica Institute of Astronomy and Astrophysics, Taipei, Taiwan
⁵ CRyA, Universidad Nacional Autónoma de México, Apdo. Postal 3-72 (Xangari), 58089 Morelia, Michoacán, México

Received: 12 October 2007
Accepted: 29 November 2007

Abstract

We present high angular resolution (~3'') and sensitive 1.3 mm continuum, cyanogen (CN) and vinyl cyanide (C₂H₃CN) line observations made with the Submillimeter Array (SMA) toward one of most highly obscured objects of the W51 IRS2 region, W51 North. We find that the CN line exhibits a pronounced inverse P-Cygni profile indicating that the molecular gas is falling into this object with a mass accretion rate between 4 and 7  10 yr^-1. The C₂H₃CN traces an east-west rotating molecular envelope that surrounds either a single obscured (proto)star with a kinematic mass of 40  or a small central cluster of B-type stars and that is associated with a compact high velocity bipolar outflow traced by H₂O masers and SiO molecular emission. We thus confirm that the W51 North region is part of the growing list of young massive star forming regions that have been associated with infalling motion and with high mass accretion rates (~10^-2-10 yr^-1), strengthening the evidence that massive stars can form with very high accretion rates sufficient to quench the formation of a UCHII region.